guanosine-triphosphate and Hypertension

Serotonin (5-hydroxytryptamine, 5-HT) binds to numerous cognate receptors to initiate its biological effects. In this review, we have focused on the 5-HT2B receptor to address how signaling and expression of this receptor is specifically implicated in embryonic development and adult health and disease. Transduction of the 5-HT2B signaling is complex, including phospholipase C and A2 stimulation, cGMP production and a mitogenic signal that integrates the tyrosine kinase-signaling pathway. Furthermore, 5-HT, through the 5-HT2B receptors, has the ability to control serotonergic differentiation of committed neuron-like cells. In addition, 5-HT2B receptors are actively involved in the transient action of 5-HT during embryonic morphogenesis. Our recent data presented the first genetic evidence that 5-HT via 5-HT2B receptors regulates cardiac embryonic development and adult functions and suggested that this receptor subtype may be involved in other physiopathological situations. In particular, 5-HT-dependent molecular mechanisms may be involved in embryonic development and postnatal maturation of the enteric nervous system. Also, the involvement of the 5-HT2B receptor in the vascular growth often observed in hypertension is likely. These probably result from reactivation of developmentally regulated receptors in pathological situations. Finally, embryonic functions of 5-HT2 receptors observed in Drosophila gastrulation suggest evolutionary conserved mechanisms.

Topics: Animals; Calcium; Cell Differentiation; Drosophila melanogaster; Embryonic and Fetal Development; Enteric Nervous System; Evolution, Molecular; Fetal Heart; Fetal Proteins; Gastrula; Gene Expression Regulation, Developmental; Guanosine Triphosphate; Humans; Hypertension; Mammals; MAP Kinase Signaling System; Mice; Mice, Knockout; Morphogenesis; Nerve Tissue Proteins; Protein Kinase C; Receptor, Serotonin, 5-HT2B; Receptors, Serotonin; Serotonin; Signal Transduction; Species Specificity; Type C Phospholipases

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder whose major feature is the occurrence of multiple neurofibromas, which are benign tumors of the nerve sheath. It affects an estimated one in 3000 to 4000 individuals. In addition to neurofibromas, there are many other clinical manifestations, including malignant tumors such as gliomas or malignant peripheral nerve sheath tumors, and nontumor effects such as skeletal dysplasia and learning disability. Diagnosis is established on the basis of clinical criteria. Molecular genetic testing is feasible, but the large size of the gene and wide range of pathogenic mutations have so far impeded the development of a clinical diagnostic test. Insights into pathogenesis have followed from identification of the NF1 gene and the development of animal models. The major function of the gene product appears to be regulation of the ras protein. Tumors are believed to arise by the loss of function of the NF1 protein, suggesting that NF1 behaves as a tumor suppressor gene. Heterozygous effects on some cell types are also likely, however. The role of ras in the pathogenesis of tumors in NF1 has suggested an approach to treatment using ras inhibitors, some of which are likely to begin in clinical trials in NF1 patients in the near future.

Topics: Animals; Brain Neoplasms; Cafe-au-Lait Spots; Cell Transformation, Neoplastic; Female; Genes, Dominant; Genes, Neurofibromatosis 1; Glioma; Guanosine Triphosphate; Humans; Hypertension; Learning Disabilities; Leukemia; Male; Mice; Mice, Knockout; Neurofibroma; Neurofibromatosis 1; Neurofibromin 1; Protein Structure, Tertiary; ras Proteins; Rhabdomyosarcoma; Scoliosis

