The effect of inotropic agents on glycerol release and protein kinase activity ratios in the isolated perfused rat heart.

Glycerol release was employed as an index of endogenous glyceride hydrolysis in rat hearts perfused by a Langendorff technique with Krebs-Henseleit-bicarbonate buffer containing 5.5 mM glucose. Changes in cardiac contractility induced by glucagon, isoproterenol, epinephrine and ouabain were associated with an increase in glycerol efflux from the heart in a dose-dependent fashion. Propranolol, a beta adrenergic blocking agent, markedly diminished the increase in glycerol release due to isoproterenol without affecting this same parameter subsequent to glucagon or ouabain infusion. Insulin, a potent antilipolytic agent in adipose tissue failed to diminish glycerol efflux elicited by any of the inotropic agents studied. Protein kinase activity ratios were employed as an index of cyclic adenosine 3':5'-monosphate levels. Increases in cardiac contractility and glycerol efflux induced by isoproterenol and glucagon were associated with increases in protein kinase activity ratios while increases in contractility and glycerol efflux induced by ouabain were not accompanied by an increase in protein kinase activity ratios.