Lack of effect of anti-hypertensive treatment with felodipine on cardiovascular structure of young spontaneously hypertensive rats.

Felodipine (4(2,3-dichlorophenyl)-1,4-dihydro-2, 6-dimethyl-3-ethoxycarbonyl-5-methoxycarbonyl pyridine)), a selective vasodilating anti-hypertensive drug, was used in the treatment of spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto rats (WKYs) from age 6 to 14 weeks, ie during the time of high blood pressure development in SHRs. The effect of treatment on heart weight and on mesenteric resistance vessels (i.d. ca 170 microns) characteristics was investigated. In a first study, two oral doses of felodipine were added to the diet of SHRs, in concentrations of either 0.5 or 1.5 mg X g-1 rat food. Both treatments lowered mean arterial pressure by about 19% (p less than 0.001). In a second study, the lower dose of felodipine (0.5 mg . g-1 rat food) was therefore used to treat both SHRs and WKYs. Treatment did not interfere with weight or food intake of either SHRs or WKYs but increased average weekly water intake significantly. In neither strain was the pulse rate or, surprisingly, heart/body weight ratio affected by treatment. Furthermore, mesenteric resistance vessel morphology and mechanics were not affected by the blood pressure reduction. The noradrenaline and calcium sensitivity of mesenteric resistance vessels from treated rats was greater (p less than 0.001) than those from control rats. These findings indicate that blood pressure reduction with felodipine does not affect cardiovascular structure in young SHRs.