neuropeptide-y and atrinositol

The aim of this study was to examine the effects of D-myo-inositol-1,2,6-trisphosphate (alpha-trinositol) on haemodynamic variables and neuropeptide Y (NPY) levels in hypertensives and healthy volunteers.. Hypertensives (n = 13) and normotensives (n = 11) were recruited after a screening of cardiovascular risk factors of all men aged 40 living in a well defined area. The hypertensives were previously unmedicated. The effect of alpha-trinositol was studied after intravenous infusion at rest, and during and after a maximal exercise test in a double-blind crossover manner with placebo.. Haemodynamic variables and NPY levels were recorded. NPY levels did not differ between normotensives and mild hypertensives at the start of the study. However, a significant increase was seen in hypertensives after they had risen to the sitting position. During exercise, the NPY levels increased significantly both in normotensives and hypertensives. After the exercise test, the NPY levels were significantly higher in hypertensives than in normotensives; alpha-trinositol did not modify these responses. In normotensives no significant difference in systolic blood pressure was seen during or after the exercise test whether they were on alpha-trinositol or placebo. In the hypertensives on active drug, however, the blood pressure tended to be approximately 5 mmHg lower during the exercise test as compared with the placebo group. In the hypertensives on active drug, the heart rate increased significantly more during exercise as compared with the placebo groups. In normotensives, the same tendency was seen, but it did not reach statistical significance.. The NPY antagonist, alpha-trinositol, tends to reduce the increase in systolic blood pressure induced by maximal exercise and increases the heart rate in hypertensives but not in normotensives.

Topics: Adult; Blood Pressure; Cross-Over Studies; Double-Blind Method; Heart Rate; Hemodynamics; Humans; Hypertension; Inositol Phosphates; Male; Neuropeptide Y; Pilot Projects

Hyperphagia followed both central neuropeptide Y (NPY) administration and the presumed increase of endogenous NPY activity after food deprivation. NPY induced greater hyperphagia in cold-adapted than non-adapted rats; fasting of comparable severity caused similar hyperphagia in the two groups. NPY-receptor-antagonist D-Tyr(27,36), D-Thr32-NPY(27,36) or functional NPY-antagonist D-myo-inositol-1,2,6-trisphosphate attenuated the hyperphagic effect of both NPY and fasting in non-adapted rats. However, while completely preventing the NPY-hyperphagia, they did not influence the fasting-induced hyperphagia in cold-adapted rats. With cold-adaptation the sensitivity to NPY and to its antagonists increases, but the hypothalamic NPY loses from its fundamental role in the regulation of food intake, and the hyperphagia seen in cold-adaptation may need some other explanation.

Topics: Animals; Body Weight; Cold Temperature; Feeding Behavior; Female; Food Deprivation; Hyperphagia; Injections, Intraventricular; Inositol Phosphates; Neuropeptide Y; Peptide Fragments; Rats; Rats, Wistar

To evaluate whether alpha-trinositol may have an effect on the microcirculation in patients with diabetes mellitus and critical ischaemia.. Ten patients with previously known diabetes mellitus and with critical limb ischaemia were given alpha-trinositol during a 24 h infusion, resulting in a total dose of 2400 mg. Microcirculation was evaluated by means of laser doppler fluxmetry (LDF), transcutaneous oxygen tension (tcPO2) and dynamic capillaroscopy (CBV).. Plasma concentration of alpha-trinositol reached a steady state level after 1 h following the start of the administration. There were no detectable changes in blood pressure or heart rate. Laser Doppler flux increased from 41% to 57.5% and tcPO2 changed from 116 to 91 s in "half time recovery" after occlusion. Capillary blood flow showed an increase in resting velocity from 0.1 to 0.5 mm/s at 24 h.. The infusion of alpha-trinositol did not cause any changes in the haemodynamics in general, but resulted in changes in LDF(rest value), tcO2(half-time recovery) and CBV(rest flow) during or following the infusion suggesting improved microcirculation.

Topics: Aged; Aged, 80 and over; Analysis of Variance; Blood Circulation; Blood Flow Velocity; Blood Gas Monitoring, Transcutaneous; Capillaries; Confidence Intervals; Diabetes Complications; Electroencephalography; Extremities; Female; Hemodynamics; Humans; Inositol Phosphates; Ischemia; Laser-Doppler Flowmetry; Male; Microcirculation; Microscopy, Video; Middle Aged; Neuropeptide Y; Pilot Projects; Platelet Aggregation Inhibitors; Statistics, Nonparametric

Systemic infusion of neuropeptide Y (NPY; 1 microg kg-1 min-1) for 120 min rapidly reduced renal blood flow and increased mean arterial pressure and renovascular resistance and, at later time points (> 30 min), enhanced diuresis, natriuresis and calciuresis in anaesthetized rats. Infusion of the reported NPY antagonist PP56 (D-myo-inositol 1,2,6-triphosphate, 333 mg kg-1 min-1) slightly but significantly enhanced renal blood flow and reduced renovascular resistance over the course of the infusion period. Infusion of PP56 together with NPY (starting 30 min prior to the NPY infusion) significantly inhibited NPY-induced alterations of mean arterial pressure, renal blood flow and renovascular resistance. Coinfusion of PP56 also attenuated the renovascular effects of bolus injections of NPY (0.1-10 microg/kg) but at the highest NPY dose the antagonistic effect of PP56 could partially be overcome. In contrast to the antagonism of the vascular NPY effects, infusion of PP56 did not significantly affect NPY-induced enhancements of diuresis, natriuresis and calciuresis. Thus, PP56 is a surmountable antagonist of vascular but not tubular NPY effects. We conclude that tubular NPY effects occur largely independently of alterations of renal haemodynamics.

Topics: Anesthesia; Animals; Dose-Response Relationship, Drug; Inositol Phosphates; Male; Neuropeptide Y; Platelet Aggregation Inhibitors; Rats; Rats, Wistar; Renal Circulation; Vascular Resistance

In normal animals, spinal administration of neuropeptide Y induces analgesia to thermal stimuli, but has no effect on mechanical thresholds. Recent anatomical studies, however, have shown that following nerve injury there is an altered expression of neuropeptide Y and its receptors. The aim of this behavioural study, therefore, is to examine the effect of intrathecal administration of neuropeptide Y, its agonists and an antagonist on mechanical nociceptive thresholds in rats with partial injury to the sciatic nerve. Test agents were administered for 14 days via osmotic pumps (0.5 microliter/day) attached to intrathecal catheters and the nociceptive flexion reflex was quantified using an Ugo Basile Analgesymeter. Partial injury to the sciatic nerve, in animals treated intrathecally with saline, induces a significant decrease in mechanical threshold as compared to the sham operated, contralateral paw. The nerve injury-induced hyperalgesia is exacerbated by 2 microM neuropeptide Y and by 2 microM [Leu31,Pro34]-neuropeptide Y, a Y1 receptor agonist. The Y2 receptor agonist, N-acetyl-[Leu28,Leu31]-neuropeptide Y24-36 (2 microM), had no effect on the nerve injury-induced hyperalgesia. The putative neuropeptide Y antagonist, alpha-trinositol (10 microM), significantly attenuated the nerve injury-induced hyperalgesia. This study suggests that neuropeptide Y may contribute to nerve injury-induced mechanical hyperalgesia via the Y1 receptor and provides further insight into the possible mechanisms underlying nerve injury-induced hyperalgesia to mechanical stimuli.

