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Endocrinology, Vol 100, 1294-1302, Copyright © 1977 by Endocrine Society

ARTICLES

Effect of in vivo treatment with estrogen on luteinizing hormone synthesis and release by rat pituitaries in vitro

TC Liu and GL Jackson

The influence of estrogen on uptake of [3H]glucosamine and [14C]alanine and their incorporation into LH and total protein was investigated. Ovariectomized rats were sacrificed 22 h after injection with either oil or estradiol benzoate (EB, 50 microng/rat). Quartered anterior pituitary glands were incubated for 4 h with radioactive precursors in the presence or absence of 3.6 X 10-8M synthetic gonadotropin-releasing hormone (GnRH). Labeled LH was isolated by immunoprecipitation with specific anti-LH-beta serum. Both EB and GnRH significantly elevated the amount of [3H]glucosamine-LH appearing in the medium, the tissue, and the total system (medium + tissue), but they increased the amount of [14C]alanine-LH only in the medium. There was a significant positive interaction between EB and GnRH on the amounts of [3H]glucosamine-LH and [14C]alanine-LH in the medium and of [3H]glucosamine-LH in the tissue and total system. EB enhanced [3H]glucosamine uptake and incorporation into total protein, but GnRH had little or no effect on these parameters. In time course studies rats were injected with either oil or EB at 22, 11, or 5.5 h prior to sacrifice. At all times EB significantly increased synthesis and release of [3H]-glucosamine-LH and release of total immunoreactive LH (IR-LH) by pituitaries incubated with GnRH. The amounts of labeled and IR-LH released into the medium increased linearly with time after EB injection, but the amount of labeled LH in the total system plateaued at 5.5 h after EB injection. In another study, estradiol (E2, 5 microng/rat) dissolved in 1% ethanol- saline was injected at 0.5, 1.0, 2.0, or 4 h prior to sacrifice. Incorporation of [3H]glucosamine into tissue protein and release of [3H]glucosamine-LH was stimulated within 2 h after E2 injection. However, incorporation of [3H]glucosamine into LH was not stimulated until 4 h after E2 injection. These results suggest that estrogen and GnRH regulate LH synthesis at different sites, and that the effect of estrogen is non-specific compared to that of GnRH. The synthesis of the carbohydrate moiety of LH appears to be subjected to hormonal regulation more readily than the synthesis of the polypeptide moiety.




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Copyright © 1977 by The Endocrine Society