The role of the adrenal medulla in neural control of blood pressure in rats.

The role of the adrenal medulla in the regulation of blood pressure was assessed in rats. In conscious intact (SHAM) and adrenal demedullated (DEMED) animals, baseline blood pressures and heart rates were not different. Moreover, equivalent pressor and depressor response curves to norepinephrine and sodium nitroprusside were obtained. Plasma concentration and 24 hr urinary excretion of norepinephrine were not altered by demedullation. However, epinephrine was undetectable in the urine of the DEMED rats. The effectiveness of the demedullation was further evidenced by a greater than 99% decrease in the epinephrine and norepinephrine content of the adrenal glands of DEMED animals. In pithed SHAM rats, electrical stimulation of preganglionic sympathetic neurons (.5 to 16 hz) elicited marked increases in plasma epinephrine indicating adrenal stimulation, whereas in DEMED rats there were no increases. Furthermore, increments in plasma norepinephrine were significantly reduced in DEMED rats, yet the blood pressure increases were greater than in SHAM rats. Thus, adrenal catecholamine release did not contribute to the blood pressure responses, but in fact, may have had an opposite action due to the vasodilatory actions of epinephrine. The results demonstrate that the adrenal medulla is not essential for reflex compensation to a hypotensive challenge or to the blood pressure increases produced to direct neural stimulation.