Presumed involvement of pheromones in mating behavior in the rat

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Eighty-one 3–4 month-old female Wistar rats (W II strain of our colony) were exposed to the odor of male urine from the onset of the 3rd cycle of a regular sequence of 5-day cycles. Forty-two 5-day cyclic females served as controls. A shortening of the estrous cycle duration to 4 days due to an advanced ovulation was evidenced in 50.6% of the urine-treated females while it occurred in 5% of the control females only ( p < .001). The following patterns were observed in treated animals: 5,5,4,4 ( 12 81 )-5, 5,5,4, ( 23 81 )-5,5,4,5 ( 6 81 ). A lengthening of the cycle was evoked by the odor of male urine in 2.4% of the cases. No statistically significant difference was established between the control females and those of the treated females which maintained a 5-day cyclicity regarding their ability to mate precociously during the night following Day 3 of 5-day cycles (diestrus 3 to proestrus) ( 7 40 and 3 38 , respectively). The male estrous acceptance during the night following the day of proestrus was similar in experimentally induced 4-day cycles ( 11 19 ) and in control 4-day cycles ( 24 30 ) ( p >0.25). These results suggest that pheromones may stimulate the gonadotropic function of the pituitary in the rat. They also suggest that olfactory stimuli do not directly activate the neural structures necessary for early mating behavior in the 5-day cyclic females of the strain used in the present experiments.