The Sabra hypertension resistant rats (SBN) have an outstanding ability to maintain normal blood pressure when exposed to procedures that ordinarily cause hypertension in normal rats. The following findings may be relevant to resistance to hypertension of these rats: 1) In SBN rats, cardiac norepinephrine content is not affected by DOCA-salt treatment. Since depletion of cardiac norepinephrine is an index of cardiac adrenergic nerve overactivity, the results suggest an attenuated cardiac sympathetic nerve activity in these rats. 2) In SBN rats, the sensitivity of the baroreflex control of the heart is markedly increased compared with other strains. Reduction of baro-receptor sensitivity by aortic-baroreceptor deafferentation renders them susceptible to DOCA-salt hypertension. The results suggest a strong relationship between baroreflex supersensitivity and resistance to hypertension in these rats. 3) The amount of alpha 2 adrenoreceptor densities in cerebral and renal cortical membranes of normal rats increased in vitro, in the presence of sodium and guanyl nucleotide (GTP). In SBN rats, the effect of sodium is markedly attenuated compared with SBH, while response to GTP is identical in the two strains. The demonstration of a similar pattern of response in the Dahl rats suggests that alpha 2 adrenoreceptor may be involved in the sensitivity or resistance to salt induced hypertension.

Topics: Animals; Desoxycorticosterone; Guanosine Triphosphate; Hypertension; Pressoreceptors; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Receptors, Adrenergic, alpha; Sodium Chloride; Sympathetic Nervous System

An untargeted multi-omics study implicated the potential dysregulation of fatty acid, nucleotide, and energy metabolism in the brainstems of spontaneously hypertensive rats (SHRs). A further quantitative exploration of the alterations in the metabolic pathways is necessary for a deep understanding of the central nervous system in SHRs. Targeted metabolic profiling of 40 fatty acids (PeptideAtlas: PASS01671) and 32 metabolites of nucleotides and energy metabolism (PeptideAtlas: PASS01672) and parallel reaction monitoring analysis of 5 proteins (PeptideAtlas: PASS01673) were performed on the brainstems of SHRs (

Topics: Animals; Brain Stem; Fatty Acids, Unsaturated; Guanosine Triphosphate; Hypertension; Rats; Rats, Inbred SHR; Rats, Wistar

The peripheral dopaminergic system plays a crucial role in blood pressure regulation through its actions on renal hemodynamics and epithelial ion transport. The dopamine D5 receptor (D(5)R) interacts with sorting nexin 1 (SNX1), a protein involved in receptor retrieval from the trans-Golgi network. In this report, we elucidated the spatial, temporal, and functional significance of this interaction in human renal proximal tubule cells and HEK293 cells stably expressing human D(5)R and in mice. Silencing of SNX1 expression via RNAi resulted in the failure of D(5)R to internalize and bind GTP, blunting of the agonist-induced increase in cAMP production and decrease in sodium transport, and up-regulation of angiotensin II receptor expression, of which expression was previously shown to be negatively regulated by D(5)R. Moreover, siRNA-mediated depletion of renal SNX1 in C57BL/6J and BALB/cJ mice resulted in increased blood pressure and blunted natriuretic response to agonist in salt-loaded BALB/cJ mice. These data demonstrate a crucial role for SNX1 in D(5)R trafficking and that SNX1 depletion results in D(5)R dysfunction and thus may represent a novel mechanism for the pathogenesis of essential hypertension.

Topics: Animals; Cell Membrane; Cyclic AMP; Fluorescence Resonance Energy Transfer; Gene Expression Regulation; Gene Silencing; Guanosine Triphosphate; HEK293 Cells; Humans; Hypertension; Kidney Tubules, Proximal; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Models, Biological; Receptors, Dopamine D5; RNA Interference; Sorting Nexins

