Comparison of pancreatic and hypophysiotropic TRH systems.

The thyrotropin-releasing hormone (TRH) is a molecule with widespread distribution through many organ systems. The function of TRH is probably not identical in each system so that TRH synthesis and secretion may be unique for each system under specific experimental conditions. The present study was designed to explore the common and diverse features of the regulation of TRH encoded with the same gene in two different organs: hypophysiotropic hypothalamus and pancreatic islets. During in vitro incubation, the TRH content in hypothalamic structures remained stable while that in isolated pancreatic islets increased sharply. In contrast to the pancreatic islets, exposure to different concentrations of D-glucose did not affect TRH release from the hypothalamic paraventricular nucleus or median eminence. This divergence in the regulation of the hypophysiotropic and pancreatic TRH systems may be related to differences in the role of TRH produced in these tissues.