Cyclic nucleotides in the cellular action of neurohypophyseal hormones

Cyclic 3',5'-nucleotides play an important role in the action of neurohypophyseal hormones on peripheral tissues. All available evidence indicates that cyclic AMP serves as an intracellular mediator in the regulatory action of neurohypophyseal hormones on transport of fluids and solutes across both mammalian and nonmammalian epithelial membranes. There is a close association among binding of neurohypophyseal hormones on membrane, stimulation of cyclic AMP generation, and the functional response. On the other hand, neurohypophyseal hormones have no similar effect on cyclic AMP metabolism in contractile tissues such as smooth muscle. It appears likely that neurohypophyseal hormones stimulate primarily generation of cyclic GMP in contractile tissues, and the increase in cyclic GMP levels may be associated with the contractile response. While the role of cyclic AMP in neurohypophyseal hormone effects in epithelia is firmly established, the possible role of cyclic GMP in contractile responses is largely hypothetical at the present time.