The mechanisms of exercise-induced health benefits are complex and not fully understood. This study investigated the effects of exercise and hypertension on cardiovascular hemodynamic responses and red blood cell (RBC) concentrations of purine nucleotides using normotensive and hypertensive rat models in vivo.. Sprague Dawley rats (SDRs) and spontaneously hypertensive rats (SHRs) were exercised on a treadmill for 15 min at a speed of 10 m/min and 5% grade. Blood samples were obtained from each rat before, during, and after exercise for measurement of adenosine 5'-triphosphate (ATP) and guanosine 5'-triphosphate (GTP) concentrations in RBCs by a validated high-performance liquid chromatography assay. They were returned to a restrainer after exercise, and hemodynamic recording collected continuously up to 6 h. Two separate groups (SDRs and SHRs) without exercise were used as controls. Biomarker data were compared between SDRs and SHRs using analysis of variance and t test and difference considered significant at p < 0.05.. The study has demonstrated for the first time a difference in the postexercise effect between SDRs and SHRs. The 15 min of exercise significantly increased systolic blood pressure (SBP) (129 ± 16 to 162 ± 26 mmHg) and heart rate (HR) (416 ± 29 to 491 ± 26 bpm) in SDRs (p < 0.05), but not in SHRs. The postexercise hemodynamic effects were more profound in SHRs. SBP and diastolic blood pressure (DBP) also fell significantly in the control group of SHRs (SBP 184 ± 14 to 152 ± 29 mmHg and DBP 149 ± 9 to 120 ± 14 mmHg, p < 0.05 for both) towards the end of the experiment but not in the SDR group. The RBC concentrations of ATP and GTP increased after exercise in both SDRs and SHRs which were significantly correlated with the postexercise hemodynamic effect (p < 0.05).. SHRs were more tolerant to increases in HR and SBP induced by exercise, and have more profound postexercise hemodynamic effects than SDRs. The hemodynamic effects were linked closely with RBC concentrations of ATP and GTP in both SDRs and SHRs.

Topics: Adaptation, Physiological; Adenosine Triphosphate; Animals; Blood Pressure; Chromatography, High Pressure Liquid; Disease Models, Animal; Erythrocytes; Exercise Test; Guanosine Triphosphate; Heart Rate; Hemodynamics; Hypertension; Male; Physical Exertion; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Time Factors; Up-Regulation

In male coupling factor 6 (CF6)-overexpressing transgenic (TG) mice, a high-salt diet induces hypertension and cardiac systolic dysfunction with excessive reactive oxygen species generation. However, the role of gender in CF6-mediated pathophysiology is unknown. We investigated the effects of ovariectomy and estrogen replacement on hypertension, cardiac dysfunction and Rac1 activity, which activates radical generation and the mineralocorticoid receptor, in female TG mice. Fifteen-week-old male and female TG and wild-type (WT) mice were fed a normal- or high-salt diet for 60 weeks. Systolic and diastolic blood pressures were higher in the TG mice fed a high-salt diet than in those fed a normal-salt diet at 20-60 weeks in males but only at 60 weeks in females. The blood pressure elevation under high-salt diet conditions was concomitant with a decrease in left ventricular fractional shortening. In the WT mice, neither blood pressure nor cardiac systolic function was influenced by a high-salt diet. In the female TG mice, bilateral ovariectomy induced hypertension with cardiac systolic dysfunction 8 weeks after the initiation of a high-salt diet. The ratios of Rac1 bound to guanosine triphosphate (Rac1-GTP) to total Rac1 in the heart and kidneys were increased in the ovariectomized TG mice, and estrogen replacement abolished the CF6-mediated pathophysiology induced under the high-salt diet conditions. The overexpression of CF6 induced salt-sensitive hypertension, complicated by systolic cardiac dysfunction, but its onset was delayed in females. Estrogen has an important role in the regulation of CF6-mediated pathophysiology, presumably via the downregulation of Rac1.

