Modulation of endothelium-derived nitric oxide in canine femoral veins. Miller, Virginia M., and Dustan A. Barber. Departments of Surgery and Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905
APStracts 3:0061H, 1996.
Experiments were designed to determine whether or not nitric oxide was the mediator of increased endothelium-dependent relaxations in veins proximal to an arteriovenous fistula. A fistula was prepared between femoral arteries and veins in dogs. After six weeks, veins proximal to the fistula were removed, cut into rings and suspended for the measurement of isometric force in organ chambers. In some rings the endothelium was removed deliberately. NG-monomethyl-L-arginine (L -NMMA) caused contraction in three of six fistula-operated veins with and without endothelium. In rings contracted submaximally with prostaglandin F2[alpha], acetylcholine and the alpha2 adrenergic agonist UK 14,304, caused endothelium-dependent concentration -dependent relaxations which were greater in fistula- compared to sham-operated veins. These relaxations were reduced by L-NMMA. Calcium ionophore A23187 caused comparable endothelium-dependent relaxations in fistula- and sham-operated veins which were unaffected by L-NMMA. There were no differences in either calcium-dependent or -independent activity of nitric oxide synthase isolated from fistula- and sham-operated veins. Positive staining for nitric oxide synthase was present in both the endothelium and media of fistula-operated veins. These results indicate that nitric oxide mediates increased endothelium-dependent relaxations to acetylcholine and alpha2 -adrenergic agonists in fistula-operated veins. Therefore, chronic increases in blood flow and oxygen tension modify selectively receptor-coupled production of nitric oxide in endothelium and smooth muscle of veins. 

Received 15 April 1994; accepted in final form 13 December 1995.
APS Manuscript Number H339-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96