guanylyl-imidodiphosphate and Cardiomyopathies

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

In order to explain the attenuated sympathetic support during the development of heart failure, the status of beta-adrenergic mechanisms in the failing myocardium was assessed by employing cardiomyopathic hamsters (155-170 days old) at moderate degree of congestive heart failure. The norepinephrine turnover rate was increased but the norepinephrine content was decreased in cardiomyopathic hearts. The number and the affinity of beta receptors in the sarcolemmal preparations were not changed in these hearts at moderate stage of congestive heart failure. While the basal adenylyl cyclase activity was not altered in sarcolemma, the stimulation of enzyme activity by NaF, forskolin, Gpp(NH)p or epinephrine was depressed in hearts from these cardiomyopathic hamsters. Since G-proteins are involved in modifying the adenylyl cyclase activity, the functional and bioactivities as well as contents of both Gs and Gi proteins were determined in the cardiomyopathic heart sarcolemma. The functional stimulation of adenylyl cyclase by cholera toxin, which activates Gs proteins, was markedly depressed whereas that by Pertussis toxin, which inhibits Gi proteins, was markedly augmented in cardiomyopathic hearts. The cholera toxin and pertussis toxin catalyzed ADP-ribosylation was increased by 37 and 126%, respectively; this indicated increased bioactivities of both Gs and Gi proteins in experimental preparations. The immunoblot analysis suggested 74 and 124% increase in Gs and Gi contents in failing hearts, respectively. These results suggest that depressed adenylyl cyclase activation in cardiomyopathic hamsters may not only be due to increased content and bioactivity of Gi proteins but the functional uncoupling of Gs proteins from the adenylyl cyclase enzyme may also be involved at this stage of heart failure.

Topics: Adenosine Diphosphate Ribose; Adenylate Cyclase Toxin; Adenylyl Cyclases; Animals; Cardiomyopathies; Cholera Toxin; Colforsin; Cricetinae; Dihydroalprenolol; Epinephrine; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Heart; Heart Failure; Myocardium; NAD; Norepinephrine; Pertussis Toxin; Sarcolemma; Sodium Fluoride; Virulence Factors, Bordetella

The aim was to study the activity of receptors coupled to guanine nucleotide binding regulatory proteins (G proteins) in doxorubicin induced cardiomyopathy, with special attention to G proteins, beta adrenoceptors, muscarinic receptors, and adenylyl cyclase.. Messenger RNA of G proteins, densities and high affinity agonist binding of beta adrenoceptors and muscarinic receptors, activity of adenylyl cyclase, calcium influx, and in vivo lipid peroxidation were determined before, in the early stage, and in the later stage of doxorubicin cardiomyopathic heart failure.. Sprague-Dawley rats between 150-200 g were used. Doxorubicin was given intravenously at two doses of 4 mg.kg-1 and 6 mg.kg-1 every third week (1st, 4th, 7th week) for nine weeks. Doxorubicin treated rats plus corresponding controls were killed at 3 weeks (n = 7), 6 weeks (n = 7), and 9 weeks (n = 6), respectively.. Northern blot and dot blot hybridisations of the total RNA revealed that messenger RNA of both stimulatory and inhibitory G proteins were identical between doxorubicin treated rats and controls. No alterations in the densities of beta adrenoceptors and muscarinic receptors were observed, neither did the high affinity agonist binding of beta adrenoceptors and muscarinic receptors change. Furthermore, modulation of adenylyl cyclase was unimpaired. In contrast, Ca(2+)-ATPase and serum water soluble fluorescent substance, a product of in vivo lipid peroxidation, were shown to increase dramatically in doxorubicin treated rats (4 mg.kg-1 for 6 and 9 weeks, 6 mg.kg-1 for 3, 6 and 9 weeks) as compared with corresponding controls.. The findings suggest that, despite increased calcium influx and lipid peroxidation in doxorubicin induced cardiomyopathy, the activity of receptors coupled to G proteins remained normal.

Topics: Adenylyl Cyclases; Animals; Calcium; Cardiomyopathies; Doxorubicin; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Male; Rats; Rats, Inbred Strains; Receptors, Adrenergic, beta; Receptors, Muscarinic

Recent reports suggested that a complex alteration in beta-receptor function occurs in failing human myocardium. We evaluated beta-receptor-subtype activity in an experimental model of monocrotaline (MCT)-induced cardiomyopathy in the rat. Through pulmonary hypertension, MCT causes right ventricular hypertrophy (RVH), either associated with heart failure or not, beta-Receptor function was evaluated in both failing-hypertrophic and hypertrophic hearts in binding studies with [125I]iodocyanopindolol (ICYP) and by measuring adenylate cyclase (AC) activity. In the right failing ventricle, beta 1- but not beta 2-receptor density was decreased. Lesion-associated modifications in the adenylate cyclase system were also observed: isoproterenol- and guanosine 5' [beta, gamma-imido]triphosphate [Gpp(NH)p]-stimulated cyclic AMP formation was reduced in the right failing ventricle, while the cyclic AMP responses to NaF and forskolin were unchanged. On the other hand, no changes in either beta-receptor density or function were found in hypertrophic ventricles. MCT-induced heart failure in the rat is thus associated with a selective decrease of beta 1-receptor density and function. These results suggest that MCT-induced cardiac failure may be an appropriate model in which to investigate heart insufficiency further.

Topics: Adenylyl Cyclases; Animals; Autoradiography; Cardiac Output, Low; Cardiomegaly; Cardiomyopathies; Female; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Iodocyanopindolol; Monocrotaline; Pindolol; Pyrrolizidine Alkaloids; Rats; Rats, Inbred Strains; Receptors, Adrenergic, beta

The effect of chronic experimental diabetes on the adenylate cyclase system (AC) in the rat heart was investigated. Rats were made diabetic by an intravenous injection of streptozotocin (65 mg/kg), hearts were removed 8 weeks later and washed cell particles were isolated. AC activity was measured in the absence and presence of different concentrations of forskolin, NaF, GTP analogue [Gpp(NH)p] or epinephrine. A significant depression in the epinephrine stimulated AC activity was observed in diabetic hearts. Basal AC activity and stimulation of AC with forskolin, NaF and Gpp(NH)p were not significantly different between control and diabetic preparations. These results indicate no apparent alterations in the regulatory or catalytic properties of AC in hearts from chronic diabetic rats. The observed depression in epinephrine stimulated AC activity may account for the depressed inotropic action of catecholamines in the diabetic cardiomyopathy.

Topics: Adenylyl Cyclases; Animals; Cardiomyopathies; Diabetes Mellitus, Experimental; Epinephrine; Guanylyl Imidodiphosphate; Heart Ventricles; Kinetics; Male; Myocardium; Rats; Rats, Inbred Strains