Some observations concerning the role of progesterone in the control of ovulation

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Abstract
Pre-ovulatory LH[luteinizing hormone]-surges in 4 day cyclic rats (4d-r) were postponed 1, 4 or 8 days by treatment with progesterone (P), or 1 day by treatment with pentobarbitone just prior to the onset of the critical period on proestrus. P-delayed LH-surges tend to become higher with increasing duration of the preceding anovulatory period: 1 day-delayed surges were as high as 5d-r surges (i.e., about twice as high as spontaneous 4d-r surges); 8 days-delayed surges were significantly higher. Compared with 4d-r surges the time of onset and zenith of P-delayed surges is significantly advanced. The 1 day-P-delayed surges too were as high as 5d-r surges, but still timed as 4d-r surges. On no artificial proestrus day did the responsiveness of the pituitary differ from the normal proestrus responsiveness. P may influence the timing but not the height of pre-ovulatory LH-surges.