EFFECTS OF THE PROLONGED GLUCAGON ADMINISTRATION ON THE RAT PITUITARY-ADRENOCORTICAL AXIS

The effects of a 6-day administration of glucagon (2.5 or 10 nmol/kg . day) on the rat adrenal cortex, and the acute action of glucagon (fro m 10(-10) to 10(-6) M) on dispersed adrenocortical cells were investig ated. The lower dose of glucagon induced hypertrophy of the adrenal co rtex, increased the blood levels of corticosterone and aldosterone, an d enhanced basal corticosterone (but not aldosterone) production by ad renal quarters. The plasma concentration of ACTH was not significantly affected. The higher dose of glucagon was almost completely ineffecti ve. Glucagon did not change basal aldosterone and corticosterone secre tion of dispersed adrenocortical cells. Taken together these findings suggest that the prolonged administration of the lower dose of glucago n enhances the growth and secretory activity of the rat adrenal cortex through indirect mechanisms not involving stimulation of the pituitar y ACTH release. Probably the higher dose of glucagon is able to evoke the release of an unknown anti-adrenocorticotropic factor overcoming t he stimulatory effect.