DELAYED DEVELOPMENT OF HYPERTENSION AFTER SHORT-TERM NITRENDIPINE TREATMENT

In this study we evaluated the delayed effects of a calcium entry bloc ker on blood pressure and on vascular structural and functional altera tions in mesenteric resistance arteries of spontaneously hypertensive rats (SHR). The calcium entry blocker nitrendipine was administered (3 0 mg/kg per day) according to three different schedules: in one group of SHR from 4 to 8 weeks of age (n=12), in a second group from 8 to 12 weeks of age (n=12), and in a third group from 4 to 12 weeks of age ( n=12). Twelve untreated SHR and 12 untreated Wistar-Kyoto rats served as controls. Half the animals of each group were killed at 13 weeks, a nd the remaining were killed at 38 weeks. After death, relative left v entricular mass was calculated. Vascular morphology and function (resp onses to norepinephrine and acetylcholine) in mesenteric small arterie s were then assessed using a micro-myographic technique. Nitrendipine treatment delayed the development of hypertension and determined the r egression of structural alterations of mesenteric resistance arteries in SHR. These favorable effects were maintained for several weeks afte r treatment withdrawal, provided that treatment was started at 4 weeks of age. Considering the functional alterations of mesenteric arteries in SHR (responses to norepinephrine and acetylcholine), nitrendipine treatment determined an improvement of both these dysfunctions as long as reductions of the media-to-lumen ratio and blood pressure, respect ively, were maintained.