Responses to noradrenaline of portal vein strips from normotensive and spontaneously hypertensive rats.

1 Responses to noradrenaline of isolated portal vein strips from 5-7 week and 15-17 week Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) have been examined. 2 15-17 week SHR tissue exhibited a greater sensitivity (lower ED50) to noradrenaline but only at reduced Ca2+EXT levels. 3 pA2 values for the alpha-adrenoreceptor antagonists WB 4101 and prazosin were significantly lower in 5-7 week SHR consistent with some change at the adrenoreceptor level. 4 Veins from SHR relaxed more rapidly in CA2+-free saline following removal of noradrenaline than did veins from WKY. 6 D600 is a competitive antagonist of the Ca2+EXT-dependent component of the noradrenaline response but K1 values were not significantly different in SHR and WKY.