INFLUENCE OF ALPHA-1-ADRENOCEPTOR AND ALPHA-2-ADRENOCEPTOR ANTAGONISTTHERAPY ON THE DEVELOPMENT OF HYPERTENSION IN SPONTANEOUSLY HYPERTENSIVE RATS

There is general agreement that the sympathetic nervous system is invo lved in the development of hypertension in spontaneously hypertensive rats (SHR). However, in a previous study we established that chronic a dministration of the selective alpha1-adrenoceptor antagonist terazosi n to SHR failed to prevent this phenomenon. In the present study, we e xtended that investigation further by examining the effects of another selective alpha1-antagonist (doxazosin), an alpha2-adrenoceptor antag onist (yohimbine), and a combination of these agents. Chronic administ ration of doxazosin and yohimbine produced receptor blockade, as deter mined by their effect on blood pressure (BP) responses to norepinephri ne (NE) and phenylephrine. Chronic administration of either antagonist alone or the two in combination failed to prevent the development of hypertension in SHR, however. These findings suggest that although the re may be a need for involvement of the sympathetic nervous system in the development of hypertension in SHR, its influence on this process is not mediated through activation of alpha-adrenoceptors.