Adrenocortical involution in rats during oestrus synchronisation with medroxyprogesterone

Abstract

Daily treatment of female rats with medroxyprogesterone acetate in aqueous suspension resulted in adrenocortical atrophy. The doses given were those used for oestrus synchronisation. Intramuscular injections of 2-0 mg medroxyprogesterone acetate were used to investigate the atrophic process. Adrenocortical involution was associated with extensive single cell deletion (apoptosis). It is suggested that theses changes were due to suppression of pituitary ACTH secretion. The cytological changes support the concept that single cell death plays an important role in organ remodelling. Biochemical determinations of DNA, RNA, protein and dry matter, and histological examination, did not reveal significant changes in the liver.

PIP: Clinical studies were carried out with laboratory female rats to ascertain the effects of daily dosing with MPA (medroxyprogesterone acetate). Some of the rats received .8 mg MPA in 1.4 ml acqueous suspension. The others received 2 mg MPA in intramuscular injections. The doses used were those necessary for estrus synchronisation. Body weight was increased by MPA given by gastric intubation. Liver weight, dry matter, protein, DNA, and RNA were not significantly affected by daily MPA, either by intubation or by injection. Adrenocortical atrophy occurred as a result of the MPA administration. This response was dose-dependent. Histologically, the loss of adrenal weight was due almost entirely to the involution of cortical cells. The mechanism of adrenocortical atrophy involved extensive single cell deletion, due perhaps to the suppression of pituitary ACTH secretion. No changes in the liver were observed through biochemical determinations.