The effect of cyclic adenosine- and guanosine 3′,5′-monophosphate on the normal and drug-increased coronary blood flow

Cyclic 3′,5′-AMP (cAMP), cyclic 3′,5′-GMP (cGMP) and their more lipo-phylic derivatives (cDBA, cMBA, cDBG) were studied in conscious, resting dogs prepared with chronically implanted electromagnetic flow probes and catheters. Coronary blood flow (CBF), heart rate, aortic blood pressure and in some cases, cardiac output were recorded. cAMP, cDBA and cMBA increased the normal and pharma-cologically elevated CBF while cGMP and its dibutyryl derivative were without effect. Pretreatment with theophylline, a phosphodiesterase inhibitor, diminished the effect of cAMP but enhanced the effect of cDBA and cMBA. The data suggest that cAMP cannot be considered as a second messenger responsible for the maintenance of coronary vascular tone. It may, however, be responsible for coronary vasodilation.