Stress-related effects on the secretion of progesterone by the adrenals in castrated male rats presented to stimulus males. Involvement of oestrogen.

Abstract

Rats were orchidectomized (ORCH) as adults and given successive doses of 0.5 microgram or 1.0 microgram of oestradiol benzoate (EB) combined or not with dexamethasone (DEXA) at the end of oestrogen treatment; successive doses of olive oil. They were presented to stimulus males on the day of the last EB injection and decapitated immediately after the behavioural test. Animals given EB or olive oil only served as controls. There was a significant rise in blood progesterone concentration in animals given 0.5 and 1.0 microgram EB as compared with oil-treated animals. A higher blood progesterone concentration was observed at the end of the behavioural session in oil-treated and 0.5 microgram EB-treated ORCH rats than in their isolated counterparts, an effect which appeared not to dependent on lordosis responses to mounting attempts of the males. DEXA completely suppressed the rise in blood progesterone concentration in oestrogenized ORCH rats presented to stimulus males. Presentation of ORCH rats to stimulus males was then concluded to constitute a stressful condition capable of inducing adrenocortical progesterone secretion in ORCH animals.