The effects of centrally applied somatostatin on the adrenal cortex of male rats

The effects of the intracerebroventricular (i.c.v.) administration of somatostatin (SRIF-14) on zona glomerulosa (ZG), zona fasciculata (ZF) and zona reticularis (ZR) of the adrenal cortex and an the blood concentrations of adrenocorticotropic hormone (ACTH), prolactin (PRL), growth hormone (GH), aldosterone, cortisol, progesterone and estradiol in male rats were studied. Each experimental animal was given three 1 mu g doses of SRIF-14 dissolved in 5 mu L saline by i.c.v. route every second day. Controls were treated in the same way with the same volume of saline. The rats were sacrificed by decapitation five days after the last SRIF-14 dose. The left adrenal gland of each animal was dissected and prepared for histological and morphometric analyses. Blood samples were collected for hormone level determinations. SRIF-14 led to a significant reduction (p < 0.05) of the absolute volume of the adrenal gland and of the volume of the cortex and ZG in comparison with the controls. Total number and volume of ZG cells and their nuclei was also significantly reduced (p < 0.05) in SRIF-14-treated rats as compared to the controls. There were no significant changes in morphometric parameters of ZF and ZR. At the same time, a significant decrease (p < 0.05) of aldosterone, GH, and PRL levels were observed, while the concentration of ACTH, cortisol, progesterone, and estradiol were almost unaltered in comparison with control values. It can be concluded that centrally applied SRIF-14 inhibits both the secretory activity and growth of adrenal ZG cells only, while insignificantly affecting ZF and ZR cells.