Topics: Animals; Estrogens; Female; Guanosine Triphosphate; Hypertension; Kidney; Male; Mice; Mice, Transgenic; Mitochondrial Proton-Translocating ATPases; Myocardium; Neuropeptides; Ovariectomy; Oxidative Phosphorylation Coupling Factors; rac GTP-Binding Proteins; rac1 GTP-Binding Protein; Sex Factors; Sodium Chloride, Dietary; Ventricular Dysfunction, Left

The inhibitory GTP-binding protein (Gi protein) plays an important role in regulation of vascular tone. Many studies have implicated the role of Gi protein in conduit vessels. However, the physiological role of Gi protein in the control of peripheral microvascular tone in hypertension has not been established yet. Therefore, we investigated the concentration of Gi protein in the peripheral resistance arteries and aorta in the spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY) and renovascular hypertensive rats (RHR), using immunohistochemical methods semiquantitatively. Changes in the function of Gi protein in relation to alpha2-adrenoceptor were also investigated by microcannulation techniques. We have shown that the amount of alpha2 subunits of Gi protein in the cremaster small artery was significantly lower in SHR aged 4 weeks and older than in age-matched WKY and that there were no significant differences between RHR and WKY. We also demonstrated that the function of Gi protein in relation to alpha2-adrenoceptor was already lower in SHR before the onset of hypertension. The quantitative and functional decline in Gi protein in the smooth muscle cells of peripheral small arteries were observed in SHR even before the onset of hypertension, whereas rats with secondary hypertension did not exhibit this finding.

Topics: Aging; Animals; Arteries; GTP-Binding Protein alpha Subunits, Gi-Go; Guanosine Triphosphate; Hypertension; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, alpha-1

In the present studies, we have investigated if aorta, like heart from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, (HR) also exhibit enhanced expression of G-protein levels and if these alterations occur before or after the development of blood pressure.. Sprague-Dawley rats treated with DOCA-salt or vehicle for 1, 2, 3 and 4 weeks were used for these studies. The levels of inhibitory guanine nucleotide regulatory proteins (Gi alpha-2, Gi alpha-3) and G beta proteins were determined by immunoblotting, whereas the levels of Gi alpha-2 and Gi alpha-3 and adenylyl cyclase type V enzyme mRNA were determined by Northern-blotting techniques.. The blood pressure was significantly increased in DOCA-salt-treated rats as compared to sham-operated rats after 2 to 4 weeks of treatment; whereas no change in blood pressure was observed after 1 week of treatment (prehypertensive state). However, the levels of Gi alpha-2, Gi alpha-3 and G beta proteins and Gi alpha-2 and Gi alpha-3 mRNA were significantly enhanced in hearts and aorta from DOCA-salt treated rats after 1 week of treatment and remained elevated up to 4 weeks of treatment. In addition, the Gi-mediated inhibitions of adenylyl cyclase by Angiotensin II (Ang II) and C-ANF4-23 were also greater in DOCA-salt-treated rats as compared to sham-operated rats after 1 week and longer periods of treatments (2 to 4 weeks). On the other hand, the levels of Gs alpha were not altered up to 2 weeks of DOCA-salt treatment but significantly decreased in rats treated for 3 and 4 weeks. Furthermore, the stimulatory effects of guanine 5'-[gamma-thio]triphosphate (GTP gamma S), isoproterenol and forskolin on adenylyl cyclase were decreased in both hearts and aorta from DOCA-salt-treated rats after 1 to 4 weeks of treatment as compared to sham-operated rats. The mRNA levels of adenylyl cyclase, type V enzyme in hearts from DOCA-salt treated rats were significantly decreased after 3 and 4 weeks of DOCA-salt treatment but not in rats treated for 1 or 2 weeks.. These results indicate that the enhanced expression of Gi alpha-2 and Gi alpha-3 precedes the development of blood pressure in DOCA-salt-induced hypertension. It can thus be suggested that the increased levels of Gi proteins and resulting decreased levels of cAMP may be one of the factors that contribute to the impaired cardiac contractility and increased vascular tone in DOCA-salt hypertension.

