REACTIVITY AND SENSITIVITY OF THE MESENTERIC-ARTERY IN ADULT SPONTANEOUSLY HYPERTENSIVE RATS AFTER CHRONIC TREATMENT WITH INDAPAMIDE

The effects of chronic treatment with indapamide (3 mg/kg/day) on the structure and function of the mesenteric artery were studied in two gr oups of spontaneously hypertensive rats (SHRs) using an experimental m odel of in situ localized mesenteric artery. Indapamide (n = 12) or pl acebo (n = 12) were given to 8-week-old rats for 4 weeks. After anesth esia and laparotomy, a segment of mesenteric artery (external diameter , 300-400 mum) was exposed for video-microscopic measurements. The dia meter-pressure relationships were established under active conditions (phenylephrine, 10(-6) M) and passive conditions (potassium cynanide, KCN) for transmural pressure ranging from atmospheric pressure to 200 mm Hg. These studied arterial segments were then fixed and their wall cross-sectional areas (CSA) measured in transverse sections. Active wa ll stress and tension were defined as the differences in wall stresses and wall tensions calculated for active and passive conditions. Systo lic arterial pressure and mesenteric CSA were decreased in treated rat s (197 +/- 15 mm Hg vs. 211 +/- 12 mm Hg, p < 0.05; 16,230 +/- 1048 mu m2 vs. 19,033 +/- 1082 mum2, p < 0.05). In both groups, mesenteric dia meters were smaller under active than under passive conditions without significant differences in treated vs. untreated group under active c onditions. The active wall tension was lower in treated (0.4 +/- 0.19 N/m) than in untreated rats (1.19 +/- 0.62 N/m, p < 0.05). However, th ere were no differences in active wall stress in both groups (103 +/- 47 kPa and 134 +/- 30 kPa). These results suggest that chronic treatme nt with indapamide induced a reduction of the mesenteric arterial smoo th-muscle mass associated with a marked decrease in its maximal contra ctile tone. The latter was related to the smooth-muscle mass reduction and not to alteration of the vascular muscle contractility.