guanylyl-imidodiphosphate and Disease-Models--Animal

Adenosine is an inhibitory modulator of neuronal activity and its possible involvement in seizures is of interest. We have examined changes in adenosine, its metabolites and receptors in brains of hippocampus-kindled rats, a model of partial epilepsy. Purine levels were measured by in vivo microdialysis and showed a small increase in adenosine and a dramatic increase in its metabolites after kindled seizures. Adenosine A1 receptor binding using [H]DPCPX was unaltered after seizures, whereas A1 agonist stimulated binding of GTP[gamma-S] and A1 mRNA expression increased in the CA3 and other regions. Striatal adenosine A2A mRNA and receptor binding with [H]SCH-58261 decreased. These findings indicate that kindled seizures increase adenosine release and metabolism and induces adaptive changes in adenosine receptors.

Topics: Animals; Autoradiography; Binding Sites; Brain Chemistry; Carrier Proteins; Corpus Striatum; Disease Models, Animal; Gene Expression Regulation; Guanosine 5'-O-(3-Thiotriphosphate); Guanylyl Imidodiphosphate; Hippocampus; In Situ Hybridization; Kindling, Neurologic; Male; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Purines; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2A; Receptors, Purinergic P1; Seizures; Sulfur Isotopes; Tritium; Xanthines

The purpose of the present study was to characterize alterations in the adenylyl cyclase (AC), cyclic adenosine 3',5'-monophosphate (cAMP), and spatial memory function after sustained cerebral ischemia. Sustained cerebral ischemia was induced by injection of 900 microspheres (48 microm in diameter) into the right (ipsilateral) hemisphere of rats. Alterations in the AC and cAMP in the cerebral cortex and hippocampus were examined up to 7 days after the embolism. A decrease in the cAMP content was seen in the ipsilateral hemisphere throughout the experiment. Microsphere embolism (ME) decreased the activity of Ca(2+)/calmodulin (CaM)-sensitive AC in the ipsilateral hemisphere throughout the experiment, whereas the basal and 5'-guanylyl imidodiphosphate (Gpp(NH)p)-sensitive AC activities were not altered. Immunoblotting analysis of AC subtypes with specific antibodies showed a decrease in the immunoreactivity of AC-I in the ipsilateral hemisphere during these periods. No significant differences in the immunoreactivity of AC-V/VI and AC-VIII were observed after ME. The levels of GTP-binding proteins Galpha(s), Galpha(i), and Gbetawere unchanged. Furthermore, microsphere-embolized rats showed prolongation of the escape latency in the water maze task determined on the seventh to ninth day after the operation. These results suggest that sustained cerebral ischemia may induce the impairment of the AC, particularly a selective reduction in the AC-I level and activity, coupled with the decrease in cAMP content. This reduction may play an appreciable role in the disturbance in cAMP-mediated signal transduction system, possibly leading to learning and memory dysfunction.

Topics: Adenylyl Cyclases; Animals; Brain Ischemia; Calcium; Carotid Artery Thrombosis; Cerebral Cortex; Cerebral Infarction; Cyclic AMP; Disease Models, Animal; Down-Regulation; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Hippocampus; Intracranial Embolism and Thrombosis; Isoenzymes; Male; Maze Learning; Memory Disorders; Microspheres; Rats; Rats, Wistar; Signal Transduction; Telencephalon

Congestive heart failure is associated with cardiac adrenergic nerve terminal changes and beta-adrenoceptor density downregulation. To study the temporal sequence of these changes, we performed studies in rabbits at 2, 4, and 8 wk of cardiac pacing (360 beats/min) and at 1, 2, and 4 wk after cessation of pacing. Rapid pacing produced left ventricular (LV) dysfunction and an increase in plasma norepinephrine (NE) in 1-2 wk. At week 2, NE uptake activity, NE uptake-1 density, and adenylyl cyclase responses to isoproterenol, 5'-guanylyl imidodiphosphate [Gpp(NH)p], and forskolin reduced. However, immunostained tyrosine hydroxylase profile, beta-adrenoceptor density, and NE histofluorescence did not reduce until 4-8 wk of pacing. After cessation of cardiac pacing, LV function normalized quickly, followed by return of tyrosine hydroxylase and NE profiles in 1 wk and adenylyl cyclase responses to agonists and NE uptake activity in 2 wk. Myocardial beta-adrenoceptor density returned to normal by 4 wk after cessation of pacing. Our results suggest that there is no permanent structural neuronal damage in the myocardium within the first 8 wk of rapid cardiac pacing. Abnormal myocardial NE reuptake mechanism may play an important pathophysiological role in heart failure.

