Effects of neurotensin on the pituitary-adrenocortical axis of intact and dexamethasone-suppressed rats.

A 7-day infusion with neurotensin (NT) (10 micrograms.kg-1.day-1) stimulated adrenal growth in intact female rats, and raised ACTH blood concentration, without altering corticosterone (B) plasma level and output by adrenal homogenates. For a week dexamethasone (Dx) administration (125 micrograms.kg-1.day-1) caused a notable adrenal atrophy, a marked lowering of ACTH and B blood concentrations, and a profound depression of B output by adrenal homogenates. NT infusion reversed Dx-induced adrenal atrophy and plasma ACTH-level drop, but not the impairment in adrenal-cortex secretory activity. In vitro studies showed that NT (10(-6) mol/l) significantly reduced basal, but not ACTH-stimulated B release by isolated rat inner adrenocortical cells. These findings suggest that NT exerts a direct inhibitory effect on B production by rat adrenals, while it is able to enhance ACTH secretion and consequently adrenal growth. Moreover, they indicate that NT evokes a striking, and at present unexplained dissociation between structure and function in the adrenal cortex of Dx-suppressed rats.