in an experimental canine model of low-output heart failure produced by chronic rapid ventricular pacing. The contractile response occurring after exposure to the P-adrenergic agonist dobutamine, measured as peak left ventricular +dP/dt, was decreased after 3 weeks of pacing. To further characterize the diminished functional responsiveness to 3-adrenergic receptor stimulation, ,3-adrenergic rec...

Despite their opposite effects on prolactin secretion, both dopamine and angiotensin II inhibit adenylate cyclase activity in homogenates of anterior pituitary cells in primary culture. Dopamine and angiotensin II inhibition of adenylate cyclase was not additive, suggesting that both neurohormones inhibit the adenylate cyclase of the lactotroph cells. Pretreatment with Bordetella pertussis toxi...

The murine Leydig tumor cell line, MLTC-1, has specific cell surface receptors for human chorionic gonadotropin (hCG), which are coupled to adenylate cyclase. When the cells were exposed to hCG, there was a loss of these receptors (down-regulation), which was both dose- and time-dependent. Down-regulation was inhibited by lowering the temperature, removing bound hormone or blocking protein synt...

In the presence of 1 microM atrial natriuretic factor (ANF) and low (0.1 mM) Mg2+ concentrations, the initial rate of binding of [3H]guanosine 5'-[beta, gamma-imido)triphosphate [( 3H]p[NH]ppG) to rat lung plasma membranes was increased twofold to threefold. ANF-dependent stimulation of the initial rate of [3H]p[NH]ppG binding was reduced at high (5 mM) Mg2+ concentrations. Preincubation of mem...

In adipocytes, adenylate cyclase is positively regulated by beta-adrenergic agents and negatively regulated by adenosine. Incubation of adipocytes with adenosine deaminase relieves the inhibition of adenylate cyclase by destroying the adenosine that the cells release into the medium. When adipocytes are incubated with adenosine deaminase and the beta-adrenergic agent isoproterenol, most of thei...

Pancreatic islets contain calmodulin. The protein binds to a particulate fraction derived from the islets and stimulates adenylate cyclase activity in this subcellular fraction, both phenomena being activated by ionized calcium. A calcium-dependent stimulation of adenylate cyclase by endogenous calmodulin may contribute to the accumulation of adenosine 3',5'-monophosphate evoked by insulin rele...

1. Incubation of human platelet membranes with guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) causes a time-dependent increase in the activation of adenylate cyclase due to Gs (the stimulatory GTP-binding protein). Forskolin enhances adenylate cyclase activity but does not interfere with the process of activation. The activation follows first-order kinetics in both the presence and the ...

A distinctive Mn-2+-sensitive adenylate cyclase [ATP pyrophosphate-lyase(cyclizing), EC 4.6.1.1] system insensitive to fluoride has been found in rat seminiferous tubules and epididymal sperm. The development of this distinctive adenylate cyclase in testis was studied during spermatogenesis. It was first detectable in seminiferous tubules in immature rats at about the time of the first reductiv...

In rat striatum, the activation of adenylate cyclase by the endogenous Ca2+-binding protein, calmodulin, is additive with that of GTP but is not additive with that of the nonhydrolyzable GTP analog, guanosine-5'-(beta, gamma-imido)triphosphate (GppNHp). One possible mechanism for this difference could be an effect of calmodulin on GTPase activity which has been demonstrated to "turn-off" adenyl...

A subcellular fraction prepared from rat kidney medulla contained vasopressin-sensitive adenylate cyclase and vasopressin binding sites. Vasopressin stimulation resulted in an increase in the maximal velocity of the reaction with no change in the apparent K, for ATP. A maximum activation ratio (5 to 10) was obtained at low Mg2+ concentration (0.75 mM) and pH 7.4. The apparent Km for vasopressin...