Topics: Adenylyl Cyclases; Adrenergic beta-Agonists; Animals; Binding Sites; Cardiac Pacing, Artificial; Colforsin; Disease Models, Animal; Down-Regulation; Guanylyl Imidodiphosphate; Heart Failure; Hemodynamics; Myocardium; Nerve Endings; Norepinephrine; Rabbits; Receptors, Adrenergic, beta; Sympathetic Nervous System; Tyrosine 3-Monooxygenase; Ventricular Function, Left

Desensitization of the beta-adrenergic receptor (beta-AR) response is well documented in hypertrophied hearts. We investigated whether beta-AR desensitization is also present at the cellular level in hypertrophied myocardium, as well as the physiological role of inhibitory G (G(i)) proteins and the L-type Ca(2+) channel in mediating beta-AR desensitization. Left ventricular (LV) myocytes were isolated from hypertrophied hearts of hypertensive Dahl salt-sensitive (DS) rats and nonhypertrophied hearts of normotensive salt-resistant (DR) rats. Cells were paced at a rate of 300 beats/min at 37 degrees C, and myocyte contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) were simultaneously measured. In response to increasing concentrations of isoproterenol, DR myocytes displayed a dose-dependent augmentation of cell shortening and the [Ca(2+)](i) transient amplitude, whereas hypertrophied DS myocytes had a blunted response of both cell shortening and the [Ca(2+)](i) transient amplitude. Interestingly, inhibition of G(i) proteins did not restore beta-AR desensitization in DS myocytes. The responses to increases in extracellular Ca(2+) and an L-type Ca(2+) channel agonist were also similar in both DS and DR myocytes. Isoproterenol-stimulated adenylyl cyclase activity, however, was blunted in hypertrophied myocytes. We concluded that compensated ventricular hypertrophy results in a blunted contractile response to beta-AR stimulation, which is present at the cellular level and independent of alterations in inhibitory G proteins and the L-type Ca(2+) channel.

Topics: Adenylate Cyclase Toxin; Adenylyl Cyclases; Adrenergic beta-Agonists; Animals; Calcium; Calcium Channel Agonists; Calcium Channels, L-Type; Disease Models, Animal; Dose-Response Relationship, Drug; GTP-Binding Protein alpha Subunits, Gi-Go; Guanylyl Imidodiphosphate; Heart Function Tests; Hypertrophy, Left Ventricular; In Vitro Techniques; Isoproterenol; Male; Manganese; Myocardial Contraction; Myocardium; Rats; Rats, Inbred Dahl; Receptors, Adrenergic, beta; Signal Transduction; Virulence Factors, Bordetella

Bovine hereditary cardiomyopathy (bCMP) displays clinical characteristics of human idiopathic dilated cardiomyopathy (DCM). We studied isometric force of contraction in right ventricular trabeculae, plasma and tissue catecholamines, beta- and alpha 1-adrenoceptor density, Gi proteins and adenylyl cyclase activity in eight hearts with bCMP and eight control hearts (right and left atria and ventricles each).. Compared to control, the potency of isoprenaline in bCMP was eight-fold decreased, whereas the maximal positive inotropic effect of isoprenaline as well as the efficacy and potency of calcium were unchanged. Plasma noradrenaline was increased by 240%. Tissue noradrenaline and adrenaline were decreased by 36-63% and 58-69%, whereas dopamine was increased by 105-218%. beta-adrenoceptor density was drastically reduced by 90%, but binding affinity was unchanged. alpha-Adrenoceptor density and binding affinity were unchanged. Total PTX-substrates were increased in bCMP by 28-99%. Basal adenylyl cyclase activity was decreased by 36-47%. Similarly, stimulation by GTP, GMPPNP, isoprenaline, sodium fluoride, manganese or forskolin was attenuated by 26-62% (atria) and 45-66% (ventricles). In conclusion, we found marked activation of the sympatho-adrenergic system, downregulation of beta-adrenoceptors, upregulation of Gi proteins, global desensitization of adenylyl cyclase and selective subsensitivity to beta-adrenergic inotropic stimulation. These results closely resemble the characteristic alterations in the beta-adrenoceptor-G protein-adenylyl cyclase pathway in human heart failure, indicating that they are general features of heart failure. The similarity to human DCM, the inheritance and the availability of large tissue samples make bCMP a suitable model for human DCM.