Topics: Analysis of Variance; Animals; Anti-Inflammatory Agents, Non-Steroidal; Functional Laterality; Hyperalgesia; Injections, Spinal; Inositol Phosphates; Neuropeptide Y; Pain; Rats; Rats, Wistar; Receptors, Neuropeptide Y; Sciatic Nerve; Sensory Thresholds; Spinal Cord

The effect of neuropeptide Y inhibition with alpha-trinositol on the cerebral blood flow autoregulation was studied in Wistar Kyoto rats. alpha-Trinositol was tested in two doses: one dose (5 mg kg-1 hr-1) selectively affecting neuropeptide Y and one higher dose (50 mg kg-1 hr-1) affecting both neuropeptide Y and the adrenergic response. The cerebral blood flow was measured with the intracarotid 133xenon injection method in halothane nitrous oxide-anaesthetized animals. Blood pressure was raised by norepinephrine infusion and lowered by controlled haemorrhage in separate groups of rats. In addition we examined the effect of alpha-trinositol on neuropeptide Y-induced contraction of cerebral vessels in vitro. The in vitro study demonstrated inhibition of neuropeptide Y-induced contraction with a alpha-trinositol dose selective of neuropeptide Y. The in vivo study demonstrated that cerebral blood flow autoregulation was preserved after both doses of alpha-trinositol. alpha-Trinositol in the low neuropeptide Y-selective dose (5 mg kg-1 hr-1) did not affect the blood pressure limits of cerebral blood flow autoregulation, but the higher dose (50 mg kg-1 hr-1) of alpha-trinositol shifted the upper blood pressure limit of cerebral blood flow autoregulation towards lower blood pressures, an effect probably due to inhibition of both the adrenergic and neuropeptide Y systems.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Blood Pressure; Cerebral Arteries; Cerebrovascular Circulation; Dose-Response Relationship, Drug; Homeostasis; In Vitro Techniques; Inositol Phosphates; Male; Muscle Contraction; Muscle, Smooth, Vascular; Neuropeptide Y; Rats; Rats, Inbred WKY

Cutaneous microcirculatory changes were measured by laser-Doppler flowmetry in response to electrical stimulation of sympathetic efferent fibres of the rat's saphenous nerve. After perineural capsaicin (2%) pretreatment, electrical stimulation of the peripheral stump of the cut saphenous nerve evoked a reduction in blood flow (vasoconstriction) followed by a minimal enhancement. This late vasodilatation was further reduced by resiniferatoxin (1 microg/kg i.v.), and vasoconstriction was abolished by guanethidine (8 mg/kg i.v.), indicating the involvement of sensory and sympathetic fibres in the respective responses. The vasoconstrictor response was analysed after blockade of antidromic vasodilatation by combined capsaicin-resiniferatoxin pretreatment. alpha-Adrenoceptor antagonists (1 mg/kg phentolamine, 0.5 mg/kg prazosin and 1 mg/kg GYKI-12743 (RS-2-(3)N-(2-benzo;1,4i-dioxanyl)-methylamino(propyl)-3(2H) -piridazinone hydrochloride) inhibited, but did not eliminate the blood flow reduction evoked by 3 Hz stimulation. At 10 Hz stimulation significant inhibition was obtained only with GYKI-12743. No inhibition was observed with propranolol (10 microg/kg) on any occasion. A functional neuropeptide Y antagonist, alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56; 50 mg/kg i.v.), markedly diminished the vasocontrictor response remaining after treatments with the alpha-adrenoceptor blocking agents. Inhibition was more pronounced at 10 Hz. Since 3 Hz corresponds to an average, and 10 Hz approaches the maximal firing rate of the sympathetic efferents, these results emphasise the significant role of neuropeptide Y in regulation of the cutaneous microcirculation by sympathetic fibres under physiological circumstances, particularly during high activity.

Topics: Adrenergic alpha-Antagonists; Animals; Dioxanes; Electric Stimulation; Female; Inositol Phosphates; Laser-Doppler Flowmetry; Nerve Fibers; Neurons, Efferent; Neuropeptide Y; Norepinephrine; Platelet Aggregation Inhibitors; Pyridazines; Rats; Rats, Wistar; Regional Blood Flow; Skin; Sympathetic Nervous System

1. D-Myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes antagonism of a number of neuropeptide Y (NPY)-mediated cellular processes. The ability of pp56 to inhibit selectively the myocardial contraction mediated by NPY in relation to the responses to other cardioactive peptides, including endothelin-1, calcitonin gene-related peptide (CGRP), secretin and vasoactive intestinal peptide (VIP), was assessed. In order to investigate the possible interaction of pp56 with mechanisms of inositol phosphate signalling generated in heart muscle cells by activation of the beta-isoenzyme of phospholipase C (PLC beta), noradrenaline was used as a positive control, and isoprenaline and forskolin were included as negative controls. 2. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM). The concentrations of agonists used were in the region of their maximally effective concentrations for myocyte contraction and the concentration of pp56 was in the range of 1-100 microM. Contractile activity was monitored by video microscopy and maximum shortening determined by image analysis. 3. In the absence of agonist, contractile amplitudes following 20 min preincubation with pp56 were not different from that observed in the absence of pp56. Pp56 (1-100 microM) inhibited significantly the positive contractile response to noradrenaline (5 microM) in the presence of propranolol (500 nM), such that the response was almost completely attenuated at the highest concentration of the inhibitor. Pp56 did not inhibit the positive contractile responses to forskolin (40 microM) or isoprenaline (100 nM). 4. NPY alone does not influence the basal level of contraction of cardiomyocytes, but can attenuate isoprenaline-stimulated contraction and can increase contractile amplitude from basal when the transient outward current is blocked with 4-aminopyridine. In the presence of isoprenaline (100 nM), the negative response to NPY (100 nM) was attenuated significantly by pp56 (1-100 microM). With 4-aminopyridine, the positive contractile response to NPY (200 nM) was decreased by pp56, although this was not statistically significant. 5. Pp56 inhibited the positive contractile responses to CGRP (1 nM) and endothelin-1 (20 nM) completely, but did not affect the responses to secret

Topics: Animals; Appetite Stimulants; Cardiotonic Agents; Dose-Response Relationship, Drug; Heart; Heart Ventricles; Inositol Phosphates; Male; Myocardial Contraction; Myocardium; Neuropeptide Y; Peptides; Platelet Aggregation Inhibitors; Rats; Rats, Sprague-Dawley; Stimulation, Chemical; Type C Phospholipases

Neuropeptide Y is a sympathetic co-neurotransmitter released with noradrenaline upon sympathetic nerve stimulation. This study describes the ability of a synthetic inositol phosphate, alpha-trinositol(D-myo-inositol 1,2,6-triphosphate; PP 56) to antagonize vasoconstrictor responses to neuropeptide Y in-vitro as well as in-vivo. In human and guinea-pig isolated arteries alpha-trinositol potently (10 nM to 1 microM extracellular concentration) suppressed the constriction evoked by neuropeptide Y alone, the potentiation by neuropeptide Y of noradrenaline-evoked constriction, and the neuropeptide Y-induced inhibition of relaxation. Moreover, in the pithed (areflexive) rat, a non-adrenergic portion of the pressor response to preganglionic sympathetic nerve stimulation was sensitive to alpha-trinositol. As studied in the recently cloned human (vascular-type) Y1 receptor, the action of alpha-trinositol does not occur through antagonism at the neuropeptide Y recognition site nor does it induce allosteric changes of this receptor. However, we found alpha-trinositol to inhibit the rise in intracellular Ca2+ as well as inositol triphosphate concentrations induced by neuropeptide Y. It is, therefore, proposed that alpha-trinositol represents a non-receptor, but yet selective antagonist of neuropeptide Y in vasculature, opening up the possibility to investigate involvement of neuropeptide Y in sympathetic blood pressure control and in cardiovascular disorders.

