Preoptic hypothalamic lesions reduce adrenergic vascular compensation during hemorrhagic shock.

The effect of electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V-X) of the rat brain on vascular compensation during prolonged hypotensive hemorrhage was determined. Anesthetized AV3V-X and control-operated (Cont) animals were subjected to a modified Wigger's hemorrhagic shock protocol. Maximum bled volume (MBV) was significantly lower in AV3V-X rats (2.74 +/- 0.14 ml/100 g BW) compared with control animals (3.51 +/- 0.16 ml/100 g BW). Pretreatment with the nonspecific alpha-adrenergic antagonist phentolamine (2.74 +/- 0.16 ml/100 g BW) or with the alpha 1-adrenergic antagonist prazosin (2.85 +/- 0.17 ml/100 g BW) reduced MBV in Cont rats, but did not attenuate MBV in AV3V-X animals (phentolamine: 2.33 +/- 0.17 ml/100 g BW; prazosin: 2.4 +/- 0.2 ml/100 g BW). In addition, maximum vasoconstriction was maintained for a significantly shorter period of time in AV3V-X (11.8 +/- 2.5 min) compared with Cont (30.8 +/- 10.5 min). These findings suggest that AV3V-X results in a deficit of alpha 1-adrenoreceptor activation during prolonged hypotension.