Reflex LH Release in Estrous Cats Following Single and Multiple Copulations

Abstract

The nature of copulation-induced LH release in the domestic cat was assessed by measuring serum LH levels during each of 60 estrous periods studied in 13 animals. LH was measured by radioimmunoassay in serum samples collected at −48, −24, 0, 0.17, 1, 4, 8, and 24 h after copulation or contact with a male. The queens were permitted either 1 copulation (n=18), 4copulations during a 21–81 min period (n=23), ad libitum (8–12) copulatory activity for 4 h (n=13), mounting without intromission (n=4) or no mounting (n=2). The subsequent occurrence of reflex ovulation was determined by radioimmunoassay of luteal phase serum progesterone levels. The incidence of ovulation in trials involving zero, single, and multiple copulations was 0%, 50%, and 100%, respectively. At 10 min after copulation, LH levels in ovulating cats (17 ± 2 ng/ml) were higher (P<0.05) than the levels (8 ± 2 ng/ml) observed at 10 min in the nonovulating once-mated cats. LH levels at 1 h in ovulating once-mated cats (34 ± 9 ng/ml) were lower (P<0.05) than LH levels present at 1 h in cats allowed multiple matings (73 ± 11 ng/ml). Peak levels of LH occurred at 1–4 h in cats copulating 8–12 times in a 4 h period, and were higher (P<0.05) than those in cats permitted only 4 copulations (121 ± 24 vs 89 ± 15 ng/ml). LH levels had returned to baseline at 4 h in nonovulating once-mated cats (1.6 ± 0.4 ng/ml). Levels remained elevated until 8 h in ovulating cats and were lower (P<0.05) in once-mated cats (9 ± 3 ng/ml) than in cats mated 4–12 times (28 ± 4 ng/ml). At 24 h, levels were basal in all treatment groups. The results suggest that 1) LH release in cats ovulating in response to one copulation is similar in magnitude and duration to that reported in rabbits, 2) ovulation failure in some once-mated cats is due to inadequate LH release, and 3) the magnitude and duration of LH release, in cats allowed to copulate at natural intervals, are dependent on the number of copulations.