Topics: Adrenergic alpha-Antagonists; Animals; Arteries; Basilar Artery; Calcium; Dose-Response Relationship, Drug; Endothelium, Vascular; Female; Guinea Pigs; Humans; In Vitro Techniques; Inositol Phosphates; Male; Muscle Contraction; Muscle, Smooth, Vascular; Neuropeptide Y; Norepinephrine; Platelet Aggregation Inhibitors; Prazosin; Rats; Rats, Sprague-Dawley; Skin; Synaptic Transmission; Uterus; Vas Deferens; Vasoconstriction

Electrical stimulation of the peripheral stump of the cut and perineurally capsaicin-pretreated saphenous nerve evokes antidromic vasodilatation preceded by a short vasoconstriction in the dorsal skin of the hindpaw in the rat. These microcirculatory changes were measured by laser-Doppler flowmetry. Blood flow increase induced by nerve stimulation was completely abolished by 1 microgram/kg resiniferatoxin (RTX), while the inicial blood flow decrease was significantly reduced or totally inhibited by subsequent treatments with an alpha adrenergic receptor antagonist (GYKI-12743) and a neuropeptide Y functional antagonist (alpha-trinositol) in response to 10 Hz and 3 HZ stimulations, respectively.

Topics: Adrenergic Antagonists; Animals; Blood Circulation; Capsaicin; Electric Stimulation; Foot; Inositol Phosphates; Microcirculation; Nervous System Physiological Phenomena; Neuropeptide Y; Rats; Rats, Wistar; Regional Blood Flow; Skin; Sympathetic Nervous System; Vasodilation

Previous studies have demonstrated that alpha-trinositol (D-myo-inositol-1.2.6-trisphosphate; PP56) may act as a functional neuropeptide Y (NPY) inhibitor. Because NPY is known to be a potent vasoconstrictor, the effects of alpha-trinositol on renal function, vascular responses and the potentiating effects of NPY were investigated in rats with congestive heart failure (CHF) induced by ligation of the left coronary artery. Incremental doses of alpha-trinositol were given to conscious rats (bolus 2, 4 or 10 mg/kg i.v. followed by a 15-minute infusion 20, 40 and 100 mg/kg/h, respectively). Urinary volume, sodium and potassium excretions were significantly increased in both CHF and sham-operated control animals after alpha-trinositol administration compared with saline. Diuresis and natriuresis were observed also during co-administration of alpha-trinositol with NPY but not with norepinephrine (NE). In the pithed CHF rats, threshold doses of NPY potentiated the pressor effects of endothelin-1 (ET-1) and angiotensin II (AII), but not preganglionic nerve stimulation or phenylephrine administration. Alpha-trinositol antagonized both the pressor response to NPY and the potentiation by NPY of pressor responses to effects of ET-1 and AII. Our data show that alpha-trinositol exhibis diuretic and natriuretic effects as well as vascular antagonistic effects on NPY in normal and CHF rats. These effects of alpha-trinositol may be due to an interaction with NPY mediated antidiuresis and antinatriuresis.

Topics: Animals; Cardiovascular System; Diuresis; Heart Failure; Hemodynamics; Inositol Phosphates; Kidney; Male; Myocardial Ischemia; Natriuresis; Neuropeptide Y; Rats; Rats, Sprague-Dawley

Injury of peripheral nerves often results in hyperalgesia (an increased sensitivity to painful stimuli). This hyperalgesia is mediated in part by sympathetic neurotransmitters. We examined the effect of neuropeptide Y (NPY), specific Y1 and Y2 agonists, and an NPY antagonist on peripheral hyperalgesia in rats whose sciatic nerves had been partially transected. NPY and the Y2 agonist, N-acetyl [Leu28,Leu31] NPY 24-36 exacerbated both mechanical and thermal hyperalgesia, while the Y1 agonist, [Leu31, Pro34]NPY relieved thermal hyperalgesia. Mechanical and thermal hyperalgesia were both relieved by alpha-trinositol (PP56), a non-competitive antagonist of the actions of neuropeptide Y. Hyperalgesia was also relieved by surgical sympathectomy, which eliminated the effects of NPY and its agonists. These results suggest that neuropeptide Y contributes to peripheral hyperalgesia by actions at Y2 receptors, which may be located on postganglionic sympathetic terminals.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Disease Models, Animal; Female; Hyperalgesia; Inositol Phosphates; Neuropeptide Y; Rats; Rats, Wistar; Sciatic Nerve; Sympathectomy

We have studied the effects of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56), a putative antagonist of neuropeptide Y receptors, on the nociceptive flexor reflex in decerebrate, spinalized rats after intrathecal and intravenous administration. Intrathecal alpha-trinositol caused strong and prolonged facilitation of the flexor reflex, which was usually associated with an increase in spontaneous motoneuron activity. The reflex depressive effect of intrathecal neuropeptide Y was neither blocked nor reversed by alpha-trinositol. Intravenous alpha-trinositol at low doses had no effect on the flexor reflex and at high dose, reflex facilitation was sometimes observed. It is concluded that alpha-trinositol acts as a spinal excitant and is not an antagonist of the neuropeptide Y receptor in the rat spinal cord.

Topics: Animals; Dose-Response Relationship, Drug; Female; Injections, Spinal; Inositol Phosphates; Neuropeptide Y; Rats; Rats, Sprague-Dawley; Reflex; Spinal Cord

alpha-Trinositol (1D-myo-inositol 1,2,6-trisphosphate, PP56) selectively and potently inhibits the vasoconstrictor effects of neuropeptide Y (NPY). The authors used quantitative in vitro receptor autoradiography to localize and characterize [3H]alpha-trinositol binding sites in human and mammalian tissues. [3H]alpha-trinositol bound specifically to vascular and nonvascular smooth muscle in human, porcine and rat tissues. Binding was time dependent, reversible, saturable and specific for alpha-trinositol compared with inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) and inositol hexakisphosphate (Ins-P6). Binding to each structure gave Kd values of 5 to 20 nM and was consistent with a homogeneous population of sites. Binding was optimal at pH 5 and at low calcium concentrations. Comparison with [125I]Bolton Hunter-labeled NPY ([125I]BH-NPY) binding in porcine tissues revealed 1) a partial colocalization but Bmax values for [3H]alpha-trinositol binding some two orders of magnitude higher than for [125I]BH-NPY and 2) failure of each of the two ligands to inhibit binding of the other. Comparison of [3H]alpha-trinositol with [3H]Ins-1,3,4,5-P4 binding in human umbilical cord revealed that both ligands bound specifically to vascular smooth muscle but that only [3H]Ins-1,3,4,5-P4 bound to arterial endothelium. Both ligands bound to sites with rank orders of affinity Ins-1,3,4,5-P4 > Ins-P6 > inositol 1,4,5-trisphosphate. alpha-Trinositol had, however, three orders of magnitude higher affinity for [3H]alpha-trinositol than [3H]Ins-1,3,4,5-P4 binding sites; Ins-1,3,4,5-P4 and Ins-P6 had higher affinity for [3H]Ins-1,3,4,5-P4 binding sites. Specific [3H]alpha-trinositol binding sites may represent receptors by which alpha-trinositol inhibits NPY effects on vascular tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Aged; Animals; Anti-Inflammatory Agents, Non-Steroidal; Autoradiography; Binding Sites; Colon; Female; Humans; Inositol Phosphates; Male; Middle Aged; Muscle, Smooth, Vascular; Neuropeptide Y; Rats; Rats, Wistar; Spleen; Swine; Synovial Membrane; Umbilical Cord

