Effects of urine from pregnant and lactating female house mice on sexual maturation of juvenile females

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Abstract
The effects of urine from pregnant and lactating female mice on puberty in young females were examined. In Experiment I urine from pregnant or lactating females painted daily on the external nares of young females led to earlier sexual maturation than treatment with water or urine from singly-caged, nonlactating, multiparous adult females. In Experiment II urine from either pregnant or lactating females, injected daily into perforated plastic capsules containing cotton, effected earlier maturation in female mice caged with these capsules than did the urine of singly-caged females or water. In Experiment III the effectiveness of these treatments on reproduction per se was confirmed: young females reaching maturity earlier as the result of urine treatments were in fact ovulating and were capable of conceiving and bearing young. One explanation for the presence of the urinary pheromone(s) involves changes in hormone levels during pregnancy and/or lactation and urinary excretion levels of hormones, hormone metabolites, or chemical compounds which are hormone dependent. The pheromone excretion, triggered by external factors, may be a general signal to other females that environmental and/or social conditions are favorable for reproductive activities.