Interactions of bovine thyrotropin and human chorionic gonadotropin with adenylate cyclase in bovine thyroid membranes.

Previous studies have shown that crude preparations of human chorionic gonadotropin bind to bovine thyroid membranes, displace 125I-labeled bovine thyrotropin therefrom, and are weak agonists therein with respect to the activation of adenylate cyclase. The present studies reveal that concentrations of chorionic gonadotropin sufficient to elicit a maximal agonistic response of adenylate cyclase are strongly antagonistic to the stimulatory action of bovine thyrotropin in the thyroid membrane system. This effect is reminiscent of the inhibitory effects of crude human chorionic gonadotropin on other extragonadal tissues in vitro, and, like them, appears to be mediated by some factor(s) other than human chorionic gonadotropin itself, since highly purified human chorionic gonadotropin was without effect.