It is considered that cyclic guanosine monophosphate (cGMP) plays a pivotal role in mediating the relaxation of vascular and nonvascular smooth muscles. cGMP steady state levels are regulated by guanylyl cyclase, cGMP phosphodiesterases and its flux from cells. The present study examines the possible relation between cerebrovascular vasodilator agents and generation of cGMP in guinea pig cerebral vessels. Acetylcholine, substance P, nitroglycerine and sodium nitroprusside significantly increased the generation of cGMP. The application of acetylcholine, substance P, nitroglycerine and sodium nitroprusside elicited concentration-dependent relaxation of basilar artery segments. Neuropeptide Y increased the generation of cGMP by 2%-46% of control levels (at 10(-7)-10(-6)M of neuropeptide Y; *P < 0.05). In addition, neuropeptide Y (10(-6)M) induced a transient relaxation of the precontracted guinea pig basilar arteries with endothelium. This transient relaxation was blocked by nitro-L-arginine (10(-4)M). alpha-Trinositol does not alter the formation of cGMP nor the neuropeptide Y-induced relaxation. In the presence of alpha-trinositol neuropeptide Y (10(-7)-10(-6)M) did not significantly elevate the production of cGMP as compared with controls. The rise in cGMP induced by acetylcholine, substance P and nitroglycerine was slightly increased by the addition of neuropeptide Y (3 x 10(-7) M). Acetylcholine and substance P induced an endothelium-dependent relaxation of the precontracted guinea pig basilar arteries, while sodium nitroprusside and nitroglycerine induced an endothelium-independent relaxation. Acetylcholine, substance P and nitroglycerine induced concentration-dependent relaxations of basilar artery, respectively. The relaxation elicited by acetylcholine or substance P, but not nitroglycerine, was markedly attenuated by neuropeptide Y (3 x 10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetylcholine; Animals; Basilar Artery; Brain; Cerebral Arteries; Cerebral Veins; Cyclic GMP; Drug Interactions; Guinea Pigs; In Vitro Techniques; Inositol Phosphates; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Neuropeptide Y; Nitroglycerin; Nitroprusside; Platelet Aggregation Inhibitors; Radioimmunoassay; Substance P; Vasodilator Agents

The antinociceptive effect of alpha-trinositol was examined in rats using the formalin test following systemic, spinal and local subcutaneous administration. Injection of formalin into the paw evoked two phases (phase 1: 0-9 min; phase 2: 10-60 min) of flinching behavior of the injected paw. Intrathecal administration of alpha-trinositol resulted in a dose-dependent suppression of the first (ED50: 8 microg) and second (ED50: 9 microg) phase of formalin-evoked behavioral response. Similarly, intraperitoneal delivery showed a dose-dependent reduction of the first (ED50: 83 mg/kg) and second (ED50: 56 mg/kg) phase of the formalin test. Subcutaneous injection of 100 microg, but not 10 mu g, alpha-trinositol into the rat paw together with the formalin solution, had no effect on the first phase, but reduced by 20% the second phase of behavior. These data show that alpha-trinositol produces a suppression of acute and prolonged nociceptive behaviors with a central mechanism of action, although some peripheral component may contribute to the reduction of the late phase following systemic administration.

Topics: Analgesia; Animals; Anti-Inflammatory Agents, Non-Steroidal; Dose-Response Relationship, Drug; Formaldehyde; Inositol Phosphates; Male; Neuropeptide Y; Prostaglandins; Rats; Rats, Sprague-Dawley

The purpose of the present study was to investigate the presence and vascular effects of neuropeptide Y in the rabbit orbital arteries. Neuropeptide Y-containing nerve fibers were demonstrated, using an indirect immunofluorescence method with a neuropeptide Y antiserum raised in goat against porcine neuropeptide Y. Isometric responses in isolated circular segments of the orbital arteries were measured following application of neuropeptide Y, different contracting agonists, and the neuropeptide Y blocker alpha-trinositol. A rich supply of neuropeptide Y-containing nerve fibers was seen around the orbital arteries. Neuropeptide Y (10(-10)-10(-6) M) did not induce any contractions in resting arterial segments. Noradrenaline and histamine evoked concentration dependent constrictions which were potentiated by neuropeptide Y (3 x 10(-7) M). This potentiation was completely blocked by alpha-trinositol (3 x 10(7) M). The contractile effects of endothelin-1, endothelin-3, prostaglandin F2 alpha, and 5-hydroxytryptamine were not modified by neuropeptide Y.

Topics: Animals; Arteries; Chinchilla; Histamine; Immunohistochemistry; Inositol Phosphates; Neuropeptide Y; Norepinephrine; Orbit; Prazosin; Rabbits; Vasoconstriction; Vasomotor System

Neuropeptide Y is known to be present in significant amounts in the retina of most vertebrates, but its physiological actions are largely unknown. We have therefore studied its effects on the intracellular cyclic AMP accumulation in rabbit retina. Neuropeptide Y had no effect on the basal cyclic AMP level but was found to inhibit the forskolin induced cyclic AMP accumulation. There were no differences between the effects of neuropeptide Y 1-36 and neuropeptide Y 13-36 (2.4 x 10(-6) M) suggesting the presence of the Y2 subtype of neuropeptide Y receptor. D-myo-inositol-1,2,6-trisphosphate, a novel neuropeptide Y-antagonist, reduced per se the forskolin induced cyclic AMP production. The pronounced inhibitory effect of neuropeptide Y on the forskolin induced cyclic AMP production was, on the other hand, totally abolished by D-myo-inositol-1,2,6-trisphosphate. The results indicate that neuropeptide Y acts on Y2 receptors in the retina to cause an inhibition of the adenylyl cyclase activity which could be antagonized by D-myo-inositol-1,2,6-trisphosphate. Such an inhibitory action of neuropeptide Y is similar to what has been found in brain tissue, but it has not previously been reported in the retina for neuropeptide Y or any of the other retinal neuropeptides.

Topics: 1-Methyl-3-isobutylxanthine; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Animals; Colforsin; Cyclic AMP; Inositol Phosphates; Neuropeptide Y; Rabbits; Receptors, Neuropeptide Y; Retina

There is much data showing correlation between forskolin-induced relaxation and production of cyclic AMP. But are these processes coupled or two phenomena occurring in parallel? This question was studied in guinea-pig cerebral vessels by using NPY as a strong inhibitor and alpha-trinositol as its antagonist. The basal cyclic AMP content of cerebral vessel segments in the control group was 670 +/- 53 fmol/mg wet weight (w.w.). Forskolin (10(-7), 3 x 10(-7) and 10(-6) M) increased the formation of cyclic AMP to 738 +/- 86 (ns), 699 +/- 81 (ns) and 1158 +/- 132 fmol/mg w.w. (p < 0.05), respectively. alpha-trinositol (10(-8)-10(-6) M) neither reduced the formation of cyclic AMP compared to basal cyclic AMP levels nor affected the forskolin-stimulated increase of cyclic AMP (p > 0.05). On the other hand, NPY (10(-7) M) not only decreased basal formation of cyclic AMP (p < 0.05) but also attenuated the forskolin-stimulated increase of cyclic AMP (p < 0.005). The inhibitory effects of NPY on both basal levels of cyclic AMP and forskolin-induced increase of cyclic AMP were not reversed by the application of alpha-trinositol (10(-8)-10(-6) M). In studies on vasomotor responses, forskolin (10(-9)-10(-5) M) induced a concentration-dependent relaxation of precontracted guinea-pig basilar arteries. NPY (10(-7) M) shifted the forskolin-induced relaxation of the basilar arteries towards higher forskolin concentrations. This inhibitory effect of NPY was reversed by alpha-trinositol (10(-6) M). We conclude that 1) NPY decreases basal and forskolin-stimulated cyclic AMP levels; 2) alpha-trinositol neither reverses the inhibitory effect of NPY on nor modulates basal or forskolin-stimulated cyclic AMP levels; 3) However, the antagonistic effect of NPY on forskolin-induced relaxation is significantly reversed by administration of alpha-trinositol. This demonstrates a dissociation of the dilator effects of forskolin and its generation of cyclic AMP.

