Antihypertensive and hypothalamic depressant effects of tripamide in spontaneously hypertensive rats

When tripamide was added to the food of spontaneously hypertensive rats (SHR), there were no appreciable effects on heart rate, body weight, or food intake. Tail-cuff systolic pressures measured weekly were also unaffected in normotensive control rats (WKY), but the elevation expected in SHR was significantly reduced. Pressor responses to hypothalamic stimulation were also reduced selectively only in SHR. A peripheral inhibition of cardiovascular reactivity was considered unlikely, since pressor responses to injected norepinephrine, tyramine, or vasopressin were unaltered. Diminished pressor responsiveness was considered to be due to concurrent reduction of central sympathetic vasomotor activity, because sympathetic nerve responses to hypothalamic stimulation were appreciably lessened in tripamide-treated SHR. Although neither the site nor the mechanism causing sympathetic inhibition was determined exactly, our results are in accord with the interpretation that antihypertensive effects of tripamide in SHR depend, at least partly, on sympathetic inhibition.