Journal of Applied Physiology
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J Appl Physiol 77: 2291-2298, 1994;
8750-7587/94 $5.00
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Journal of Applied Physiology, Vol 77, Issue 5 2291-2298, Copyright © 1994 by American Physiological Society

ARTICLES

Systemic hemorrhage augments local O2 extraction in canine intestine

R. W. Samsel and P. T. Schumacker
Pulmonary and Critical Care Medicine, University of Chicago, Illinois 60637.

When O2 delivery (QO2) to a tissue is reduced, microvascular adjustments facilitate increases in O2 extraction, thereby delaying the onset of O2 supply-limited metabolism until a critically low QO2 is reached. The present study investigated the contribution of the autonomic nervous system to these adjustments by measuring O2 extraction in isolated intestine. In anesthetized dogs, a 30- to 50-g segment of intestine was vascularly isolated and its QO2 was decreased in stages by reducing the speed of an occlusive pump. In a normovolemic group (n = 11), blood volume was maintained to minimize sympathetic tone while flow to the intestine was reduced. In a hypovolemic group (n = 7), blood volume was removed in stages to augment sympathetic tone as flow to the intestinal segment was simultaneously reduced. A hypovolemic alpha-adrenergic-blocked (alpha-blocked) group (n = 6) was identical to the corresponding alpha-adrenergic intact (alpha-intact) group except that alpha-adrenergic effects were inhibited with phenoxybenzamine (3 mg/kg). The systemic critical O2 extraction ratio in the alpha-blocked group (69 +/- 6%) was less than that in the alpha-intact group (77 +/- 7%; P = 0.05). In the intestine, the critical O2 extraction ratio was significantly poorer in the normovolemic (45 +/- 11%) group than in either hypovolemic group (alpha-intact: 69 +/- 3%, P < 0.00005; alpha-blocked: 62 +/- 9%, P < 0.005). These findings demonstrate that systemic hemorrhage significantly augments critical O2 extraction in intestine during progressive local stagnant hypoxia and suggest that nonadrenergic vasoconstrictor mechanisms may play an important role.


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