Inhibition by somatostatin of the vasopressin-stimulated adenylate cyclase in a kidney-derived line of cells grown in defined medium

AbstractLLC-PK1L cells, a kidney-derived cell line grown in defined medium, possess a vasopressin-sensitive adenylate cyclase. Somatostatin was able to inhibit the vasopressin-induced increase in adenylate cyclase activity, without affecting the basal enzyme activity. This inhibition was competitive. No effect of somatostatin could be detected on [3H]vasopressin binding suggesting an interaction of somatostatin with the vasopressin-sensitive system distal to the hormone—receptor interaction. At variance with N6-L-2-phenylisopropyladenosine (PIA), GTP did not potentiate the inhibition by somatostatin. The inhibition of the vasopressin stimulation by somatostatin and that by PIA were additive. Changing the composition of the cell growth medium increased the number of vasopressin receptors per cell. Cells with a high number of vasopressin receptors were less sensitive to inhibition by somatostatin. Such results suggested that somatostatin and vasopressin receptors and/or the inhibitory (Ni) and stimulatory (Ns) regulatory transducing components are regulated by different mechanisms