Topics: Adenylyl Cyclases; Adrenergic beta-Agonists; Angiotensin II; Animals; Aorta; Atrial Natriuretic Factor; Autoradiography; Blotting, Northern; Colforsin; Desoxycorticosterone; GTP-Binding Protein alpha Subunits, Gi-Go; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Hypertension; Immunoblotting; Isoproterenol; Peptide Fragments; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sarcolemma; Sodium Chloride; Time Factors

The sensitivity of the myofilaments to Ca2+ is increased during agonist-induced contraction of vascular smooth muscle. Given the important contribution of vascular tone to the elevation of peripheral resistance observed in genetic hypertension, we have investigated whether alterations in myofilament Ca2+ sensitivity occur in small arteries from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) controls during the developmental and established phases of hypertension. Segments of mesenteric, renal, and femoral artery with an average lumen diameter <300 microm from 5- or 20-week-old rats were mounted in a wire myograph. Morphological measurements were made and the vessels permeabilized with Staphylococcus aureus alpha-toxin. Dose-response curves to increasing concentrations of Ca2+ were obtained and the ability of 100 nmol/L endothelin-1 (ET-1) or 10 micromol/L norepinephrine (NE) in the presence of 10 micromol/L GTP to enhance tension in response to low Ca2+ (pCa6.7) was determined. Systolic, diastolic, and mean blood pressures were higher in SHR than in WKY at 5 and 20 weeks. The media thickness:lumen diameter ratio was increased in mesenteric and femoral arteries from SHR compared with WKY at 5 and 20 weeks. There was no difference in media thickness:lumen diameter ratio in renal arteries or between 5- and 20-week animals in any vascular bed. The pCa curves were not different in mesenteric, renal, or femoral arteries from hypertensive compared with normotensive rats or between age groups, except in femoral arteries at 20 weeks, which exhibited a greater sensitivity to Ca2+ in SHR. Tension developed in response to maximal Ca2+ (pCa5.0) was greater in permeabilized mesenteric arteries from SHR compared with WKY at 20 weeks of age only; media stress was again similar in both strains but increased in older animals compared with younger animals in mesenteric arteries from WKY. The submaximal contraction induced by pCa6.7 was greater in femoral and renal than mesenteric arteries. GTP (10 micromol/L) augmented the tension developed to pCa6.7 in mesenteric arteries at 5 and 20 weeks and in renal arteries at 20 weeks. Addition of 100 nmol/L ET-1 or 10 micromol/L NE in the continued presence of GTP markedly increased tension in mesenteric arteries at 5 and 20 weeks. In renal arteries, 10 micromol/L NE enhanced Ca2+ sensitivity in the presence of GTP in SHR at 5 and 20 weeks and WKY at 5 weeks. In femoral arteries, there was a tendency for ET-

Topics: Aging; Animals; Animals, Newborn; Arteries; Blood Pressure; Calcium; Drug Resistance; Endothelin-1; Femoral Artery; Guanosine Triphosphate; Hypertension; Male; Mesenteric Arteries; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Renal Artery; Vasoconstriction; Vasoconstrictor Agents

Functional defects in purinergic neurotransmission have been related to the development of arterial hypertension in spontaneously hypertensive rats. In order to elucidate the molecular basis of this perturbation, we have directly characterized adenosine A1 receptors using radioligand binding to rat brain membranes of Wistar Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Saturation studies with [3H]1,3-dipropylcyclopentylxanthine ([3H]DPCPX) showed a lower affinity in both 5- and 48-week-old SHRSP in comparison with age-matched WKY. Similarly, competition experiments with [3H]DPCPX showed lower affinity of R-N6-phenylisopropyladenosine for the low-affinity binding site in 5- and 48-week-old SHRSP in comparison with WKY. In both studies, the difference in KD values was abolished by guanosine-5'-triphosphate in 5-week-old rats and mitigated in 48-week-old animals. No differences in Bmax values were observed in 5-week-old rats, whereas in 48-week-old SHRSP the number of receptors was significantly higher in comparison with age-matched WKY. Saturation experiments with the A1-selective agonist [3H]2-chloro-N6-cyclopentyladenosine ([3H]CCPA) demonstrated a higher affinity in 5-week-old SHRSP, whereas in 48-week-old hypertensive animals it was lower than in control WKY rats. No difference in receptor number was detected in comparison with age-matched WKY. In conclusion, our data demonstrated a diminished affinity of central adenosine A1 receptors for antagonists and for the low affinity state of the agonist binding site in genetically hypertensive rats. This might be due to structural changes of the receptor protein, to an altered G protein or defective receptor-G protein coupling in arterial hypertension.

