AJP - Gastrointestinal and Liver Physiology, Vol 271, Issue 3 400-G404, Copyright © 1996 by American Physiological Society

ARTICLES

Autoregulatory capacity in the superior mesenteric artery is attenuated by nitric oxide

M. P. Macedo and W. W. Lautt
Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.

The hypothesis that nitric oxide antagonizes pressure-flow autoregulation in the superior mesenteric artery was tested with the use of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and L-arginine. Autoregulation was assessed with the use of two indexes: 1) the autoregulatory index (ARI), expressed as the ratio of change in flow to change in pressure tested over the nonautoregulatory range, 40-70 mmHg, and over the autoregulatory range, 70-140 mmHg; and 2) the slope index, an index of linearity of the pressure-flow curve calculated by dividing the slope of the pressure-flow curve over the autoregulatory range by the slope of the curve over the nonautoregulatory range, expressed as percent. L-NAME significantly increased autoregulation from an ARI of 0.06 +/- 0.05 to 0.28 +/- 0.09 over the autoregulatory range (P < 0.003), and the nitric oxide synthase substrate L-arginine reversed ARI to 0.12 +/- 0.07 (mean +/- SE, n = 7). ARI in the nonautoregulatory range was not altered. The slope index revealed that L-NAME enhanced autoregulation (61 +/- 5.6 compared with control, 93.4 +/- 7.9; P < 0.003), which was reversed by the action of L-arginine (88.5 +/- 5.5, P < 0.007). The data were consistent with the hypothesis that increased flow leads to nitric oxide-induced dilation, which counteracts autoregulation.

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