Effect of felodipine on resistance vessels from spontaneously hypertensive and normotensive rats.

We have investigated the effect of felodipine [4-(2,3,-dichlorophenyl)-1,4-dihydro-2, 6-dimethyl-3-ethoxycarbonyl-5-ethoxycarbonylpyridine] on the calcium concentration response relations of noradrenaline-activated mesenteric resistance vessels from 3-mo-old spontaneously hypertensive (SHR) and age-matched Wistar-Kyoto (WKY) rats. SHR vessels were more sensitive to calcium (ED50 approximately equal to 5.49 X 10(-5) M) than WKY vessels (ED50 approximately equal to 1.01 X 10(-4) M) in control condition. Also, maximal active tension development in SHR vessels was greater (3.14 N/m) than in WKY vessels (2.22 N/m). Felodipine (10(-12) M) decreased calcium sensitivity in vessels from both strains and also decreased maximal active tension development of SHR vessels. In a higher concentration (5 X 10(-10) M), the calcium sensitivity of both SHR and WKY vessels became similar. The active tension development was equally reduced in both rat strains. The results indicate that at least part of the antihypertensive effect of felodipine is due to a direct vasodilation, and also that vessels from SHRs may be more sensitive to felodipine than those from WKY rats.