Levels of LH in the sera and pituitaries of female lambs following ovariectomy and administration of estrogen.

Abstract

The concentration of LH in sera and pituitaries was determined by radioimmunoassay in 21 female lambs after ovariectomy and/ or administration of estradiol 17β (E2). At 5- days-of-age lambs were divided to form four groups. Lambs of Group C were controls, Group 0 were ovariectomized, Group E were implanted subcutaneously with E2 and Group OE were ovariectomized and given E2. The lambs were bled daily by venipuncture for 25 days after birth and then on alternate days until 44 days when they were killed. The LH in the serum of lambs in Group C and 0 began to increase to a level detectable by the assay when the lambs were 12 days of age. LH in the serum of Group C increased to 2-4 ng/ml when the lambs were 21–24– days-of-age but did not rise thereafter. Lambs of Group 0 had a sharp rise in LH in the serum beginning at day 12 which continued to day 44. The rise in LH in the serum of individual lambs of both Group C and 0 was not continuous from day to day as there were numerous cases of declining levels from one day to the next. The LH in serum of lambs in Groups E and OE, receiving 15-20 μg of exogenous E2 daily, remained below that of the sensitivity of the assay. The concentration of LH in the pituitaries of Group C was significantly greater (P < 0.001) than in groups 0, E and OE. The uteri in lambs of Group C were significantly heavier than those of Group O (P < 0.05), but were significantly lighter than those of Groups E and OE (P < 0.005). On the basis of this evidence we conclude that the ovarian-pituitary feedback system is functioning in lambs within a few days after birth, and that sufficient ovarian steroids are being synthesized and released to affect uterine growth but not to suppress release of LH. The rate of release of LH from the pituitary of the ovariectomized lamb is approximately equal to that of synthesis, hence there is little storage of LH. Administration of 15-20 μg of exogenous E2 daily, suppresses both synthesis and release of pituitary LH and increases uterine weight. (Endocrinology90: 981, 1972)