The responses of carotid vascular strips from spontaneously hypertensive and normotensive rats

The responses to noradrenaline (NA) and KCl of carotid arterial strips from spontaneously hypertensive rats (SHR) and three strains of normotensive rats (NR) were compared using tissue obtained from young (5--7 weeks) or older (15--17 weeks) rats. The maximum responses and sensitivity of strips from SHR were less than those of NR in both age groups. Relaxation of maximum NA-induced responses was consistently faster, and relaxation of KCl-induced responses generally slower with strips from SHR. Carotid strips from young SHR showed a greater dependence on extracellular calcium in their responses to NA and a lesser dependence in their KCl-induced responses than tissues from NR. We conclude that the smooth muscle of carotid arteries from SHR differs intrinsically from that of NR and that the differences in vascular responses may be related to altered excitation-contraction processes in the SHR.