Adrenocortical responses and changes during the oestrous cycle in mice: effects of male presence, male urine and housing conditions.

Male urine applied daily to their bedding raised the basal levels of plasma corticosterone in individually housed, virgin female mice, when compared with females (grouped or individually housed) living with male mice or with group-housed females exposed daily to male urine. Values were not affected during ether-induced stress. A single application of male urine raised plasma levels 30 min later regardless of housing conditions; but after 4 and 24 h levels had fallen to normal. The results are discussed in terms of sensitization of the pituitary-adrenal system and of stress and reproductive pheromones. Male urine was less effective than male presence at inducing 4-day oestrous cycles. Length and type of cycle varied continuously under the influence of a spectrum of environmental signals.