The role of cyclic nucleotides in effects of vasoactive agents on vascular tissue will be explored. Levels of cyclic AMP and cyclic GMP will be determined in artery strips in states of contraction and relaxation induced by catecholamines, ionic variations, histamine, acetyl choline and other vasoactive substances. Possible effects of these substances on adenyl and guanyl cyclase activities and on cyclic nucleotide phosphodiesterase activity in cell free systems will be investigated. Comparative studies will be carried out on vascular segments that vary in responsiveness to beta adrenergic agents in an attempt to define whether the variation occurs at the level of the interaction of the beta agent and adenyl cyclase or at a site distal to cyclic AMP formation.