The Activity of Adenylate Cyclase, Phosphodiesterase and Protein Kinase in the Adenohypophyses of Rats Treated by Chronic Administration of Estrogens and Acute Application of Thyroxine In Vivo

Abstract

The activity of adenylate cyclase, phosphodiesterase and protein kinase was estimated in the adenohypophysis of rats treated by the chronic administration of estradiol (1 mg s.c per rat twice a week for 4-5 weeks) and acute application of 1-thyroxine (1 mg s.c. per rat 1-2 hours before sacrifice).

Estrogen treatment produced about 4-fold increase in the weight of adenohypophysis. Basal activity of adenylate cyclase and fluoride stimulated activity was unchanged while the stimulation by PGE₁ was strongly reduced. This effect was accompanied by a decrease in the activity of phosphodiesterase and protein kinase. Single administration of thyroxine also decreased the activity of adenylate cyclase, phosphodiesterase and protein kinase.

The possible consequences of these changes in specific activity, as well as in total amount of enzymes present in enlarged adenohypophyses after estrogen treatment are discussed and the usefulness to correlate the hormone release to cyclic AMP level in this gland under various hormonal states is suggested as one possibility for searching for the molecular mechanisms of hormone action in adenohypophysis.

Key words

Adenohypophysis - Cyclic AMP - Adenlylate cyclase - Phosphodiesterase - Protein kinase - Estrogen - Thyroxine - Prostaglandin E₁