Effects of alpha-adrenergic blockade on coronary blood flow of dogs in hemorrhagic shock.

The present study was designed to test the hypothesis that the vasoconstrictive effects of alpha-adrenergic receptors are responsible, at least in part, for the lack of a maximal vasodilatation of coronary arteries during hemorrhagic shock. Open-chested, anesthetized, mongrel dogs were bled so as to reach an arterial pressure level of 44 mm Hg, and were monitored using an electromagnetic, non-cannulating flowmeter. During shock, two intracoronary injections were made, one of saline, the other of phenoxybenzamine (Dibenzyline). Control dogs had 2 injections of saline. Following phenoxybenzamine, coronary blood flow increased by 32%. These results indicate that although coronary blood flow may be mainly under local control, the sympathetic nervous system limits maximal coronary vasodilatation during hemorrhagic shock by virtue of activated alpha-adrenergic receptors.