Topics: Adenylyl Cyclases; Animals; Basilar Artery; Cerebral Arteries; Colforsin; Cyclic AMP; Guinea Pigs; Inositol Phosphates; Male; Neuropeptide Y; Vasodilation

The modulatory effects of alpha-trinositol (D-myo-inositol-1.2.6- trisphosphate; PP 56) on the systemic arterial blood pressor responses induced by neuropeptide Y, preganglionic nerve stimulation, phenylephrine and vasopressin were studied in pithed rats. Intravenous administration (within 2 min.) of alpha-trinositol reduced the neuropeptide Y-induced increase in mean arterial pressure within a defined dose range without altering the heart rate. The influence of alpha-trinositol on the neuropeptide Y-induced pressor response in the presence of non-selective as well as H1- and H2-selective histamine antagonists (diphenhydramine, mepyramine and cimetidine respectively) were investigated. The maximal increase in mean arterial pressure induced by neuropeptide Y as well as the duration of the pressor response was enhanced after nonselective (diphenhydramine) or H1-selective (mepyramine) histamine blockade. The enhancement of the neuropeptide Y-induced pressor response by the H1 specific antagonist mepyramine was significantly more pronounced compared to the H2-selective agent. The exaggerated increase in mean arterial pressure in response to neuropeptide Y after histamine blockade was inhibited by alpha-trinositol to a similar extent as without such pretreatment. We conclude that neuropeptide Y interacts with histamine in the pithed rat and that this action may partially offset the pressor actions of the peptide. The neuropeptide Y-induced pressor responses may be inhibited by alpha-trinositol within a defined dose range indicating that this non-peptide agent may act as a functional inhibitor to neuropeptide Y in vascular tissue.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Cimetidine; Decerebrate State; Diphenhydramine; Electric Stimulation; Heart Rate; Histamine Antagonists; Injections, Intravenous; Inositol Phosphates; Male; Neuropeptide Y; Phenylephrine; Pyrilamine; Rats; Rats, Sprague-Dawley; Vasopressins

The effect of the neuropeptide Y antagonist D-myo-inositol-1,2, 6-trisphosphate (alpha-trinositol) was tested against modulatory actions mediated by neuropeptide Y in the isolated rat mesenteric arterial bed. Neuropeptide Y (1 and 10 nM) had no direct postjunctional effects, but augmented vasoconstrictor responses to noradrenaline and to sympathetic nerve stimulation to an extent which was greater with the higher concentration of neuropeptide Y. The augmenting effect of neuropeptide Y at 1 nM on vasoconstriction induced by lower doses of noradrenaline was antagonized by alpha-trinositol (1 microM), producing a shift to the right of the dose-response curve. A lower concentration of alpha-trinositol (0.1 microM) had no inhibitory effect on responses to noradrenaline. Augmentation by the higher concentration of neuropeptide Y (10 nM) of noradrenaline-induced vasoconstriction was not affected by alpha-trinositol at concentrations of up to 10 microM. alpha-Trinositol did not significantly antagonize neuropeptide Y-induced augmentation of vasoconstrictor responses to sympathetic nerve stimulation. alpha-Trinositol alone did not affect vasoconstrictor responses to noradrenaline, potassium, or to sympathetic nerve stimulation. In the raised-tone preparation (tone raised with methoxamine) in the presence of guanethidine (5 microM) to block sympathetic neuro-transmission, perivascular nerve stimulation caused vasodilatation due to activation of sensory-motor nerves. Neuropeptide Y inhibited sensory-motor nerve induced vasodilatation in a concentration-dependent manner but this was not affected by alpha-trinositol (1 microM). These results suggest that alpha-trinositol can be a useful functional antagonist of neuropeptide Y-induced augmentation of vasoconstrictor responses to noradrenaline in the rat mesenteric arterial bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Electric Stimulation; In Vitro Techniques; Inositol Phosphates; Male; Mesenteric Arteries; Motor Neurons; Muscle Contraction; Muscle, Smooth, Vascular; Neurons, Afferent; Neuropeptide Y; Norepinephrine; Rats; Rats, Wistar; Sympathetic Nervous System; Vasoconstriction; Vasodilation

Neuropeptide Y (NPY) induces contraction of guinea-pig basilar arteries via activation of Y1 receptors. This contraction is blocked by D-myo-inositol-1,2,6-triphosphate (alpha-trinositol). Previous binding studies have shown that alpha-trinositol has no effect at Y1 or Y2 binding sites thus the antagonistic effect should occur at the level of a second messenger. We have examined the effects of NPY on the formation of inositol phosphates (IP) and have looked for an antagonistic effect of alpha-trinositol. NPY (10(-9)-3 x 10-(-7) M) induced strong concentration-dependent contraction of basilar arteries from young guinea-pigs (weight 200-250 g) (Emax: 76.4 +/- 11.1%) but not of arteries from old guinea-pigs (weight > 500 g) (Emax: 2.8 +/- 1.5%). [Pro34]NPY and PYY induced contraction of similar magnitude and potency, whereas NPY13-36 had only a weak effect. This demonstrates an effect via the Y1 type of NPY receptor. The contraction induced by NPY was blocked by alpha-trinositol (p < 0.05). LiCI (2 x 10-4) M), used to inhibit IP breakdown, had no effect on the contraction induced by NPY. NPY (10(-10)-10(-8) M) increased the formation of IP in cerebral vessels from young guinea-pigs from 357 +/- 48 cpm/mg w.w. to 900 +/- 233 cpm/mg w.w. However, there was no alteration in IP formation in cerebral vessels from old guinea-pigs (NPY 10(-9)-10(-7) M). In the presence of alpha-trinositol (10(-8)-10(-6) M) the NPY induced stimulation of IP formation was totally abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Aging; Animals; Basilar Artery; Brain; Guinea Pigs; Inositol Phosphates; Neuropeptide Y; Vasoconstriction

The possibility that D-myo-inositol-1,2,6-triphosphate (PP56), which has shown some specificity for antagonism of neuropeptide Y (NPY) in vitro, may antagonize responses to sympathetic nerve stimulation was investigated in canine blood-perfused gracilis muscle in situ after pretreatment with irreversible alpha-adrenoceptor blockade by phenoxybenzamine and beta-adrenoceptor blockade by propranolol. Sympathetic nerve stimulation (10 Hz, 2 min) increased muscle perfusion pressure and evoked overflow of norepinephrine (NE) from the tissue. PP56 at 50 and 500 microM (calculated local arterial plasma concentrations) did not influence NE overflow but attenuated the late phase of the vasoconstrictor response to nerve stimulation and reduced the increase in perfusion pressure evoked by exogenous NPY. PP56 also induced vasodilatation per se, but had no effect on the vascular response to exogenous angiotensin II (AII) or the remaining vasoconstrictor response to exogenous NE. PP56 antagonizes late components in the nonadrenergic sympathetic vasoconstriction and vasoconstriction evoked by exogenous NPY, without influencing transmitter release. Because previous results with this and other models propose a role for NPY in mediating nonadrenergic vasoconstriction, we suggest that PP56 may antagonize effects of neuronally released NPY at the postjunctional level.

