Inositol phosphate formation and contractile response linked to alpha 1-adrenoceptor in tail artery and aorta from spontaneously hypertensive and Wistar-Kyoto rats.

The relation between norepinephrine (NE)-induced contraction and inositol phosphate (IP) formation was investigated in aorta and tail artery rings from adult spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Norepinephrine (NE) contracted the tail artery of WKY and SHR with similar potency (-log EC50 6.6 +/- 0.1 and 6.5 +/- 0.08, respectively), but the maximum tension developed by SHR (0.98 +/- 0.03 g weight) was greater as compared with WKY (0.75 +/- 0.09 g weight). [3H]IP accumulation in the NE-stimulated tail artery was enhanced (p < 0.05-0.01) in SHR as compared with WKY, the potency exhibited being similar in both groups of rats. In aortic rings, in contrast, sensitivity to NE was reduced in SHR as compared with WKY rats (-log EC50 7.92 +/- 0.16 and 8.44 +/- 0.14, respectively) whereas the maximum developed tension was similar. There was also a nonsignificant trend for [3H]IP formation to be impaired in SHR as compared with WKY. Furthermore, results obtained in Ca(2+)-free medium appears to indicate that the contribution of intracellular calcium to NE-induced contraction is greater in tail artery than in aorta. Together, these data suggest that differences in alpha 1-adrenoceptor-mediated contraction observed between blood vessels of SHR and WKY are associated with qualitatively similar alterations in the [3H]IP accumulation linked to alpha 1-adrenoceptor stimulation.