Summary. LH release leading to ovulation was induced in 17 of 29 oestrous periods. The time of ovulation after coitus was determined by histological examination or by observation at laparotomy of ovaries in situ. Histological methods revealed that ovulation was complete in most follicles (9 of 13) at 32 h post coitum and in all follicles that were involved in the ovulatory process by 36 h. When laparotomy was used, no signs of preovulatory change were noted at the first observation time, 22 h post coitum, but in 4 cycles in which the entire process of ovulation was observed, the ovulatory process occurred between 23 and 28 h (3 follicles), 23 and 27 h (2 follicles), 25 and 28 h (3 follicles), and 25 and 29 h (3 follicles)post coitum. The first ovulatory process noted was complete at 25 h post coitum.
In cats, LH release continued over a 16-h period before returning to baseline (long surge), values being 616 ± 180 ng/ml at ½ h and 941 ± 154 ng/ml at 2 h post coitum. In 6 cats the LH release pattern was limited to a 4-h period (short surge), values being 537 ± 218 ng/ml at ½ h and 353 ± 245 ng/ml plasma at 2 h and basal (49 ± 18 ng/ml) by 4 h post coitum. Decreased secretion of oestrogen by follicles in animals undergoing ovulation was first observed at 16 h post coitum.
It is concluded that coitus induces LH release within minutes in the cat and that ovulation begins about 24 h later and finishes by about 32 h post coitum. Only one coital input can cause LH release for as long as 16–20 h although shorter periods of LH release (4 h or less) can result in ovulation.