Location of thyrotropin-releasing hormone-like immunoreactivity in rat pancreas.

The location of TRH-like immunoreactivity (TRH-LI) was determined in developing rat pancreas (20.5 and 22.5 days of gestation, 1, 3, and 8 days, and 3 months after birth). The pancreatic tissue was freeze-dried and fixed in acrolein or paraformaldehyde vapor, and paraffin sections (2 microns) were prepared for immunostaining. TRH-LI was detected only in the islets. On day 20.5 of gestation, a few cells contained TRH-LI. During development, cells bearing TRH-LI increased in number and were most numerous in the early neonatal period (1-3 days). Then their number decreased again from 8 days after birth; in adult rats the immunoreactivity was too weak to allow identification of TRH-LI-positive cells. The topographical relation of TRH-LI with other islet hormones was studied in serial sections from perinatal rats stained with different antisera. TRH-LI was found in almost all cells containing insulin and in some containing glucagon, but not in those containing somatostatin.