The blood pressure effects of alpha-adrenoceptor antagonists injected in the medullary site of action of clonidine: the nucleus reticularis lateralis.

We administered a series of alpha-blocking drugs to the nucleus reticularis lateralis (NRL) of the medulla oblongata, the main site for the hypotensive action of clonidine. These experiments were performed on pentobarbital anaesthetized cats. Drugs were injected through a needle which was stereotaxically inserted. Prazosin (6 nmol) was hypertensive (MBP = +25 +/- 8%), corynanthine had no effect and AR-C239 (7 nmol), another alpha 1-blocker, was hypotensive (MBP = -16 +/- 3.5%). The alpha 2-blockers, yohimbine and idaxozan, were hypotensive. The blood pressure effects of alpha-blocking drugs directly microinjected in the nucleus reticularis lateralis cannot be simply related to their selectivity for a particular subtype of alpha-receptors.