Role of phosphatidylinositol turnover in alpha 1 and of adenylate cyclase inhibition in alpha 2 effects of catecholamines

Abstract

Ligand binding and pharmacological studies have indicated that alpha-adrenergic receptors can be divided into alpha 1 and alpha 2. We suggest that alpha 1 receptors mediate those metabolic effects of alpha catecholamines which involve phosphatidylinositol turnover and the release of bound intracellular Ca 2+ as well as the entry of extracellular Ca 2+. In contrast, alpha effects of catecholamines are due to non-specific inhibition of adenylate cyclase through a mechanism independent of Ca 2+. A similar classification for the effects of both histamine and serotonin suggests that they have separate type 1 or alpha receptors for Ca 2+ dynamics which are different from type 2 or beta receptors which regulate adenylate cyclase. There is a significant correlation between hormone effects on phosphatidylinositol turnover and elevation of intracellular Ca 2+. The available data suggest that the turnover of membrane-bound phosphatidylinositol is involved in Ca 2+ gating in rat hepatocytes, rat and hamster adipocytes and blowfly salivary glands. In hamster adipocytes adenylate cyclase activity is also inhibited by alpha 2 catecholamines through a Ca 2+ independent mechanism.