TSH and ACTH Secretion and Cyclic Adenosine 3'5' Monophosphate Content following Stimulation with TRH or Lysine Vasopressin in Vitro: Suppression by Thyroxine and Dexamethasone

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Abstract
The studies reported here demonstrate temporally related changes in rat pituitary hormone release and levels of c[cyclic]AMP following stimulation with either TRH [thyrotropin releasing hormone] or LVP [lysine vasopressin]. They thus strengthen the postulation that cAMP is a 2nd messenger in the action of releasing hormones on the pituitary. A divergence between hormone release and pituitary cAMP levels was noted in several instances. Therefore, a definitive role for cAMP as mediator of anterior pituitary hormone release was not established. Target gland hormone feedback in vitro can inhibit releasing factor produced elevations of pituitary cAMP levels and suggest such an action may be a method by which target gland hormones inhibit tropic hormone release.