Peripheral pressor systems in hypertension caused by nucleus tractus solitarius lesions.

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Abstract
The roles of vasopressin, the sympathoadrenal system, and the renin-angiotensin system in the production of hypertension after bilateral destruction of the nucleus tractus solitarius (NTS) were examined in chloralose-anesthetized rats. Since the activity of the renin-angiotensin system is high in anesthetized rats, additional studies were performed in unanesthetized, freely moving rats to evaluate the role of the renin-angiotensin system in hypertension caused by NTS lesions. Hypertension produced by bilateral electrolytic NTS lesions in rats was accompanied by elevated plasma levels of vasopressin (approximately 7-fold), norepinephrine (greater than 10-fold), and epinephrine (greater than 10-fold), but not of plasma renin activity. These results suggest that this form of hypertension is due to increased sympathoadrenal activity and increased vasopressin release into plasma and that the renin-angiotensin system is not involved. In rats with NTS lesions, blockade of vasopressin or the sympathoadrenal system, but not the renin-angiotensin system, elicited an acute decrease in arterial pressure. However, blockade of either vasopressin or the autonomic nervous system before production of the lesions had no effect on the resulting hypertension, indicating that in the absence of either one of these systems bilateral NTS lesions still result in severe hypertension. Although the renin-angiotensin system does not normally contribute to this hypertension, it does appear to contribute to the elevation in blood pressure once the actions of vasopressin have been blocked. In rats pretreated with a vasopressin antagonist, plasma renin activity increased following NTS lesions and the angiotensin converting enzyme inhibitor captopril decreased blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)