Topics: Adenosine; Animals; Binding, Competitive; Brain; Female; GTP-Binding Proteins; Guanosine Triphosphate; Hypertension; Radioligand Assay; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Purinergic; Xanthines

It has been demonstrated that the adenylate cyclase activity of vascular smooth muscle regulates its tonus. The present study was undertaken to examine adenylate cyclase activity in early and established deoxycorticosterone acetate (DOCA)/salt hypertensive rats. Early and established DOCA/salt hypertensive rats were prepared by injecting 30 mg of DOCA weekly for 3 and 10 weeks, respectively, into male Wistar rats given drinking water with 1% saline. The membrane protein fraction medium containing the protein, 50 microM isoproterenol, 100 microM GTP, 50 microM forskolin or 25 microM calmodulin was applied. The adenylate cyclase activity was determined by a modified method developed in our laboratory using double isotope counting. The adenylate cyclase activity in the early DOCA/salt hypertensive rats was significantly higher (p less than 0.05) than that in the control rats in the basal condition, which was unaffected by additions of isoproterenol, GTP or forskolin. There was no significant difference in basal adenylate cyclase activity between the established DOCA/salt hypertensive and control rats. The adenylate cyclase activities in the established DOCA/salt hypertensive rats were significantly lower with GTP (p less than 0.02) and forskolin (p less than 0.01) as compared with the control rats. Calmodulin elevated the adenylate cyclase activity significantly (p less than 0.05) in the established DOCA/salt hypertensive rats as well as in the control rats. However, enzyme activity with calmodulin in the established DOCA/salt hypertensive rats was significantly lower (p less than 0.05) than that in the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenylyl Cyclases; Animals; Aorta, Thoracic; Calmodulin; Colforsin; Desoxycorticosterone; Guanosine Triphosphate; Hypertension; In Vitro Techniques; Isoproterenol; Male; Muscle, Smooth, Vascular; Rats; Rats, Inbred Strains; Saline Solution, Hypertonic

Isolated ventricular myocytes from adult (16 to 20 weeks) spontaneously hypertensive (SHR) and normotensive (WKY) rats were utilized to examine adrenergic and cholinergic receptor expression and interaction. Binding assays were performed using quinuclidinyl benzilate (QNB) and iodocyanopindolol (ICYP) for cholinergic and beta-adrenergic receptors, respectively. In addition, cAMP was measured as an index of adrenergic-cholinergic control of adenylate cyclase. Data from radioligand binding experiments indicated that muscarinic cholinergic receptors were depressed (22%) in SHR myocytes, while beta-adrenergic receptor density was comparable to that of WKY myocytes. Heterologous receptor modulation in isolated myocytes as assessed by displacement analysis with and without guanosine 5'-triphosphate (GTP), showed that carbachol displacement of QNB was shifted five fold to the right in the presence of GTP and that the beta-adrenergic agonist isoproterenol did not prevent the GTP-mediated binding alteration. In contrast, carbachol modulated the GTP-shift of ICYP displacement by isoproterenol and these effects were comparable in both WKY and SHR myocytes. Furthermore, the ability of carbachol to blunt the stimulation of adenylate cyclase by isoproterenol was also comparable in myocytes isolated from adult SHR and control animals. Thus, the observed decrement in muscarinic cholinergic receptor expression did not alter adrenergic-cholinergic interactions as assessed by displacement assays using guanine nucleotides, or the control of cAMP levels. In addition, isolated myocytes provide a useful system for analyzing receptor expression and regulation and how these parameters may be altered in the hypertensive heart.

