The effects of immobilization stress on beta-endorphin levels are modulated by testosterone

Abstract

Immunoreactive beta-endorphin (IR-BE) levels were determined in the anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL) and the hypothalamus of castrated male rats and castrated male rats treated with testosterone proprionate (TP), subsequent to exposure to acute (once for 45 min) or chronic (45 min each day for 15 consecutive days) immobilization stress. Acute stress resulted in a reduction in the concentration of IR-BE in the AP of castrated male rats, which was potentiated by TP. The concentration of IR-BE in the NIL was elevated by acute stress in castrated male rats and was not affected by acute stress in castrated male rats administered TP. Exposure to chronic immobilization stress elevated the concentration of IR-BE in the AP of castrated animals and not animals treated with TP. The concentration of IR-BE in the NIL of castrated animals was not altered by chronic immobilization. Chronic stress did result in a significant rise in the level of IR-BE in the NIL of castrated male rats given TP. Hypothlamic IR-BE levels in castrated male rats were reduced by TP and were not influenced by acute or chronic stress. Chromatographic analysis indicated that acute and chronic stress promoted the accumulation of beta-lipotropin rather than beta-endorphin in the AP. This effect was attenuated by TP. Beta-endorphin was the only form of immunoreactivity detected in the NIL and hypothalamus. These findings indicate that immobilization stress affects IR-BE levels in the AP and the NIL, and that the effects of acute and chronic immobilization stress of IR-BE levels in the AP and the NIL are modulated by testosterone.