Brain mineralocorticoid receptor control of blood pressure and kidney function in normotensive rats

Brain mineralocorticoid receptors appear to contribute to mineralocorticoid hypertension and may be involved in blood pressure control in normotensive rats. We; examined the effect of blockade of central mineralocorticoid rec eptors with the use of a selective antagonist (RU28318) on cardiovascular a nd renal function in conscious normotensive rats. The contribution of renal innervation was evaluated in rats with bilaterally denervated kidneys. You ng adult, male Wistar rats were trained for systolic blood pressure measure ment by a tail sphygmographic method and accustomed to metabolic cages for collection of urine. One week before experimentation, an intracerebroventri cular cannula was implanted. Systolic blood pressure was diminished 30 minu tes after an intracerebroventricular dose of 10 ng of RU28318, The effect w as maximal at 8 hours and was still present after 24 hours. Blood pressure returned to the basal level by 48 hours. During the period 0 to 8 hours aft er intracerebroventricular injection, rats treated with the antagonist show ed an increase in diuresis and urinary electrolyte excretion. No significan t effect on plasma renin activity, measured 8 and 30 hours after administra tion of RU28318, was observed. In denervated rats, the decrease in systolic blood pressure after administration of RU28318 was reduced. The difference was statistically significant compared with controls at 2 hours but not at 8 hours, and blood pressure returned to the basal value by 24 hours. The i ncreases in diuresis and urinary electrolyte excretion induced by RU28318 w ere abolished in denervated rats. These results show that brain mineralocor ticoid receptors are involved in blood pressure regulation and kidney funct ion homeostasis in conscious normotensive rats. The renal nerves appear to participate in the brain mineralocorticoid receptor control of blood pressu re.