The morphological effects of dexamethasone on the pituitary-adrenal axis of the rat--a quantitative study.

Adult Sprague-Dawley rats received a daily intraperitoneal injection of dexamethasone (100 or 200 micrograms/kg) for 2 or 6 weeks. Quantitative assessment of the anterior pituitary corticotroph population performed using the stereological measurement of volume density (Vv). An indirect assessment of corticotroph function was also made, based on adrenal weight and histology. Adrenal changes were consistent with dose-related inhibition of corticotroph function in all dexamethasone-treated animals. Immunopositive corticotrophs were easily identified and in no treatment group was corticotroph Vv significantly less than in the appropriate vehicle-injected control group. In male animals, there was a significant increase (P less than 0.05) in Vv with 100 micrograms/kg at both 2 and 6 weeks. These results suggest that it is possible to produce inhibition of corticotroph function by the administration of such doses of dexamethasone without causing a significant reduction in the anterior pituitary corticotroph population. This may be related to the mode of negative feedback of such a regime.