Topics: Adenylate Cyclase Toxin; Adenylyl Cyclases; Animals; Cardiomyopathies; Cardiomyopathy, Dilated; Catecholamines; Cattle; Cattle Diseases; Colforsin; Disease Models, Animal; GTP-Binding Proteins; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Heart; Heart Atria; Heart Ventricles; Humans; Isoproterenol; Manganese; Myocardial Contraction; Myocardium; Receptors, Adrenergic, alpha-1; Receptors, Adrenergic, beta; Reference Values; Sodium Fluoride; Ventricular Function, Right; Virulence Factors, Bordetella

A genetic model of airway hyperreactivity has been described in which strains of mice are hyperresponsive (A/J) or hyporesponsive (C3H/HeJ) to intravenous acetylcholine challenge. To determine the mechanism of this differential responsiveness, we compared beta 2-adrenergic and muscarinic cholinergic receptor properties and their coupling to guanine nucleotide binding proteins (G proteins) in peripheral lung membrane fractions from these strains. No significant differences were found between the strains with regard to beta 2-adrenergic or muscarinic receptor density or antagonist affinity. No strain difference was found in beta 2-adrenergic receptor affinity for isoproterenol in the presence or absence of the nonhydrolyzable guanine nucleotide 5'-guanylimidodiphosphate [Gpp(NH)p]. In contrast, affinity of the high-affinity carbachol binding site of muscarinic receptors was threefold greater in A/J lung compared with C3H/HeJ lung (pKH = 7.34 +/- 0.16 vs. 6.79 +/- 0.06, respectively, P < 0.05). In the presence of Gpp(NH)p, this affinity was decreased sevenfold in A/J lung but was not significantly affected in C3H/HeJ lung, suggesting that muscarinic receptors in A/J lung are more effectively coupled to G proteins. Levels of Gs alpha and Gi alpha proteins in peripheral lung were significantly greater in the A/J strain compared with the C3H/HeJ strain (40 and 20% greater, respectively). These studies suggest that airway hyperreactivity in A/J mice is not associated with alterations in beta 2-adrenoceptors, but may be a result of enhanced muscarinic receptor signal transduction due to increased agonist affinity for muscarinic receptors and upregulation of G protein levels.

Topics: Animals; Binding, Competitive; Bronchial Hyperreactivity; Cell Membrane; Dihydroalprenolol; Disease Models, Animal; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Isoproterenol; Kinetics; Lung; Male; Mice; Mice, Inbred A; Mice, Inbred C3H; Molecular Weight; Quinuclidinyl Benzilate; Receptors, Adrenergic, beta-2; Receptors, Muscarinic; Species Specificity

Leukotriene (LT) D4 receptor in the granulation tissue formed in the air pouch-type allergic inflammation model in rats was analyzed. Membrane preparation of the granulation tissue obtained 3-9 days after the antigen challenge has specific binding sites of [3H]LTD4. Scatchard analysis showed that the affinity (Kd) and the density (Bmax) were not changed among the granulation tissue obtained 3-9 days after the antigen challenge. The Kd value in the granulation tissue (0.90 +/- 0.12 nM) was close to that in the rat lung (1.00 +/- 0.24 nM) and the guinea pig lung (0.86 nM). On the other hand, Bmax (62 +/- 8 fmol/mg protein) in the granulation tissue was higher than that in the rat lung (21 +/- 4 fmol/mg protein) but was far less than that in the guinea pig lung (405 fmol/mg protein). LTC4 and LTE4 inhibited the binding of [3H]LTD4 to the membrane preparation of the granulation tissue in a concentration-dependent manner. IC50 of LTC4 and LTE4 were 1 x 10(-7) and 2 x 10(-7) M, respectively. A guanine nucleotide, guanyl-5'-yl-imido-diphosphate (GppNHp), reduced [3H]LTD4 binding to the membrane preparation of the granulation tissue suggesting that LTD4 receptors in the granulation tissue are associated with G proteins. These results indicate that LTD4 binding sites in the granulation tissue are high affinity receptors for LTD4. A possible role of LTD4 in the recurrence of allergic inflammation in the chronic phase is discussed.

