Suppressive Effect of Dexamethasone on the Rise of CRF Activity in the Median Eminence Induced by Stress

Abstract

The present paper described the blocking effect of dexamethasone on stress-induced rises of CRF activity in the median eminence and of the corticosterone level in the peripheral blood. The stress used was laparotomy with intestinal traction. Two doses of dexamethasone (25 and 250 μg/100 g) were given intraperitoneally 1, 3, 6, 12, and 20 hr prior to the application of the stress. CRF activity in the crude extract of the median eminence was estimated by the intrapituitary microinjection technique. The pattern of suppressive effect of dexamethasone on the response of CRF activity to the stress was similar to that of plasma corticosterone at various time intervals between dexamethasone and stress. Dexamethasone in the larger dose (250 μg/100 g) produced no greater blockade than the smaller dose (25 μg/100 g) during the initial 6 hr period after injection, but in the following 12-20 hr period the former proved to cause a greater blockade than the latter. Therefore, the duration of blockade was related to the dose of injected corticoid. In addition, the pituitary gland in the assay rats pretreated with 50, 200, and 1000 μg/100 g of dexamethasone responded to extracts of the median eminence to a similar extent irrespective of the dexamethasone dose given. These findings suggest that the site of the inhibiting action of dexamethasone may be mainly at or above the hypothalamic level. (Endocrinology89: 1014, 1971)