Stimulation of14C-glucosamine andl4C-alanine Incorporation Into Thyrotropin by Synthetic Thyrotropin-Releasing Hormone

Abstract

The influence of synthetic thyrotropin releasing hormone (pyro-L-glutamyl-L-histidyl- L-proline amide, Abbott Laboratories) upon thyrotropin (TSH) biosynthesis was investigated. Rat hemipituitaries were incubated in vitro with ¹⁴C-l-glucosamine and ¹⁴C-alanine. TSH formation rates were assessed by measurement of precursor incorporation into TSH, isolated by immunoprecipitation with specific anti-TSH sera. TRH significantly enhanced ¹⁴C-glucosamine and ¹⁴C-alanine entry into TSH as well as stimulating an increase in the total amount of TSH released during a 24-hr incubation period. TRH exerted much less stimulation upon synthesis after only 6 hrs, suggesting that the augmentation of TSH synthesis attending TRH stimulation is delayed relative to secretion. When TSH secretion mediated by TRH was inhibited by adding L-thyroxine to or omitting calcium from the incubation medium, TRH stimulated a small rise in intrapituitary ¹⁴C-TSH. The possibility that TRH may exert a stimulatory influence upon TSH synthesis independently of TSH secretion is discussed. (Endocrinology89: 873, 1971)