Calcium reactivity and antagonism in portal veins from spontaneously hypertensive and normotensive rats

Reactivities of portal veins from spontaneously hypertensive rats (SHR) and normotensive controls (Wistar Kyoto, WKY) at 5-7 and 15-17 weeks of age were compared. Systolic blood pressures were not different at 5-7 weeks but those of SHR were significantly elevated (177 ± 4 mmHG) (1 mmHg = 133.322 Pa) at 15-17 weeks. Spontaneous activity, frequency, and tension were greater in SHR for both age groups. Young SHR were more sensitive to K⁺ at 5-7 weeks but less sensitive at 15-17 weeks than age-matched WKY rats. Sensitivity to Ca²⁺ in a K⁺-depolarizing medium was higher in SHR than in WKY for both age groups. Maximum tension responses to K⁺ or Ca²⁺ were greater in SHR. The Ca²⁺ channel antagonists nifedipine, nitrendipine, and nisoldipine were potent inhibitors of both noradrenaline- and K⁺-induced responses but did not show differences in inhibitory activity between WKY and SHR.