Effects of centrally applied somatostatin on pituitary adrenocorticotropes in female rats
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Effects of intracerebroventricular (i.c.v.) application of somatostatin (SRIH-14 or SRIH-28) on growth and function of pituitary adrenocorticotropes (ACTH cells) were examined in adult female Wistar rats. Animals were subjected to i.c.v. administration of three 1-mu g doses of SRIH-14 or SRIH-28 dissolved 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 injection, 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 para meters occurred after SRIH-14 treatment. Plasma concentration of ACTH in SRIH-28-treated rats was significantly lower (p < 0.05) than in control rats by 35%. In SRIH-14-treated rats, plasma concentration of ACTH was slightly, but not significantly (p > 0.05) increased by 13% compared to saline treatment. These observations suggest that centrally administered somatostatin-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 affect ACTH activity without altering actions usually attributed to receptors sensitive to SRIF-14. Copyright (C) 2000 S. Karger AG, Basel.