(Hypertension. 1995;25:828-833.)
© 1995 American Heart Association, Inc.
Articles |
Acute Hypertension Increases Norepinephrine Release in the Anterior Hypothalamic Area
From the Department of Cell Biology (N.P., K.K., J.M.W.) and the Vascular Biology and Hypertension Program of the Department of Medicine (Q.C.M., S.O., J.M.W.), University of Alabama at Birmingham.
Correspondence to J. Michael Wyss, PhD, Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294-0019.
Abstract Neurons in the anterior hypothalamic area play an important role in NaCl-sensitive hypertension in spontaneously hypertensive rats, and previous studies have suggested that baroreceptor feedback modifies the activity of these neurons. To test the hypothesis that the release of norepinephrine in the anterior hypothalamic area is modified by arterial baroreceptor reflex feedback and that this reflex release is disturbed in spontaneously hypertensive rats on a high NaCl diet, we used the push-pull technique to measure the release of the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylglycol in the anterior hypothalamic area. Seven-week-old male spontaneously hypertensive and normotensive Wistar-Kyoto rats were placed on a high (8%) or a basal (1%) NaCl diet for 2 weeks. The high NaCl diet elevated mean arterial pressure and greatly reduced basal norepinephrine metabolite levels in the anterior hypothalamic area of the spontaneously hypertensive (but not the control) rats (305±32 pg/10 min in the rats consuming 1% NaCl and 93±9 pg/10 min in the rats consuming 8% NaCl). An infusion of tramazoline (an imidizoline that causes long-lasting hypertension) that increased arterial pressure by 25 mm Hg elevated anterior hypothalamic area norepinephrine metabolite concentrations significantly more in the spontaneously hypertensive rats on the 1% NaCl diet (to 392±46 pg/10 min) than in those on the 8% NaCl diet (to 113±18 pg/10 min). In contrast, in Wistar-Kyoto rats the tramazoline-induced increase in arterial pressure elevated anterior hypothalamic area norepinephrine metabolite concentrations slightly more in rats on the 8% NaCl diet than in those on the 1% NaCl diet. These data suggest that baroreflex activation increases norepinephrine release in the anterior hypothalamic area of the awake rat and that a high NaCl diet blunts this response in spontaneously hypertensive (but not Wistar-Kyoto) rats.
Key Words: sympathetic nervous system • rats, inbred WKY • hypertension, sodium-sensitive • hypothalamus • sodium
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