The long range objectives of this project are to determine the exact metabolic site or sites of action of important cardioactive drugs, ions and hormones in myocardial tissue. The relationships between these cardioactive substances, myocardial contractility and levels of important metabolic intermediates will be correlated. Substances such as digitalis, beta adrenergic agents, glucagon, calcium ion, lidocaine, beta adrenergic blocking agents, phosphodiesterase inhibitors and insulin will be studied. Initially the relationship between these agents and hormone second messengers cyclic AMP and cyclic GMP will be determined in perfused frog ventricles and isolated rabbit atria. In addition, studies will be conducted to determine the turnover rate and whether specific pools of these cyclic nucleotides exist within the myocardial cell. In addition, some efforts on the development of new methodology to achieve these research goals have yielded exciting new methodology. A high pressure chromatographic system with specific phosphate and U.V. detection allows for analysis of nucleotide and sugar phosphate intermediates of metabolism. New radioimmunoassays for cyclic AMP and cyclic GMP using acetylation of samples have facilitated the assay of cyclic AMP and cyclic GMP at levels as low as 1 femtomole. Finally, a completely automated analytical system for radioimmunoassays has been developed and can assay many drugs and hormones at rates of 35 samples per hour. BIBLIOGRAPHIC REFERENCES: Terasaki, W.T. and Brooker, G: Cardiac Adenosine 3':5'-Monophosphate: Free and Bound Forms in the Intact Rat Atrium. Journal of Biological Chemistry 252, 1041, 1977. Hsu, C.Y. and Brooker, G.: Characteristics of Serum Inhibition of Epinephrine Stimulated Cyclic AMP Accumulation in a Rat Glioma Cell Line (C6-2B). Federation Proceedings, Spring 1977.