Both 3,5-diiodo-L-thyronine (T2) and T3 modulate glucose-induced insulin secretion

Area of Science:

• Endocrinology
• Metabolism
• Cell Biology

Background:

• Thyroid hormones, including 3,5-diiodo-L-thyronine (T2) and triiodothyronine (T3), influence various physiological processes.
• The specific effects of T2 on pancreatic beta-cells, which regulate insulin secretion, remain largely uncharacterized.
• Understanding these effects is crucial for metabolic research and potential therapeutic strategies.

Purpose of the Study:

• To investigate the impact of T2 and T3 on glucose-induced insulin secretion.
• To compare the effects of T2 and T3 on both rodent (INS-1e) and human pancreatic beta-cells.
• To determine the dose-dependent and glucose-level-dependent actions of these iodothyronines.

Main Methods:

• INS-1e cells and human islets were incubated with varying concentrations of T2 and T3.
• Cells and islets were exposed to different glucose concentrations (3.3 to 20 mmol/L).
• Insulin secretion and content were measured to assess the hormonal effects.

Main Results:

• Both T2 and T3 demonstrated a biphasic effect on insulin secretion, stimulating at lower concentrations and inhibiting at higher concentrations.
• T2 (1-100 nmol/L) and T3 (0.1 nmol/L-1.0 μmol/L) significantly stimulated insulin release and content in INS-1e cells.
• In human islets, T2 (0.1 nmol/L-0.1 μmol/L) significantly enhanced insulin secretion, while higher concentrations inhibited it.

Conclusions:

• T2 and T3 exert a direct regulatory influence on insulin secretion from pancreatic beta-cells.
• The effects are concentration-dependent and modulated by ambient glucose levels.
• Physiological concentrations of T2 appear to enhance glucose-induced insulin secretion, highlighting a potential role in glucose homeostasis.