Topics: Animals; Asthma; Bronchial Hyperreactivity; Bronchitis; Cell Membrane; Disease Models, Animal; Granulation Tissue; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Leukotriene E4; Male; Rats; Rats, Sprague-Dawley; Receptors, Immunologic; Receptors, Leukotriene; Specific Pathogen-Free Organisms; SRS-A

Catecholamine therapy is often ineffective in reversing the peripheral vasodilatation and hypotension of septic shock. This suggests that catecholamines might not be able to activate alpha 1-adrenergic receptors to cause vasoconstriction. Despite elevations in endogenous catecholamines, hypoglycemia is also a complication of human sepsis, suggesting that among many other causes, hepatic alpha 1-receptors might be altered. To better understand the pathophysiologic basis for this pharmacologic dilemma, we studied the effect of experimental sepsis on alpha 1-adrenergic receptors in hepatic tissue, a rich source of alpha 1-receptors, from septic and control Sprague-Dawley rats. alpha 1-adrenergic receptors were measured with [3H]-prazosin and data analyzed by a computerized nonlinear least-square regression algorithm. Twenty-four hours following cecal ligation with puncture, a decreased number of alpha 1-adrenergic receptors was noted in crude and purified plasma membrane fractions (23 and 40% reductions respectively) from septic animals. No changes in either agonist or antagonist affinity for receptors from septic animals were noted. These data indicate that the catecholamine refractoriness seen in septic shock may be a result of alterations in alpha 1-adrenergic receptor number or receptor-effector coupling.

Topics: Animals; Bacterial Infections; Chronic Disease; Dihydroergotoxine; Disease Models, Animal; Glucose; Guanylyl Imidodiphosphate; In Vitro Techniques; Kinetics; Liver; Male; Prazosin; Rats; Rats, Inbred Strains; Receptors, Adrenergic, alpha; Shock, Septic; Tritium

We studied the alterations in myocardial beta-adrenergic receptor-adenylate cyclase activity and muscarinic receptor density in a canine model of left ventricular (LV) failure. LV failure was characterized by a doubling of LV weight/body weight ratio (3.3 +/- 0.1 to 6.9 +/- 0.4 g/kg) and an elevation of LV end-diastolic pressure, 32 +/- 4.5 mmHg, compared with 7.7 +/- 0.6 mmHg in normal dogs. Despite a 44% increase in receptor density as measured by antagonist binding studies with [3H]dihydroalprenolol, there was a twofold decrease in receptor affinity, i.e., an increase in the dissociation constant (Kd) (5.6 +/- 0.7 to 12 +/- 1.6 nM) in heart failure. Agonist displacement of [3H]dihydroalprenolol binding with isoproterenol in the presence and absence of 5'-guanylylimidodiphosphate [Gpp(NH)p] demonstrated a striking loss of high affinity binding sites in heart failure (51 +/- 16 to 11 +/- 5%). Beta-Adrenergic receptor-mediated stimulation of adenylate cyclase and maximal stimulation with Gpp(NH)p or sodium fluoride was reduced in heart failure. There was a concomitant marked, P less than 0.01, reduction in muscarinic receptor density (242 +/- 19 vs. 111 +/- 20 fmol/mg). Thus, while muscarinic receptor density fell, beta-adrenergic receptor density actually increased in LV failure. However, a larger portion of the beta-adrenergic receptors are not functionally coupled to the GTP-stimulatory protein (Ns), as evidenced by a decrease in the fraction of receptors that bind agonist with high affinity.

Topics: Adenylyl Cyclases; Animals; Disease Models, Animal; Dogs; Female; Guanylyl Imidodiphosphate; Heart Failure; Isoproterenol; Male; Myocardium; Norepinephrine; Receptors, Adrenergic, beta; Receptors, Muscarinic; Sodium-Potassium-Exchanging ATPase

Experimental obesity syndromes are characterized by considerable fat accretion which may be the result of hyperinsulinemia. Adipose tissue accretion may be the result both of the excessive synthesis of triglycerides and a defect in their mobilization from adipose tissue stores. The adenylate cyclase system which appears to be the site of the defect in mobilization is studies in more detail.

Topics: Adenylyl Cyclases; Adipose Tissue; Animals; Cell Membrane; Disease Models, Animal; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Kinetics; Lipolysis; Liver; Mice; Mice, Obese; Obesity; Rats; Rats, Inbred Strains; Rats, Zucker