Effect of thyroxine and of thyrotropin releasing hormone on cyclic AMP concentration in the anterior pituitary gland in vitro.

The effect TRH and thyroxine (T4) in vitro on the content of cAMP in the anterior pituitary gland in rat have been investigated. Thyroxine did not significantly affect this concentration, but TRH produced approximately a two-fold increase in the pituitary cAMP content. Preincubation of the anterior pituitary together with T4--under the conditions when the latter inhibited both proliferative and secretory response of the gland to TRH--did not prevent the elevation of cAMP due to TRH. It is assumed that T4 must have exerted its inhibitory effect outside of the cyclic AMP system.