Altered responses of aortic smooth muscle from Sprague-Dawley rats with salt-induced hypertension.

1. The contractile responses of aortic ring preparations from Sprague-Dawley rats made hypertensive by 6-week dietary salt loading were studied. The test and control diet contained 8.0 and 0.3% NaCl, respectively. Aortic rings from salt-loaded rats showed enhanced sensitivity to noradrenaline (NA) but not to serotonin. Contractile responses to CaCl2 in Ca-free NA-containing medium was significantly enhanced in salt-loaded rats, but was unchanged in K(+)-depolarised medium. K(+)-induced relaxation (a functional indicator of Na-K adenosine triphosphatase activity) was sensitive to 10 mumol/L ouabain and was significantly attenuated in aortic rings from salt-loaded rats. The results suggest that hypertension induced by salt-loading is associated with enhanced sensitivity to NA, increased Ca2+ entry through receptor-operated channels, and impairment of Na-K ATPase enzyme activity.