Abstract
Corticotropin releasing hormone (CRH) stimulation of ACTH release and cyclic AMP-mediated events involved in the control of ACTH release were compared in sham-operated and adrenalectomized rats. CRH-stimulated adenylate cyclase activity was decreased in pituitary homogenates from adrenalectomized animals. CRH-stimulated cyclic AMP accumulation was essentially abolished and CRH-stimulated cyclic AMP-dependent protein kinase (A-kinase) activity was decreased in freshly prepared anterior pituitary cells from adrenalectomized animals. Basal and CRH-stimulated ACTH release was elevated in these cells. Since ACTH release is increased in adrenalectomized rats despite the down regulation of CRH-linked pituitary mechanisms, we speculate that the site of action of disinhibition by corticosterone of ACTH release (or synthesis) following adrenalectomy is distal to the generation of cyclic AMP and/or that non-CRH mediated mechanisms assume a greater role in ACTH regulation following adrenalectomy.
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