HORMONAL MECHANISMS INVOLVED IN THE CONTROL OF OESTROUS CYCLE DURATION BY THE ODOUR OF URINE IN THE RAT

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Abstract
The mechanisms involved in the reduced cycle duration following exposure to the odor of urine were studied in natural and experimental 5-day cyclic female Wistar rats. A decrease in the rate of ovarian progesterone [P4] secretion from the morning of diestrus I to that of diestrus II was observed in females whose cycle duration was reduced from 5 to 4 days following exposure to the odor of rat urine. No decrease in ovarian P4 secretion occurred in females maintaining a 5-day cyclicity despite exposure to this odor. An increase in follicular growth was noted in females with cycle duration reduced from 5-4 days, when compared with those maintaining a 5-day rhythm. As a result of exposure to the odor of urine no reduced cycle duration occurred in females with cycles lengthened from 4-5 days as a result of P4 injection on diestrus I of 4-day cycles. The decrease in ovarian progesterone secretion, induced by exposure to the odor of urine, is considered to cause a speeding up in follicular growth, thereby reducing estrous cycle duration in 5-day cyclic rats.