Glucocorticoids modulate baroreflex control of renal sympathetic nerve activity

Experiments were performed to determine the effects of glucocorticoids on a rterial baroreceptor reflex control of renal sympathetic nerve activity (RS NA). Intravenous infusions of phenylephrine and nitroprusside were used to produce graded changes in arterial pressure (AP) in Inactin-anesthetized ma le Sprague-Dawley rats. Baroreflex control of RSNA was determined during a baseline period and 2 and 3 h after administration of the glucocorticoid ty pe II receptor antagonist Mifepristone (30 mg/kg sc) or vehicle (oil). Cort icosterone (cort) treatment (100 mg cort pellet sc for 2-3 wk) increased ba seline AP from 115 +/- 2 to 128 +/- 1 mmHg. Cort treatment also decreased t he gain coefficient and increased the midpoint of the baroreflex curve. Tre atment of cort rats with Mifepristone decreased AP within 2 h and increased the gain coefficient and decreased the midpoint of the baroreflex function curve back toward values measured in control rats. Mifepristone altered th e baroreflex function curve even when AP was maintained at baseline levels. Therefore, these data demonstrate for the first time that glucocorticoids can modulate baroreflex control of RSNA by a mechanism that is, in part, in dependent of changes in AP.