Localization of thyrotropin-releasing hormone- and insulin-immunoreactivity in the pancreas of neonatal rats after injection of streptozotocin at birth.

Streptozotocin treatment at birth induces, in the pancreas of rats, first depletion of insulin and thyrotropin-releasing hormone and then early regeneration of beta cells and insulin, but not TRH. This study was undertaken to investigate whether the reduction in pancreatic TRH content can be associated with changes in the intensity and the distribution of TRH-immunoreactivity, and to follow the pattern of regeneration of beta cells through insulin- and TRH-immunoreactivity. In control animals, strong TRH-immunoreactivity was seen in insulin-containing cells on days 1-4 after birth. At day 7, the TRH-immunoreactivity was already decreased. In contrast, insulin-immunoreactivity was present throughout the neonatal period. A sparse population of cells near ducts also contained both TRH- and insulin-immunoreactivity at 1-2 days age. In streptozotocin-treated animals, TRH-immunoreactivity is found only in a few scattered insulin-containing cells in altered islets on days 1-4. Near the ducts, there were new insulin-containing cells which did not contain TRH. From day 7 regeneration of endocrine cells was characterized by new, typical islets, but these contained insulin- but not TRH-immunoreactivity. These findings suggest a differential control of the biosynthesis of insulin and TRH within the pancreas.