Topics: Analysis of Variance; Angiotensin II; Animals; Dogs; Electric Stimulation; Female; Inositol Phosphates; Neuropeptide Y; Norepinephrine; Phenoxybenzamine; Propranolol; Sympathetic Nervous System; Synaptic Transmission; Vasoconstriction

To investigate the cardiovascular effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate; PP56) in spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto (WKY) rats. alpha-Trinositol, a representative of a new group of pharmacological agents, is an inositol phosphate which seems to bind to a single population of binding sites, inhibiting, for example, agonist-induced vasoconstriction. In particular, alpha-trinositol seems to inhibit agonist-induced (e.g. neuropeptide Y-induced) elevations in intracellular Ca2+ levels in vascular smooth muscle cells.. alpha-Trinositol was administered as a bolus injection (2-40 mg/kg body weight), followed by a continuous infusion (20-400 mg/kg body weight per h) for 40 min in freely moving SHR and WKY rats.. Acute intravenous bolus administration of alpha-trinositol reduced systolic and diastolic blood pressure, as well as heart rate, in a dose-dependent manner in SHR and WKY rats. After completion of the 40-min infusion the reduction in blood pressure was more pronounced in the SHR than in the WKY control rats. Heart rate did not change in the SHR, whereas it was significantly increased at the highest dosage (400 mg/kg) in the WKY rats. At this dosage, three out of eight SHR died from cardiac arrhythmias after completing the infusion. The lowest dose of alpha-trinositol administered (2 mg/kg bolus followed by 20 mg/kg per h infusion over 40 min) significantly inhibited the increase in mean arterial pressure induced by neuropeptide Y (2 micrograms/kg per min for 10 min) by approximately 30% in both the SHR and WKY rats. Furthermore, alpha-trinositol treatment completely inhibited the potentiation induced by neuropeptide Y (0.1 micrograms/min for 30 min) of the blood pressure responses to intravenous bolus injections of noradrenaline (20 ng), tyramine (40 micrograms) or angiotensin II (10 ng).. Our results demonstrate that alpha-trinositol antagonizes the direct postsynaptic pressor response to exogenous neuropeptide Y, as well as the potentiating effects of neuropeptide Y on other vasoconstrictors in SHR and WKY rats. However, in the SHR alpha-trinositol lowered basal blood pressure only in the dose range which was non-specific for neuropeptide Y inhibition. Thus, the present study indicates that neuropeptide Y is involved only slightly in the maintenance of high blood pressure in SHR.

Topics: Animals; Blood Pressure; Dose-Response Relationship, Drug; Heart Rate; Hypertension; Inositol Phosphates; Male; Neuropeptide Y; Rats; Rats, Inbred SHR; Rats, Inbred WKY

PP56 (D-myo-inositol-1,2,6,-trisphosphate) has been reported to specifically inhibit neuropeptide Y-mediated effects in vasculature, heart and brain; because of its reversible but non-competitive antagonism interaction with neuropeptide Y receptor signalling or allosteric modulation of neuropeptide Y binding have been postulated. These possibilities were tested in the present study. PP56 did not affect [125I]neuropeptide Y binding to HEL- or SK-N-MC-cells or to porcine splenic membranes. PP56 did not inhibit neuropeptide Y-stimulated Ca2+ increases in HEL- or SK-N-MC-cells or in cultured porcine aortic vascular smooth muscle cells but if anything slightly enhanced it. PP56 did not antagonize the neuropeptide Y-mediated inhibition of forskolin-stimulated cAMP accumulation in HEL-cells. We conclude that previously reported antagonistic effects of PP56 occur distal to the neuropeptide Y receptor or its second messenger systems Ca2+ and cAMP or may be restricted to neuropeptide Y receptors in certain model systems.

Topics: Animals; Calcium; Cells, Cultured; Colforsin; Cyclic AMP; Inositol Phosphates; Muscle, Smooth, Vascular; Neuropeptide Y; Radioligand Assay; Receptors, Neuropeptide Y; Signal Transduction; Spleen; Swine

Perfusion of the rat mesenteric bed with 0.1 or 10 nM neuropeptide Y potentiated the noradrenaline-induced increase in mesenteric pressure; the peptide did not modify basal perfusion pressure. While perfusion with 0.1 nM neuropeptide Y significantly increased the maximal noradrenaline-evoked vasoconstriction without modifying its EC50, 10 nM neuropeptide Y potentiated the maximal noradrenaline effect and significantly shifted its concentration-response curve to the left. Perfusion with 1-10 microM D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol) reduced, in a concentration-dependent fashion, the neuropeptide Y-induced potentiation of the noradrenaline-evoked vasoconstriction without altering the potency or maximal response evoked by the catecholamine alone. Perfusion with 0.1 nM neuropeptide Y plus 1 microM alpha-trinositol completely abolished the neuropeptide Y-induced facilitation of the noradrenaline effect. alpha-Trinositol 1 microM in the presence of 10 nM neuropeptide Y caused a nonparallel rightward shift of the noradrenaline concentration-response curve as compared to that obtained in the presence of 10 nM neuropeptide Y alone. The alpha-trinositol blockade of the facilitatory action of neuropeptide Y was reversible.

Topics: Animals; Inositol Phosphates; Mesenteric Arteries; Neuropeptide Y; Norepinephrine; Perfusion; Rats; Rats, Sprague-Dawley; Vasoconstriction

The contribution of neurotransmitters known to be present in the cervical sympathetic nervous system to cerebral autoregulation was evaluated in the anaesthetised cat using a continuous measurement of cerebral cortical perfusion with laser Doppler flowmetry and an in vitro pial vessel preparation. Autoregulation was tested by venesection and fluid administration to achieve changes in blood pressure from -40% of resting control levels to +80% and flow was monitored. Between -20% and +50% there was no significant alteration in cortical blood flow with perfusion following blood pressure passively outside these ranges. The non-competitive neuropeptide Y antagonist PP56 shifted the level at which the change in flow was passively dependent on blood pressure from +60% to +38%. The pial vessel study demonstrated that PP56 shifted the dose-response curve for the vasoconstrictor effect of NPY with a maximal reduction of 22 +/- 6%. These data suggest that the cervical sympathetic nerves with NPY play an active role in cerebral autoregulation. Furthermore in view of the longer time course of action of neuropeptide Y, it is an ideal transmitter candidate to be involved in cerebral autoregulation and any compound that blocks its action must be considered to potentially alter the normal cerebrovascular physiology.

Topics: Animals; Blood Gas Analysis; Blood Pressure; Brain; Cats; Cerebrovascular Circulation; Dose-Response Relationship, Drug; Female; Heart Rate; Hemodynamics; Homeostasis; Inositol Phosphates; Laser-Doppler Flowmetry; Male; Muscle Contraction; Neuropeptide Y

Interactions between neuropeptide Y and perivascular vasodilator agents were studied in guinea pig cerebral, coronary, and uterine arteries. In all three types of arteries, vessel segments precontracted with prostaglandin F2 alpha or histamine relaxed concentration dependently upon application of acetylcholine (ACh), substance P (SP), and vasoactive intestinal peptide (VIP). Neuropeptide Y (NPY: 10(-8)-10(-7) M) caused inhibition of relaxations produced by ACh, SP, and VIP in all three types of segments; however, the effective concentration varied between vessel type. Thus, cerebral and uterine arteries were approximately 10 times more sensitive to NPY than the coronary artery. D-myo-inositol-1,2,6-triphosphate (PP56) was a potent inhibitor of the NPY effect in all three vessel types. Thus, NPY, which is colocalized not only with norepinephrine in sympathetic perivascular fibers but also with VIP and ACh in some parasympathetic neurons, can greatly reduce the vasodilatory effect of ACh and VIP, as well as of the sensory peptide SP. This further illustrates the complex interactions NPY has with perivascular neuroeffector mechanisms.

