6-ketoprostaglandin-f1-alpha and cilostamide

Infusion of forskolin, an adenylate cyclase activator, in concentrations (2 microM) that do not alter basal prostaglandin (PG) synthesis inhibit synthesis of PG elicited by isoproterenol in rabbit heart. This inhibitory action of forskolin appears to be dependent on cyclic AMP (cAMP). Bolus injection of forskolin (75 nmol), however, was found to stimulate PG synthesis in rabbit heart. The purpose of this study was to elucidate the mechanism of the stimulatory action of forskolin on PG synthesis (prostaglandin I2 measured as 6-ketoprostaglandin F1 alpha [6-keto-PGF1 alpha]) in isolated perfused rabbit heart. Forskolin enhanced PG production in a dose-dependent manner. 1,9-Dideoxyforskolin, a forskolin analogue devoid of adenylate cyclase-stimulating activity, also enhanced PG synthesis. The cAMP analogue chlorophenylthio-cAMP failed to stimulate output of 6-keto-PGF1 alpha, although this agent produced dose-related changes in mechanical function in rabbit heart. Furthermore, the adenylate cyclase inhibitor (-)-N6-(R-phenylisopropyl)adenosine potentiated, whereas the phosphodiesterase inhibitor cilostamide attenuated, forskolin-stimulated PG production. (-)-N6-(R-Phenylisopropyl)adenosine and cilostamide had no effect on the mechanical actions of chlorophenylthio-cAMP, suggesting selectivity of these agents for adenylate cyclase and phosphodiesterase, respectively. 6-Keto-PGF1 alpha output elicited by forskolin was abolished by reduction of calcium in the perfusion fluid as well as by the calcium channel blocker diltiazem. The intracellular calcium antagonists TMB-8 and ryanodine also abolished forskolin-stimulated PG synthesis in rabbit heart. PG synthesis stimulated by 1,9-dideoxyforskolin was also prevented by reduced extracellular calcium, diltiazem, and ryanodine. The calmodulin antagonists trifluoperazine, W-7, and calmidazolium failed to significantly alter PG production in response to forskolin. These results indicate that forskolin-stimulated PG synthesis in rabbit heart is independent of cAMP and requires calcium from both extracellular and intracellular sources.

Topics: 6-Ketoprostaglandin F1 alpha; Adenylyl Cyclases; Animals; Colforsin; Cyclic AMP; Diltiazem; Epoprostenol; Heart; In Vitro Techniques; Myocardium; Phenylisopropyladenosine; Phosphoric Diester Hydrolases; Prostaglandins; Quinolones; Rabbits; Stimulation, Chemical

beta-Adrenergic receptor activation in heart is associated with enhanced production of adenosine 3',5'-cyclic monophosphate (cAMP) and prostaglandins (PG). The purpose of the present study was to test the hypothesis that cAMP mediates or modulates PG synthesis elicited by activation of beta-adrenergic receptors in the isolated, perfused rabbit heart. Infusion of 8-(4-chlorophenylthio) (cpt)-cAMP (100 microM), an analogue of cAMP, or stimulation of endogenous cAMP generation with forskolin (2 microM) resulted in a reduction of perfusion pressure and an increase in heart rate and contractility but had no effect on 6-keto-PGF1 alpha output. 6-Keto-PGF1 alpha production elicited by a bolus injection of isoproterenol (Isop) (475 pmol), however, was reduced by greater than 50% in the presence of these agents, cpt-cAMP was also found to inhibit 6-keto-PGF1 alpha output elicited by the calcium ionophore A23187 but not that in response to exogenous arachidonic acid. Perfusion with the adenosine analogue adenylate cyclase inhibitor PIA (1 microM) enhanced by twofold Isop-stimulated output of 6-keto-PGF1 alpha, whereas cAMP accumulation was prevented. Isop-stimulated production of 6-keto-PGF1 alpha was inhibited by 50% in the presence of the phosphodiesterase inhibitors 1-methyl-3-isobutylxanthine (50 microM), Ro 20-1724 (300 microM), or cilostamide (5 microM), whereas both basal and Isop-stimulated cAMP accumulations were enhanced by these agents. These data suggest that cAMP acts as an inhibitory modulator of PG synthesis in response to beta-adrenergic receptor activation in rabbit heart.

Topics: 1-Methyl-3-isobutylxanthine; 3',5'-Cyclic-AMP Phosphodiesterases; 6-Ketoprostaglandin F1 alpha; Adenylyl Cyclase Inhibitors; Animals; Blood Pressure; Colforsin; Cyclic AMP; Epoprostenol; Heart; Heart Rate; In Vitro Techniques; Isoproterenol; Male; Myocardium; Phenylisopropyladenosine; Platelet Aggregation Inhibitors; Quinolones; Rabbits; Thionucleotides