Release of FSH after administration of gonadotrophin-releasing hormone or estradiol to the anestrous ewe

The plasma FSH and LH responses to 17β–estradiol (E2) or to a synthetic gonadotrophin— releasing hormone (Gn—RH) were examined in anestrous ewes. FSH was measured by a heterologous double—antibody radioimmunoassay, while LH was estimated using a solid—phase method. Intravenous infusions of E2 (10 μg/hr for 4 hr) caused the plasma concentration of FSH to rise from 20–130 ng/ml NIH—FSH—S6 to peak values of 190, 350, and 400 ng/ml, respectively, in 3 animals. The release of FSH occurred over the same time interval as that previously reported for LH. In 2 animals, intracarotid infusions of Gn—RH (1.5 μg/hr for 3 hr) caused significant increases in both gonadotrophins which again rose and fell together. Plasma FSH concentrations rose from 38 and 70 ng/ml to a peak of 110 and 160 ng/ml after iy2 and 3 hr, respectively. These findings are consistent with the concept that Gn— RH is the mediator of the estrogen—induced release of LH and FSH which occurs at estrus. (Endocrinology 92: 862, 1973)