Topics: Adenylyl Cyclases; Animals; Blood Pressure; Carbachol; Guanosine Triphosphate; Hypertension; In Vitro Techniques; Iodocyanopindolol; Isoproterenol; Kinetics; Male; Myocardium; Pindolol; Quinuclidinyl Benzilate; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, beta; Receptors, Cholinergic

1. Arterial relaxant responses to beta-adrenoceptor agonists are decreased in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar-Kyoto rats (WKY). To establish which component of the beta-adrenoceptor.adenylate cyclase (AC) system is impaired in the SHR arteries, effects of two activators of AC--cholera toxin (CTX) and forskolin--and of dibutyryl cyclic AMP (db cyclic AMP) were compared between strips of femoral arteries isolated from 13 week-old SHR and age-matched WKY. 2. In the absence of timolol, a beta-adrenoceptor antagonist, contractile responses of the strips to noradrenaline (NA) were significantly greater in the SHR than in the WKY. Timolol augmented the contractile responses to NA to a smaller extent in the SHR than in the WKY. 3. After blockade by timolol of beta-adrenoceptors, contractile responses of the strips to NA through the activation of alpha-adrenoceptors were not significantly different between the two strains. 4. Pre-treatment of the strips with CTX, an activator of the stimulatory GTP-binding protein (Gs), produced a slow-onset and long-lived antagonism of the alpha-adrenoceptor-mediated contractions. The antagonism was much smaller in the SHR than in the WKY. 5. The dose-response curves of the strips from both strains for alpha-adrenoceptor stimulation with NA determined after pretreatment with CTX were comparable to those determined in the absence of timolol. 6. Forskolin, an activator of the catalytic subunit of AC, and DB cyclic AMP also antagonized the alpha-adrenoceptor-mediated contractions. However, these antagonisms were not significantly different between the two strains. 7. Isobutyl methylxanthine (IBMX), an inhibitor of cyclic AMP phosphodiesterase, produced a similar antagonism of the alpha-adrenoceptor-mediated contractions between the two strains. 8. These results suggest that a reduced function of Gs is the main factor responsible for the decreased responsiveness to beta-adrenoceptor stimulation in the SHR femoral artery.

Topics: 1-Methyl-3-isobutylxanthine; Adrenergic alpha-Antagonists; Animals; Bucladesine; Cholera Toxin; Colforsin; Femoral Artery; GTP-Binding Proteins; Guanosine Triphosphate; Hypertension; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth, Vascular; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, beta; Timolol

The beta-adrenergic receptor-adenylate cyclase system of the cardiac membranes in spontaneously hypertensive rats (SHR) 14 weeks old was studied. The maximal activity of the catalytic unit of adenylate cyclase stimulated by purified stimulatory guanine nucleotide-binding protein (Ns) or forskolin was higher in SHR than in control Wistar-Kyoto (WKY) rats. However, adenylate cyclase activity stimulated by isoproterenol and GTP was the same between SHR and WKY rats. Although there was no difference in the amount of Ns which was measured by cholera toxin-catalyzed ADP-ribosylation, the functional activity of Ns in cholate-extracted membranes from SHR was significantly lower than that from WKY rats. There were no strain differences in the number and affinity of beta-adrenergic receptors; the function and amount of the inhibitory guanine nucleotide-binding protein (Ni), and the amount of beta gamma-subunits of Ns and Ni. These findings showed that there is an abnormal signal transduction in this system in SHR due to a reduction in the functional activity of alpha-subunits of Ns.

