Mean serum estradiol-17 concentration was variable but generally greater than 20 pg/ml during estrus in both mated and unmated queens. In the former group repeated matings elicited an LH response during the first 2 days of estrus (Days 1 and 2) in 10 of 12 queens. Two cats mated 3 times daily failed to produce an LH response until Day 2. On Day 1 mean LH rose from 4.3 ng/ml (0 h) to 50.4, 74.1, and 25.8 ng/ml at 4, 8, and 14 h, respectively. On Day 2, average LH changed from 10.3 ng/ml (0 h) to 27.7, 23.4, and 9.6 ng/ml at 4, 8, and 14 h, respectively. Generally no further increase in LH response was detected even though queens continued to mate. The initial rise in mean serum progesterone occurred on the morning of Day 4 or 64-68 h after the first detected LH peak. In five of 12 cases, ovulation was completed within 48-52 h of the LH peak. In the remaining seven cats, ovulation occurred 52 h or more after the LH peak but was completed in all animals by midafternoon on Day 5. Data from individual cats during estrus were similar to the average results; however, dramatic temporal fluctuations in steroid hormones, particularly estradiol-17 were often observed. Vesicular follicles were observed on the ovaries of individual cats during all stages of the luteal and interestrous interval. During these periods elevations in serum estradiol-17 above basal concentrations were occasionally detected particularly following the end of the luteal phase. During the latter phase, mean CL diameter increased gradually with elevations in serum progesterone; however, regression of visible luteal tissue was gradual with CL remnants remaining visible through the end of the interestrous interval.

In unmated queens the mean serum estradiol-17 profile during and after estrus was similar to the ovulating group. LH and progesterone were sustained at basal concentrations throughout these periods.

These data interrelate events of the reproductive cycle of the cat and suggest that 1) the mated estrual queen exhibits a gradual decline in pituitary LH response after repeated coitus; 2) "coitusto-ovulation" interval is an inappropriate parameter for this species since neither single nor multiple copulation always ensures an LH response and, thus, ovulation; 3) although follicular activity is greatest during estrus, periods of follicle growth and regression appear to occur continually even during the luteal phase.