EFFECT OF GLUCAGON ON RAT HEART ADENYL CYCLASE

Washed particulate preparations of adenyl cyclase from rat heart were used to catalyze the formation of cyclic 3′,5′-AMP from ATP in the presence of Mg++ and caffeine. Similar preparations from other tissues have been previously used to study the effects of a variety of hormones on adenyl cyclase. In the present study, the effect of glucagon on heart adenyl cyclase was compared to that of epinephrine in the same experiments. Glucagon was about 1.5 times more effective than l-epinephrine on a molar basis in stimulating cyclic 3′,5′-AMP formation. The effects of glucagon and epinephrine were not additive indicating a single adenyl cyclase activity in the preparations. The effect of l-epinephrine but not of glucagon could be blocked by beta-adrenergic blocking agents. These observations indicated that these hormones increased heart adenyl cyclase activity by different mechanisms. Cyclic 3′,5′-nucleotide phosphodiesterase was effectively blocked with caffeine in the incubation mixtures. In the absence of caffeine, moderate amounts of added cyclic 3′,5′-AMP were hydrolyzed by this enzyme, but this was similar in the absence and presence of glucagon. © 1969.