Topics: Animals; Cerebral Arteries; Coronary Vessels; Female; Guinea Pigs; In Vitro Techniques; Inositol Phosphates; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Neuropeptide Y; Sympathetic Nervous System; Uterus; Vasodilation

Pre- and postjunctional responses to nerve released or exogenous neuropeptide Y (NPY) were measured in the anaesthetised dog before and after administration of D-myo-inositol-1,2,6-trisphosphate (PP56) a putative NPY antagonist. The inhibition of the increase in pulse interval evoked by vagal stimulation was used as a measure of prejunctional action of NPY and the magnitude of increase in blood pressure was used as a measure of postjunctional action of NPY (direct action or constrictor potentiating). Elevated plasma levels of PP56 were maintained throughout the course of the experiment. PP56 significantly reversed the inhibitory effect of NPY (nerve released or exogenous) on cardiac vagal action, and significantly inhibited the pressor response to exogenous NPY. PP56 did not affect the pressor response to intravenous phenylephrine, a selective alpha-adrenoceptor agonist. PP56 therefore significantly antagonises both pre- and postjunctional effects of NPY (nerve released and exogenous) and, with respect to its postjunctional antagonism, this action is selective for NPY.

Topics: Anesthesia; Animals; Blood Pressure; Dogs; Electric Stimulation; Inositol Phosphates; Neuropeptide Y; Phenylephrine; Sympathetic Nervous System; Synapses; Vagus Nerve

Postganglionic sympathetic nerves release norepinephrine (NE) as their primary neurotransmitter at vascular and other targets. However, much evidence supports involvement of additional messengers, co-transmitters, which are co-released with NE upon sympathetic nerve stimulation and thereby contribute to their actions, e.g., vasoconstriction. Two such putative co-transmitters, neuropeptide Y (NPY) and adenosine triphosphate (ATP) have been of particular interest since they fulfill several neurotransmitter criteria. Importantly, hitherto it has been difficult to antagonize vasoconstriction evoked by either NPY or ATP with agents that are devoid of intrinsic activity. The present study describes the ability of a novel inositol phosphate, D-myo-inositol 1,2,6-trisphosphate (Ins[1,2,6]P3; PP-56) to in vitro potently block vasoconstrictor responses elicited by NPY and ATP, but not by NE, as studied in guinea-pig isolated basilar artery. The action of Ins[1,2,6]P3 does not seem to occur through antagonism at NPY- or ATP-receptor recognition sites, labeled by 125I-peptide YY and 35S-gamma-ATP, respectively, in membranes of rat cultured vena cava vascular smooth muscle cells. However, it does involve inhibition of the influx of Ca2+ induced by either co-transmitter in these same vena cava cells. It is proposed that Ins[1,2,6]P3 may be a useful functional antagonist of non-adrenergic component(s) of the vasoconstrictor response to sympathetic nerve stimulation.

Topics: Adenosine Triphosphate; Animals; Basilar Artery; Calcium; Cells, Cultured; Female; Guinea Pigs; Inositol Phosphates; Male; Muscle, Smooth, Vascular; Neuropeptide Y; Norepinephrine; Rats; Rats, Sprague-Dawley; Vasoconstriction; Vena Cava, Inferior

The effects of the proposed neuropeptide Y (NPY) antagonist, D-myo-inositol-1,2,6-triphosphate (PP56), on vasoconstrictor responses evoked by NPY and non-adrenergic sympathetic nerve stimulation were investigated in the pig in vivo. Under control conditions, exogenous NPY evoked a dose-dependent increase in arterial blood pressure and vasoconstriction in spleen, kidney and skeletal muscle. After administration of PP56 (50 mg/kg), which transiently reduced systemic blood pressure by 18 +/- 5 mm Hg, the vascular responses evoked by NPY did not differ from those observed under control conditions. Stimulation of the splenic nerve and the lumbar sympathetic chain with 20-Hz burst activity in reserpine-pretreated pigs, which are devoid of their noradrenaline content, decreased splenic and hindlimb vascular conductance by 67 +/- 7 and 57 +/- 7%, respectively, under control conditions. In the presence of PP56 the nerve stimulation-evoked reductions in splenic and hindlimb vascular conductance were slightly but not significantly reduced to 59 +/- 9 and 48 +/- 7%, respectively. It is concluded that PP56 in the presently used high dose, which causes non-selective inhibition of vasoconstriction in the rat, cannot be used as an antagonist of vasoconstrictor responses evoked by NPY or non-adrenergic sympathetic nerve stimulation in the pig.

Topics: Animals; Blood Pressure; Electric Stimulation; Hindlimb; In Vitro Techniques; Inositol Phosphates; Male; Neuropeptide Y; Regional Blood Flow; Renal Circulation; Reserpine; Spleen; Swine; Sympathetic Nervous System; Vasoconstriction

1. Although neuropeptide Y (NPY) is a potent vasoconstrictor in many vascular beds, nanomolar concentrations of this peptide potentiate the noradrenaline-induced contractions in rabbit gastroepiploic and femoral arteries, and guinea-pig mesenteric and uterine arteries. 2. The potentiating effect of NPY on noradrenaline-induced contraction was present in endothelium-denuded femoral arteries. 3. The potentiating effect of NPY on noradrenaline-induced contraction was antagonized by PP56 (D-myo-inositol 1,2,6-trisphosphate) in low concentrations (down to 0.1 nM). This antagonistic effect was observed in all four types of vessels studied. Contractions induced by noradrenaline, histamine, endothelin-1 and potassium were not altered by PP56 in concentrations upto 1 microM in femoral artery of rabbit. 4. We provide evidence that a non-peptide (PP56) can selectively antagonize NPY-induced effects in rabbit and guinea-pig peripheral arteries without affecting the vasoconstrictor response to noradrenaline.

Topics: Animals; Drug Synergism; Guinea Pigs; In Vitro Techniques; Inositol Phosphates; Male; Neuropeptide Y; Norepinephrine; Rabbits; Vasoconstriction; Vasoconstrictor Agents

The adrenergic cotransmitter neuropeptide Y (NPY) induces vascular smooth muscle contraction by occupying postsynaptic Y1 receptors and by enhancing the vasoconstriction induced by a series of other pressor agents. In particular, NPY modulates the blood pressure response to alpha-1 adrenergic agonists and angiotensin II. The inositol phosphate derivative, d-myo-inositol-1,2,6-trisphosphate (PP56), is a novel NPY antagonist which within a defined dose range selectively blocks the effects of exogenously administered NPY in vivo. In the pithed animal as well as in the freely moving Sprague-Dawley rat, an i.v. bolus administration of PP56 (2 mg/kg) followed by an infusion (20 mg/kg/hr for 30 min) inhibited the approximate 50% increase in mean arterial blood pressure induced by a continuous infusion of NPY (2 micrograms/kg/min for 10 min). Furthermore, PP56 treatment completely inhibited the enhancement induced by NPY (0.1 microgram/min for 50 min or 2 micrograms/kg/min for 10 min) of the pressor responses to preganglionic sympathetic nerve stimulation (in the pithed rat) and to i.v. bolus injections of noradrenaline (20 ng), the indirect sympathomimetic tyramine (40 micrograms) as well as to angiotensin II (10 ng). These results show that PP56, representing a new class of synthetic nonpeptide drugs, is capable of antagonizing the vascular smooth muscle contractile as well as the potentiating effects of NPY in vivo in the pithed as well as the conscious rat.

