Effects of centrally applied somatostatin on pituitary adrenocorticotropesin female rats

Effects of intracerebroventricular (i.c.v.) application of somatostatin (SR IH-14 or SRIH-28) on growth and function of pituitary adrenocorticotropes ( ACTH cells) were examined in adult female Wistar rats. Animals were subject ed to i.c.v. administration of three 1-mu g doses of SRIH-14 or SRIH-28 dis solved in 5 mu l saline every second day, Controls were treated in the same way with the same volume of saline only, ACTH-producing cells were studied using the peroxidase-anti peroxidase (PAP) immunohistochemical procedure; blood samples were collected for hormone analyses 5 days after the last inj ection, SRIH-28 treatment decreased (p < 0.05) all morphometric parameters compared to control rats. Volume of ACTH cells decreased by 10%, nuclei by 36% and volume density by 13%, No significant changes (p > 0.05) in these p ara meters occurred after SRIH-14 treatment. Plasma concentration of ACTH i n SRIH-28-treated rats was significantly lower (p < 0.05) than in control r ats by 35%. In SRIH-14-treated rats, plasma concentration of ACTH was sligh tly, but not significantly (p > 0.05) increased by 13% compared to saline t reatment. These observations suggest that centrally administered somatostat in-28, but not somatostatin-14, is specifically involved in the control of growth and secretory activity of ACTH cells in female rats, Thus, selective pharmacological manipulation of SRIH-28 receptors reached from CSF may aff ect ACTH activity without altering actions usually attributed to receptors sensitive to SRIF-14. Copyright (C) 2000 S. Karger AG, Basel.