Intravenous β-endorphin administration fails to alter hypothalamic blood flow in rats expressing normal or reduced nihic oxide synthase activity

-Endorphin (β-END) significantly contributes to the maintenance of hypothalamic blood flow (HBF) autoregulation during hemorrhagic hypotension in rats. Recently, several natural and synthetic opioid peptides were reported to induce nitric oxide (NO)-mediated dilation in the cerebrovascular bed. In the present study, the effect of β-END was studied on HBF and hypothalamic vascular resistance (HVR) in vehicle-treated control rats and in rats after the pharmacological inhibition of the NO synthesis by chronic oral application of N(G)-nitro-L-arginine methyl ester. Intravenous β-END administration faired to alter HBF or HVR either in control or in NO-blocked animals, and its transient hypotensive effect was not inhibited by NO blockade, indicating that β-END may not have NO-mediated vasodilator effect in the hypothalamic or in the systemic circulation.