The mitogenic effects of corticotrophin-releasing factor on the anterior pituitary gland of the rat.

The immunohistochemically defined corticotroph population in the anterior pituitary gland of the adult male Sprague-Dawley rat has been quantified at 2 and 6 weeks after bilateral adrenalectomy using the stereological measurement, volume density (Vv). An approximately twofold increase in corticotroph Vv was demonstrated at 2 weeks in adrenalectomized rats compared with that in sham-operated controls and this was maintained at 6 weeks. Daily i.p. injections of ovine corticotrophin-releasing factor (CRF-41) induced a significant dose-related increase in corticotroph Vv when administered at doses of 25 and 50 micrograms/kg body weight, but this was less than the increase following adrenalectomy. Assessment of changes in mitotic activity of the total anterior lobe of adult Sprague-Dawley rats and of the corticotroph population was also made after daily i.p. injections of 50 micrograms CRF-41/kg for 2 and 7 days. There was no increase in overall mitotic index at either time. However, the numbers of mitotic corticotrophs were significantly increased in CRF-injected animals compared with those in saline-injected rats. These results indicate a role for CRF-41 in the regulation of corticotroph growth.