Possible role of central alpha 1-adrenoceptors in the control of the autonomic nervous system in normotensive and spontaneously hypertensive rats.

The cardiovascular effects of AR-C 239, a new and selective alpha 1-adrenoceptor blocking drug were studied in normotensive and spontaneously hypertensive rats (SHR). AR-C 239 (300 micrograms/kg i.v.) did not change the heart rate in control (without pretreatment) and bilaterally vagotomized normotensive rats, but induced significant bradycardia in rats pretreated with a beta-adrenoceptor blocking drug. This bradycardic effect was inhibited by atropine or bilateral vagotomy. In SHR, the administration of AR-C 239 reduced heart rate in the control, bilaterally vagotomized and beta-blocked rats. Blood pressure was decreased in the same way in the two rat strains. It is suggested that central alpha 1-adrenoceptors could participate in the control of vagal tone in normotensive and SH rats, and of sympathetic activity in the SHR only.