Inhibitory effects of centrally administered somatostatin on the adrenal zona glomerulosa in male rats.

This study examined the effects of intracerebroventricularly administered somatostatin (SRIF-28 and SRIF-14) on growth and steroidogenic capacity of the rat adrenal zona glomerulosa. Male adult Wistar rats were subjected to intracerebroventricular administration of three 1 microgram doses of SRIF-28 or SRIF-14 every other day. Five days after the last dose, the rats were sacrificed by decapitation. Blood samples were collected for hormonal analyses, and left adrenal glands were taken for histological and morphometric evaluation. In comparison with control animals, the SRIF-treated rats had decreased (p < 0.05) adrenal gland weight and volume. Stereological and morphometric analyses showed decreased (p < 0.05) absolute and relative volumes of the cells and nuclei only in the zona glomerulosa. The plasma levels of aldosterone, growth hormone, and prolactin in both SRIF-treated groups were lower (p < 0.05) than in the control group. The levels of adrenocorticotropic hormone after SRIF treatment did not differ significantly from those in control rats. These findings suggest that centrally administered somatostatin is specifically involved in the control of zona glomerulosa growth and secretion; this effect is probably mediated by inhibiting the secretion of the corresponding pituitary hormones.