Regulation of Blood Pressure by Sympathetic Nerve Fibers and Adrenal Medulla in Normotensive and Hypertensive Rats

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Abstract
The respective roles of the sympathetic nerve fibers and adrenal medulla in the regulation of blood pressure and heart rate were studied in normotensive and hypertensive rats. Chemical sympathectomy alone, by treatment with 6-OH-DA, or bilateral adrenalectomy reduced blood pressure only slightly in normotensive animals. In animals made hypertensive with deoxycorticosterone (DOCA) and saline, each of these procedures reduced blood pressure to a greater extent than in normotensive animals, but the blood pressure remained at hypertensive levels. The combination of both procedures resulted in a greater fall in blood pressure than could have been predicted from individual effects, suggesting that the removal of one component of the sympathetic system can be compensated for by a hyperactivity of the remaining component. After chemical sympathectomy, adrenalectomy produced a rapid and marked fall in blood pressure in both normotensive and hypertensive animals and the blood pressure stabilized around 50 mm Hg within 1 hour after adrenalectomy. Since the basal blood pressure was identical in normotensive and hypertensive animals after removal of both components of the sympathetic system, this suggests that the most likely factor which would account for an elevated blood pressure in rats treated with DOCA and sodium is a synergic hyperactivity of the sympathetic fibers and adrenal medulla.