Effects of equimate (ICI-81008) on levels of luteinizing hormone, follicle-stimulating hormone and progesterone during the estrous cycle of the mare.

Jugular blood was collected at 6-hr intervals during estrus and at daily intervals during diestrus from 12 cycling mares. On day 8 of diestrus four mares were given saline (im) while the remaining eight mares were given Equimate (250 //g), a synthetic analog (ICI-81008) of PGF2c~. Following treatment, jugular blood was collected at 15-min intervals for 6 hr and "then at 6-hr intervals until the end of the subsequent estrus. Blood was again collected at daily intervals until the end of the diestrus following treatment. Day of ovulation was estimated by palpation per rectum. Serawere analyzed for LH, FSH and progesterone by radioimmunoassay. Injection of Equirnate on da3~ 8 of diestrus resulted in an immediate increase in levels of LH and FSH in serum. Concentrations of LH increased from 35.6 -+ 8.2 ng/ml to 89.8 -+ 25.2 ng/ml (P<.05) within 45 min after injection but had returned to baseline within 3 hours. Concentrations of FSH increased from 178 + 34 rig/ ml to 382 -+ 86 ng/ml (P<..05)within 45 min after the injection and then returned to baseline over the next several hours. Concentrations of progesterone decreased to baseline (< I rig/ ml) within 24 hr after Equimate and remained low until the end of the next estrus. Concentrations of LH and FSH during the estrus preceding Equimate and the estrus subsequent to Equimate did not differ (P>.05). Likewise, there was no difference (P>.05) between levels of progesterone during the diestrous periods of the cycles preceding, and subsequent to, Equimate. Similarly, concentrations of LH, FSH and progesterone were not different (P>.05) be-