Microsphere analysis of β2-adrenergic control of resistance in different vascular areas after hemorrhage

In cats exposed to bleeding (exsanguination of 15 ml×kg bwt^-1) the microsphere technique was used to determine regional vascular resistances in a large number of tissues before and after i.v. administration of the ‘selective’β₂-adrenoceptor antagonist ICI 118,551. β₂-blockade significantly raised vascular resistance in the stomach (+26%), small (+25%) and large (+38%) intestine, pancreas (+29%), kidney (+39%), omental (+33%) and subcutaneous (+26%) fat, ‘white’ skeletal muscle (+19%), and skin (+24%). These findings indicate that, with intact β-adrenoceptors, β₂-adrenergic dilator interaction counteracted the hemorrhage evoked vasoconstrictor influences. β₂-blockade also evoked quite a strong increase of total peripheral resistance (19%) and led to some redistribution of cardiac output. It is concluded that β₂-adrenergic inhibition of vascular tone significantly seems to improve tissue perfusion during bleeding in several vascular areas. Such effects may be of special significance during severe hemorrhage. In the intestine, pancreas, and adipose tissue, for example, protection against excessive vasoconstriction may serve to minimize the severe metabolic disturbances with secondary release of toxic factors into the circulation reported during hemorrhagic shock.