Many lines of evidence have shown that
preproglucagon-derived
peptides affect
steroid secretion from dispersed adrenocortical cells, and that
streptozotocin (STZ)-induced experimental diabetes alters adrenocortical-cell function. Hence, we compared the effects of
glucagon,
glucagon-like peptide (GLP)-1 and GLP-2 on basal and
ACTH-stimulated secretion of dispersed adrenocortical cells from normal and STZ-induced diabetic rats. We also examined the effects of exendins (EX) 3 and 4, because EX4 is known to be a potent and long-lasting agonist of
GLP-1 receptors. STZ-induced diabetes moderately enhances basal and
ACTH-stimulated secretion from dispersed zona glomerulosa (ZG) cells, without significantly affecting
corticosterone production from dispersed zona fasciculata-reticularis (ZF/R) cells. In normoglycemic rats,
glucagon increased basal
aldosterone and
corticosterone secretion from ZG and ZF/R cells, GLP-2 raised both basal and
ACTH-stimulated
aldosterone secretion and
ACTH-stimulated
corticosterone output, and EX4 increased basal
corticosterone secretion. In contrast,
glucagon, GLP-2 and EX4 did not elicit secretory responses from adrenocortical cells of diabetic rats.
GLP-1 and EX3 did not alter secretion of dispersed adrenocortical cells of either normal or STZ-treated rats. Taken together, our findings indicate that
preproglucagon-derived
peptides enhance
steroid secretion from adrenocortical cells of normal, but not STZ-induced diabetic rats. It is suggested that the prolonged exposure to low concentrations of
insulin causes unresponsiveness of adrenocortical cells to
glucagon, GLP-2 and EX4, which may contribute to the
hyporeninemic hypoaldosteronism and alterations in
glucocorticoid metabolism occurring in experimental diabetes.