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     CENTRAL HYPOTENSIVE ACTION OF CLONIDINE
              REQUIRES NITRIC OXIDE
     L.W. Dobrucki1 C.L. Cabrera2 D.F. Bohr2 T. Malinski1
1=Ohio University, Athens, OH, USA 2=Univ. Of Michigan, Ann Arbor, MI, USA   10=

Because nitric oxide (NO) acting in the brain lowers blood pressure, we
determined whether central antihypertensive action of clonidine was
mediated by its stimulation of NO release. Porphyrinic sensors were used
to quantify NO concentration in the nucleus tractus solitarious (NTS) in
vitro in brain slices,and in vivo in the anesthetized rat. In both preparations
the unstimulated concentration of NO was approximately 15 nm/L.
Clonidine increased this value to 87 in vitro and to 128 in vivo where it was
infused ICV This ICV infusion lowered MAP 22 mmHg. Blockade of NO
release with L-NAME reduced this response to 3 mmHg. We conclude that
stimulation of the release of NO by clonidine contributes to its central
antihypertensive                                                        action.




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