Effect of stress on tissue and plasma levels of immunoreactive beta-endorphin in ovariectomized rats primed with oestrogen and progesterone

Abstract

The aim of this study was to investigate the effect of oestrogen and progesterone on levels of immunoreactive beta-endorphin (Ir-beta-EP) in the hypothalamus, anterior pituitary gland, neurointermediate lobe and plasma under normal conditions and conditions of stress. The injection of oestrogen + progesterone into ovariectomized rats increased Ir-beta-EP levels in extracts of anterior pituitary tissue and in plasma, under both normal and stressed conditions. Exposure to a stress reduced the content of anterior pituitary Ir-beta-EP in ovariectomized rats treated with oestrogen + progesterone and also with sesame oil. Such treatment only resulted in increments in plasma Ir-beta-Ep in oil-treated but not in oestrogen + progesterone-treated ovariectomized rats. It was concluded (1) that oestrogen and progesterone are involved in the regulation of resting levels of anterior pituitary Ir-beta-EP during the rat oestrous cycle, (2) that stress reduces levels of anterior pituitary Ir-beta-EP and (3) that increased levels of plasma oestrogen + progesterone inhibit plasma Ir-beta-EP increments which normally accompany exposure to stress.