DIOESTROUS PROGESTERONE AND PRO-OESTROUS LUTEINIZING HORMONE IN 4- AND 5-DAY CYCLES OF FEMALE RATS

in Journal of Endocrinology
Authors:
P. VAN DER SCHOOT
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W. J. DE GREEF
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SUMMARY

Female rats which showed 5-day ovarian cycles spontaneously, but 4-day cycles for periods of variable length after induction of pseudopregnancy, were examined. While the time of onset of the ovulatory LH surge at pro-oestrus was the same in both 4- and 5-day cycles, dioestrous progesterone concentrations were dissimilar. The most prominent feature was a sharp increase during the night of the first day of dioestrus of the 4-day cycles. The results are interpreted as suggesting that dioestrous steroid concentrations rather than pro-oestrous LH concentrations are important in establishing cycle duration.

 

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