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Am J Physiol Regul Integr Comp Physiol 281: R98-R107, 2001;
0363-6119/01 $5.00
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Vol. 281, Issue 1, R98-R107, July 2001

Activation of alpha 2-receptors in the rostral ventrolateral medulla evokes natriuresis by a renal nerve mechanism

Rubia Grecco Menegaz1, Daniel R. Kapusta2, Helder Mauad1, and Antonio de Melo Cabral1

1 Department of Physiological Sciences, Medical Center Federal University of Espirito Santo, Vitoria, Brazil 29040 - 090; and 2 Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112

The contribution of alpha 2-receptor mechanisms in the rostral ventrolateral medulla (RVLM) in mediating the enhanced renal excretory responses evoked by the intravenous infusion of the alpha 2-receptor agonist xylazine was examined in ketamine-anesthetized rats. In ketamine-anesthetized rats, the bilateral microinjection of the alpha 2-receptor antagonist yohimbine into the RVLM significantly reduced the enhanced levels of urine flow rate (V) and urinary sodium excretion (UNaV) produced by xylazine. In contrast, microinjection of yohimbine into the RVLM of chronically bilaterally renal-denervated rats significantly reduced the xylazine-evoked diuretic, but not natriuretic, response. In separate ketamine-anesthetized rats, intravenous xylazine infusion produced a near complete inhibition of renal sympathetic nerve activity (RSNA). The subsequent microinjection of yohimbine into the RVLM reversed this neural response and concurrently decreased V and UNaV. Together, these results indicate that during intravenous infusion, xylazine activates alpha 2-receptor mechanisms in the RVLM to selectively promote urinary sodium excretion by a renal nerve-dependent pathway. In contrast, activation of alpha 2-receptor in the RVLM affects the renal handling of water by a pathway independent of the renal nerves. This latter pathway may involve an interaction with other brain regions involved in antidiuretic hormone release (e.g., paraventricular nucleus of the hypothalamus).

renal sympathetic nerves; renal excretory function; urine flow rate; urinary sodium excretion; central nervous system; microinjection


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