Role of vascular alpha 2-adrenoceptors as targets for circulating catecholamines in the maintenance of blood pressure in anaesthetised spontaneously hypertensive rats.

We examined the blood pressure-lowering effects of the alpha 2-adrenoceptor antagonist rauwolscine in anaesthetised spontaneously hypertensive rats (SHR). In the absence of prior drug, rauwolscine (1-10 mg kg-1) produced dose-dependent falls in diastolic blood pressure (DBP). In the presence of prazosin (1 mg kg-1) to eliminate alpha 1-adrenoceptor-mediated responses, rauwolscine (0.1-1 mg kg-1) lowered DBP in unoperated and sham-operated animals but not in adrenal demedullated animals. Hence, we were able to demonstrate that alpha 2-adrenoceptors are involved in the control of blood pressure in intact anaesthetised SHR but not following adrenal demedullation, suggesting that circulating catecholamines are responsible for these alpha 2-adrenoceptor-mediated pressor effects.