Topics: Angiotensin II; Animals; Blood Pressure; Brain; Drug Synergism; Injections, Intravenous; Inositol Phosphates; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Inbred Strains; Tyramine

It has been demonstrated that D-myo-inositol-1,2,6-trisphosphate (PP56) antagonizes the effect of neuropeptide Y (NPY) in guinea pig basilar arteries. NPY is known to inhibit insulin secretion. We therefore examined whether PP56 is a NPY antagonist also on insulin secretion. Unanaesthetized mice were injected intraperitoneally with PP56. It was found that the plasma insulin response to a subsequent intravenous glucose challenge (500 mg/kg) was inhibited by PP56 at 20 but not at 2 mg/kg. Also NPY (8.5 nmol/kg) inhibited the glucose-induced increase in plasma insulin levels. When given together, PP56 and NPY exerted additive inhibitory effect. Thus, PP56 is not a NPY-antagonist on insulin secretion, but rather exerts a NPY-like effect. Furthermore, in isolated mouse islets, PP56 at 100 nmol/l, but not at lower dose levels, inhibited glucose (11.1 mM)-stimulated insulin secretion. Hence, PP-56 inhibits glucose-stimulated insulin secretion by a direct effect on the pancreatic islets.

Topics: Animals; Depression, Chemical; Female; Glucose; Injections, Intraperitoneal; Inositol Phosphates; Insulin; Insulin Secretion; Islets of Langerhans; Mice; Neuropeptide Y; Secretory Rate

D-myo-Inositol-1,2,6-trisphosphate (PP56) is a novel experimental drug which is structurally related to the intracellular second messenger IP3. Among other pharmacological effects, PP56 has been shown to antagonize neuropeptide Y (NPY) induced vasoconstriction with a high degree of specificity. We examined the effects of i.c.v. PP56 on locomotor activity and food intake in rats, and on the hypoactivity and hyperphagia induced by NPY. In the open field, PP56 given alone increased locomotor activity by up to 85%. It did not prevent NPY induced hypoactivity to any extent. PP56 given alone did not affect food intake except for a small increase after the highest dose tested (200 nmol). When NPY was given after pretreatment with PP56, NPY induced hyperphagia was significantly reduced. A similar effect, however, was seen with regard to the hyperphagia produced by another orexigenic peptide, galanin. PP56 did not affect the binding of 125I-NPY to brain membranes in vitro, or to cells of two different neuroblastoma cell lines which selectively express NPY Y1 or Y2 receptors. In summary, PP56 acted as a locomotor stimulant per se. Only one of the two tested central effects of NPY could be antagonized by PP56, and then only partially and in a non-specific manner. The central effects of PP56 do not seem to be produced at the level of NPY receptors.

Topics: Animals; Behavior, Animal; Binding, Competitive; Brain; Eating; Humans; Hyperphagia; Immobilization; Injections, Intraventricular; Inositol Phosphates; Locomotion; Male; Membranes; Neuroblastoma; Neuropeptide Y; Rats; Rats, Inbred Strains; Receptors, Neuropeptide Y; Receptors, Neurotransmitter; Tumor Cells, Cultured

The antagonistic effects of a new inositol phosphate derivative, D-myoinositol-1,2,6-trisphosphate (PP56), on pressor responses to preganglionic sympathetic nerve stimulation and exogenously administered phenylephrine or neuropeptide Y (NPY) were investigated in vivo in the pithed rat. In this model an intravenous (i.v.) bolus administration of PP56 (1-50 mg/kg) dose dependently inhibited the increase in mean arterial blood pressure (MAP) induced by a continuous infusion of NPY (2 micrograms/kg per min for 10 min). PP56 in a dose of 5 mg/kg i.v. bolus reduced the entire NPY dose-response curve (0.4-8 microgram/kg per min 10 min infusion) without any shift to the right indicating a non-competitive interaction. Furthermore, PP56 (10-50 mg/kg i.v.) was found to inhibit the pressor response to preganglionic sympathetic nerve stimulation and i.v. bolus injection of the alpha 1-adrenoceptor agonist, phenylephrine. The dose-response curves for increasing doses of phenylephrine and incremental preganglionic sympathetic nerve stimulation were not significantly altered by a lower dose of PP56 (5 mg/kg i.v. bolus). We conclude that PP56, representing a new class of synthetic drugs, can antagonize the actions of exogenous and endogenous NPY in vivo, an action which is specific for NPY within a limited dose range.

Topics: Analysis of Variance; Animals; Blood Pressure; Decerebrate State; Dose-Response Relationship, Drug; Electric Stimulation; Inositol Phosphates; Male; Neuropeptide Y; Phenylephrine; Probability; Rats; Rats, Inbred Strains; Sympathetic Nervous System

Topics: Animals; Blood Pressure; Drug Synergism; Hypertension; Inositol Phosphates; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY

Neuropeptide Y (NPY) potentiates noradrenaline (NA)-evoked constriction of circular segments of the rabbit femoral artery. The potentiation occurs exclusively in the lower concentration-range of the agonist NA (10(-8)-3 x 10(-7) M) without any change in maximum contractile effect. NPY per se is without contractile effect in the rabbit femoral artery. The recently developed substance, D-myo-inositol-1.2.6-trisphosphate (PP56), which is an isomer of inositol-1.4.5-trisphosphate, is without effect per se on the rabbit femoral artery, nor does it affect NA-induced contractions. However, it was found to completely antagonize NPY-induced potentiation of the NA concentration-response curve.

Topics: Animals; Drug Synergism; Femoral Artery; In Vitro Techniques; Inositol Phosphates; Male; Neuropeptide Y; Norepinephrine; Rabbits; Vasoconstrictor Agents

The antagonistic properties on neuropeptide Y (NPY)-induced contraction of the guinea pig basilar artery of D-myo-inositol-1.2.6-triphosphate (PP56) has been examined using a sensitive in vitro system. It was observed that PP56 did not per se cause contraction or relaxation of precontracted vessel segments. However, it was found to be a non-competitive antagonist of NPY-induced contraction. This effect was observed in the concentration range 10(-8)-10(-6) M PP56. A slight potentiation of endothelin I-induced contraction was seen at high concentrations (10(-3) M). In contrast there was no modulation of the contractile effects elicited by bradykinin, noradrenaline, 5-hydroxytryptamine (5-HT) or prostaglandin F2 alpha (PGF2 alpha) apart from a slight reduction in maximum effect at 10(-4) M and 10(-3) M PP56. PP56 was observed to possess antihistaminic and anticholinergic properties in the concentration range 10(-5) M-10(-3) M. The relaxant effects of vasoactive intestinal peptide, calcitonin gene-related peptide, neurokinin A and substance P were only modified to a minor extent by PP56 in concentrations of 10(-4) M and 10(-3) M. In conclusion, PP56 appears to be the first non-peptide which potently and rather selectively antagonizes NPY-induced contractions of the guinea pig basilar artery. In high concentrations, PP56 may modify the responses of other agents tested, including histamine and acetylcholine.

Topics: Acetylcholine; Animals; Basilar Artery; Bradykinin; Calcitonin Gene-Related Peptide; Dinoprost; Endothelins; Female; Guinea Pigs; Histamine; Inositol Phosphates; Male; Muscle Contraction; Muscle, Smooth, Vascular; Neuropeptide Y; Norepinephrine; Serotonin; Tachykinins; Vasoactive Intestinal Peptide; Vasoconstriction; Vasodilation