Regulation of arterial adrenoceptors during hypertension development in spontaneously hypertensive rats

Diminished beta-adrenoceptor mediated relaxation and increased reactivity to norepinephrine have been observed in the arteries of spontaneously hypertensive rats (SHR). However, some reports are conflicting, while the complexity of endothelial, neural and purely morphological factors regulating the response of whole vessels is increasingly appreciated. Thus a dissection of the complex vascular contraction mechanism into single-step events is needed. Here characterization of adrenoceptors in isolated aortic smooth muscle cells of SHR by radioligand binding techniques is reported. The density of beta-adrenoceptors was decreased at 4 (-23%), 7(-20%) and 13(-39%) weeks in SHR compared with age-matched normotensive Wistar-Kyoto rats. In both strains beta-adrenoceptor density decreased significantly with age. alpha 1-Adrenoceptors exhibited complex, though slight, changes in SHR at different ages. The alpha/beta adrenoceptor density ratio was constantly increased in SHR (11.9 versus 7.6 at 7 weeks; 19.1 versus 15.8 at 13 weeks). These findings suggest that the abnormal contractility of SHR arteries may at least partially depend on changes at the adrenoceptor level. A loss of arterial beta-adrenoceptors early in the life of SHR can be an event leading to increased peripheral resistance and elevation of blood pressure.