Streptozotocin treatment at birth induces a parallel depletion of thyrotropin-releasing hormone and insulin in the rat pancreas during development

Abstract

Elevated concentrations of TRH have been detected in the rat pancreas during the early days of life. The purpose of this study was to investigate further the cellular location of this peptide in the pancreas using streptozotocin (STZ) injected at birth. Pancreatic TRH and insulin contents were measured at different ages from birth until 35 days in rats injected with STZ and results compared with controls injected with the vehicle. A transitory hyperglycemic state was observed from day 1 to day 5 (maximum value 2.9 +/- 0.31 g/liter). After this period, although slightly hyperglycemic, STZ rats were not glucosuric . TRH and insulin contents followed two distinct patterns from days 1 to 5 and days 5 to 35. During the first period, an acute depletion of both substances was observed, the lower value observed reaching 2.7% and 9% of control values, respectively, for TRH and insulin. The TRH surge at day 2 was blunted. During the second period, insulin content increased to reach 42% of controls. On the contrary, recovery of TRH was not observed; TRH content was 9% of control at day 35. These results indicate that TRH is located in STZ-sensitive cells, in agreement with recent immunohistochemical data. The impaired capacity for TRH recovery remained unexplained and seems to indicate a difference in the biogenesis of insulin and TRH.