Aldosterone decreases glucose-stimulated insulin secretion in vivo in mice and in murine islets

Abstract

Aims/hypothesis: Aldosterone concentrations increase in obesity and predict the onset of diabetes. We investigated the effects of aldosterone on glucose homeostasis and insulin secretion in vivo and in vitro. Methods: We assessed insulin sensitivity and insulin secretion in aldosterone synthase-deficient (As [also known as Cyp11b2]-/-) and wild-type mice using euglycaemic-hyperinsulinaemic and hyperglycaemic clamps, respectively. We also conducted studies during high sodium intake to normalise renin activity and potassium concentration in As -/- mice. We subsequently assessed the effect of aldosterone on insulin secretion in vitro in the presence or absence of mineralocorticoid receptor antagonists in isolated C57BL/6J islets and in the MIN6 beta cell line. Results: Fasting glucose concentrations were reduced in As-/- mice compared with wild-type. During hyperglycaemic clamps, insulin and C-peptide concentrations increased to a greater extent in As -/- than in wild-type mice. This was not attributable to differences in potassium or angiotensin II, as glucose-stimulated insulin secretion was enhanced in As-/- mice even during high sodium intake. There was no difference in insulin sensitivity between As-/- and wild-type mice in euglycaemic-hyperinsulinaemic clamp studies. In islet and MIN6 beta cell studies, aldosterone inhibited glucose- and isobutylmethylxanthine-stimulated insulin secretion, an effect that was not blocked by mineralocorticoid receptor antagonism, but was prevented by the superoxide dismutase mimetic tempol. Conclusions/interpretation: We demonstrated that aldosterone deficiency or excess modulates insulin secretion in vivo and in vitro via reactive oxygen species and in a manner that is independent of mineralocorticoid receptors. These findings provide insight into the mechanism of glucose intolerance in conditions of relative aldosterone excess. © 2011 Springer-Verlag.