The Effect of Triiodothyronine (T₃) and Thyroxine (T₄) upon Insulin Secretion from Isolated Rat Pancreatic Islets

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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 3mM, 5mM or 10mM glucose for 60min with or without exposure to T₃ (2.5μg/ml or 7.5μg/ml) or T₄ (2.5μg/ml or 7.5μg/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 5mM and 10mM 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.