Effect of in Vivo Treatment with Estrogen on Luteinizing Hormone Synthesis and Release by Rat Pituitaries in Vitro

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Abstract
The influence of estrogen on uptake of 3H-glucosamine and 14C-alanine and their incorporation into LH [luteinizing hormone] and total protein was investigated. Ovariectomized rats were sacrificed 22 h after injection with either oil or estradiol benzoate (EB, 50 .mu.g/rat). Quartered anterior pituitary glands were incubated for 4 h with radioactive precursors in the presence or absence of 3.6 .times. 10-8 M 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. 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 .mu.g/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. Incorporation of 3H-glucosamine into LH was not stimulated until 4 h after E2 injection. Estrogen and GnRH probably regulate LH synthesis at different sites, and the effect of estrogen is probably 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.