Effects of synthetic gonadotropin-releasing hormone on incorporation of radioactive glucosamine and amino acids into luteinizing hormone and total protein by rat pituitaries in vitro

Abstract

The influence of synthetic gonadotropin-releasing hormone (GnRH) on incorporation of glucosamine and amino acids into LH and total protein was investigated. Rat pituitaries were incubated in vitro with radioactive precursors for 4 h at 37 C. Labeled LH was isolated by immunoprecipitation with specific anti-LH-beta serum. Total LH in the medium and pituitary glands was measured by radioimmunoassay. GnRH significantly stimulated incorporation of [3H]glucosamine into LH in pituitaries from immature male, intact female, and ovariectomized rats. Pituitaries from ovariectomized rats synthesized more [3H]glucosamine-labeled LH than those from intact adult rats. GnRH enhanced release of [3H]glucosamine-LH into medium in pituitaries of both adult intact and ovariectomized rats. The response to GnRH was greatly reduced when pituitaries were exposed to cold shock before the 4 h incorporation period. In contrast to its effect on incorporation of [3H]glucosamine into LH, GnRH had either no or little effect, depending on experimental conditions, on uptake of [3H]glucosamine by pituitaries. Incorporation of [3H]glucosamine into total protein was not affected by GnRH treatment. GnRH increased release of either [3H]leucine- or [3H]alanine-labeled LH into medium, but had no significant effect on incorporation of labeled amino acids into total LH in the system. GnRH modified neither uptake nor incorporation of amino acids into total protein. GnRH significantly stimulated the release of cold LH into medium under all conditions, but the total amount of immunoassayable LH in the system was not detectably modified by GnRH treatment.