Puberty acceleration in mice. I. Dose-response effects and lack of critical time following exposure to male mouse urine.

Hybrid (SJL X SWR)F1 mice were used as the experimental animals in a uterine weight bioassay for puberty-accelerating pheromone of male mice. The bioassay was characterized with respect to age and weight of female mice, time factors and mode of pheromone administration. Advantages over previously used assays are: optimal assay time is short (48 h); a single application of male urine to the oronasal groove provides sufficient stimulus; and there is no seasonal variation. This bioassay was used to examine the pattern of response to serial, 10-fold dilutions of male urine and to determine whether there was a ‘critical time” for inhibition by ovulation-blocking agents following pheromonal stimulation. We found a unique dose-response pattern, with a maxi- mal uterine weight response at 10(cid:1) dilution of urine and no response at dilutions greaten than i0(cid:1). Dilute male urine was equally as effective as the presence of an intact male, leading us to the conclusion that stimuli other than male urine are not required for the full uterine weight response in F1 mice. Chlorpromazine, a centrally acting drug that blocks ovulation, inhibited the uterine weight response following exposure to male urine at all times studied. This suggests that the rhythmic pattern of hypothalamic activity characteristic of adult cycling mice is not established in prepubertal