The effect of triiodothyronine (T3) and thyroxine (T4) upon insulin secretion from isolated rat pancreatic islets.

In order to observe the effect of triiodothyronine (T3) or thyroxine (T4) on glucose-induced insulin release from pancreatic islets, isolated pancreatic islets from Wistar male rat were incubated in modified Krebs-Ringer bicarbonate solution (0.2% BSA, pH 7.4) with 3 mM, 5 mM or 10 mM glucose for 60 min with or without exposure to T3 (2.5 micrograms/ml or 7.5 micrograms/ml) or T4 (2.5 micrograms/ml or 7.5 micrograms/ml). Direct exposure of isolated pancreatic islets to T3 or T4 did not have any effect on glucose-induced insulin release from pancreatic islets during 60 min incubation. But, in successive 60 min incubations following 60 min rest periods after exposure to T3 or T4 in the first incubation, glucose-induced insulin release from isolated pancreatic islets previously exposed to T4 was reduced at 5 mM and 10 mM glucose concentrations and previous exposure to T3 had no effect on glucose-induced insulin release. A delayed effect of T4 on the mechanism of insulin secretion from pancreatic islets was suggested.