THE INFLUENCE OF 17-BETA-ESTRADIOL AND THE NATURAL ESTROUS-CYCLE ON ALPHA-ADRENOCEPTOR-MEDIATED RESPONSES OF THE CARDIOVASCULAR-SYSTEM IN THE RAT

The effect of 17 beta-oestradiol pretreatment and the natural oestrous cycle on responses of rat cardiac and vascular alpha-adrenoceptors was investigated. It was found that treatment with the oestrogen had no effect on cardiac adrenoceptor sensitivity, while pretreatment with the hormone caused a significant increase in vascular alpha(2)(-), but not vascular alpha(1)-adrenoceptor responsiveness. Presser responses of pithed rats to selective alpha(1)- or alpha(2)-adrenoceptor agonists did not alter, however, during the natural oestrous cycle. These findings suggest that changes in oestrogen levels are capable of altering alpha-adrenoceptor-mediated vascular responses but that the relatively small changes in oestrogen which may occur throughout the natural oestrous cycle do not appear to alter the responses of these vascular alpha-adrenoceptors.