Topics: Adenylyl Cyclases; Animals; Cholera Toxin; Colforsin; Enzyme Activation; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Hypertension; Isoproterenol; Myocardium; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY; Receptors, Adrenergic, beta; Sarcolemma; Thionucleotides

Baclofen-sensitive GABAB receptor binding to various brain regions was compared in age-matched spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rat. The specific [3H]baclofen binding was significantly higher in SHR cerebellum, hippocampus and nucleus tractus solitarii (NTS), but lower in medulla, when compared with WKY. Scatchard analysis of the binding isotherms indicated a higher Bmax of the high affinity sites in SHR cerebellum and hippocampus and a lower Bmax of the same sites in SHR medulla. Guanyl nucleotide (GTP) decreased [3H]baclofen binding in brain regions of SHR and WKY, although the percentage inhibition of binding did not differ between SHR and WKY. The basal adenylate cyclase activity in SHR cerebellum was lower, in contrast to higher [3H]baclofen binding, whereas lower baclofen binding in SHR medulla was accompanied with higher adenylate cyclase activity. (+/-)Baclofen inhibited adenylate cyclase activity in both SHR and WKY rat brain. Among various regions, the percentage inhibition of cyclase activity in SHR cerebellum was significant lower, as compared to WKY cerebellum. These results suggest that activity of GABABergic mechanisms may be different in SHR and WKY rat brain.

Topics: Adenylyl Cyclases; Animals; Baclofen; Brain; Cerebellum; Guanosine Triphosphate; Hippocampus; Hypertension; Male; Medulla Oblongata; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, GABA-A

Studies on the rats with genetically-controlled hypertension (spontaneously hypertensive rats, SHR) in which myocardiopathy had been produced by isoproterenol (ISP) administration (2 X 80 mg/kg sc daily for two days) have shown that the myocardiopathy results in a fall of the activity of adenylate cyclase (AC) lasting from the second to the fourth day after administration of ISP, while the activity of phosphodiesterase (PDE) remained unchanged. In vitro, ISP (10(-7)-10(-4)M), Mg2+ (4-25nM), GTP (10(-6)-10(-5)M) and GTP (10(-5)M) given in combination with ISP (10(-6)-10(-5)M) elevated the AC activity in the cardiac muscle of SHR similarly in controls and the rats with ISP-induced myocardiopathy. The results indicate that the depression of AC activity in the cardiac muscle of SHR following ISP-induced myocardiopathy is a result of reduction of the number of AC molecules rather than a consequence of the structural damage of AC.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenylyl Cyclases; Animals; Cardiomyopathies; Cell Membrane; Cyclic AMP; Guanosine Triphosphate; Hypertension; Isoproterenol; Male; Myocardium; Rats

The stimulation of adenylate cyclase activity by guanine nucleotides, isoproterenol and fluoride has been investigated in KCl washed rat aortic membranes. We observed that the presence of guanine nucleotides in the assay was obligatory for the isoproterenol stimulation of adenylate cyclase activity. Guanine nucleotides could stimulate adenylate cyclase in the absence of catecholamines; however, the extent of stimulation was significantly lower (p less than 0.05) than that observed with isoproterenol. The order of effectiveness of guanine nucleotides was guanosine 5'-0-(3-thiotriphosphate) (GTP-gamma-S), 5'-guanylylimido diphosphate (Gpp(NH)p), and guanosine 5'-triphosphate (GTP). GTP stimulated enzyme activity without a noticeable lag period, while stimulation by Gpp(NH)p showed a lag period of 3-4 min. Addition of isoproterenol neither abolished the lag period, nor altered the apparent K1 value (concentration required for half maximal stimulation) for Gpp(NH)p stimulation. In a comparative study of adenylate cyclase activity between spontaneously hypertensive rats (SHR) and Kyoto Wistar normotensive rats (WKY), using 0.6 M KCl washed membranes from aorta and caudal artery, no differences were observed in the basal adenylate cyclase activity. However, guanine nucleotide-, isoproterenol-, and fluoride-stimulated enzyme activity was significantly lower (P less than 0.05) in the caudal artery of SHR as compared to WKY.

Topics: Adenylyl Cyclases; Animals; Aorta; Dose-Response Relationship, Drug; Guanosine Triphosphate; Hypertension; Isoproterenol; Muscle, Smooth, Vascular; Propranolol; Rats; Rats, Inbred Strains; Sacrococcygeal Region