CLONIDINE HYPOTENSION IN SPONTANEOUSLY HYPERTENSIVE RATS (SHR) DEPENDS ON THE FUNCTIONAL-STATE OF GABAERGIC AND GLUTAMATERGIC SYSTEMS

The effect of gamma-aminobutyric acid (GABA)(A) receptors and of the N -methyl-D-aspartate (NMDA) subtype of glutamate receptor blockade on c lonidine hypotension was studied. The experiments were performed on sp ontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY), ra ts. We found that the blockade of GABA(A) receptors by bicuculline sig nificantly (P < 0.01) reduced hypotensive responses to clonidine. Simi larly, the NMDA receptor antagonist dizocilpine (MK-801) completely ab olished the blood pressure lowering effect of clonidine. Our findings support the conclusion that clonidine hypotension is closely related t o the functional state of both inhibitory GABAergic and excitatory glu tamatergic systems.