Responses of isolated dog blood vessels to glucagon

The responses to glucagon were compared in helical strips of different arteries or veins isolated from dogs, and the relationship between the glucagon-induced relaxation and the intracellular cyclic AMP content in the arteries was studied. Relaxations induced by glucagon followed the order renal greater than mesenteric greater than femoral greater than cerebral = coronary arteries precontracted with PGF2 alpha. Glucagon-induced relaxations were greater in renal and mesenteric arteries than in the respective veins. Removal of the endothelium from the renal artery did not alter the magnitude of relaxations induced by glucagon nor the apparent ED50 value of glucagon. Glucagon increased the intracellular cyclic AMP content in both renal and coronary arteries, but the nucleotide increments were significantly greater in renal arteries than in coronary arteries. Isoproterenol produced significant increases in the intracellular cyclic AMP content and relaxations in renal and coronary arteries. Relaxations induced by dibutyryl cyclic AMP were greater in coronary arteries than in renal arteries. It is concluded that glucagon relaxed differently a variety of dog blood vessels, possibly by different extents of production of cellular cyclic AMP. The quantity and sensitivity of receptors for glucagon in smooth muscle cells may be heterogeneous in the vessels.