Effect ofβ-adrenoceptor agonists on vascular smooth muscle contraction and transmitter release in portal vein from spontaneously hypertensive rats

The effect ofβ-adrenoceptor agonists on vascular smooth muscle contractile tension and transmitter release of portal vein from the spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) was investigated. As compared with the normotensive WKY portal vein, the sensitivity of SHR’s portal vein to relaxing effect of isoprenaline (Iso) and terbutaline (Ter) was significantly decreased. Whereas dobutamine (Dob) only showed slightly but the same inhibitory tendency on the contractile reaction by field-stimulation in portal vein from these two kinds of rats. So the portal vein postsynaptic receptor activity was decreased in SHR. All of theseβ-adrenoceptor agonists used showed facilitory effect on the evoked transmitter release of sympathetic terminal in the portal vein. But Iso lμmol/L slightly decreased in evoked [3H]NE release from SHR portal vein. There was no significant difference between the reactions of portal vein from these two kinds of rats. These results suggest that both subtypes ofβ1 andβ2-receptors may be present on the presynaptic nerve terminals, and the sensitivity of presynapticβ-receptors may not necessarily be raised in hypertension.