Impaired arginine metabolism and nitric oxide synthesis in coronary
endothelial cells of the spontaneously diabetic bb rat.
Wu, Guoyao, and Cynthia J. Meininger.
Departments of Animal Science and Medical Physiology, Texas A&M
University, College Station, Texas, U.S.A. 77843
APStracts 2:0140H, 1995.
Arginine metabolism via nitric oxide (NO) synthase and other pathways
was studied in coronary endothelial cells (EC) from the spontaneously
diabetic BB rat, an animal model of human Type I diabetes mellitus
(IDDM). EC were prepared from insulin-treated diabetic BB (BBd) and
non-diabetes prone BB (BBn) rats. Basal NO synthesis was studied in
EC cultured for 48 h in medium containing 0.4 mM L-arginine. At the
end of the culture period, the medium was analyzed for nitrite and
nitrate (two major end stable oxidation products of NO), and the
cells were used to determine arginine uptake and metabolism and the
activities of some arginine-degrading enzymes. For studies of
arginine metabolism, cells were incubated at 37oC for 1 h in Krebs
-Henseleit bicarbonate buffer (pH 7.4) containing 1 mM L-[1
-14C]arginine or L-[1-14C]ornithine. The rates of production of
nitrite plus nitrate by BBd EC were only 15% of those of BBn cells.
This impaired NO synthesis in BBd EC was not due to alterations in
arginine uptake, NO synthase activity, or intracellular arginine
concentrations, but might have resulted from a limited intracellular
availability of co-factors of NO synthase. In addition to the
arginine-NO pathway, arginine was found to be metabolized to urea,
ornithine and, to a much lesser extent, CO2 via arginase and
ornithine aminotransferase. The activities of arginase and the
formation of ornithine and urea from arginine were decreased by 90%
in BBd compared with BBn cells. These results, coupled with the
reduced NO synthesis, indicate metabolic defects in arginine
metabolism in BBd EC. We suggest that arginine degradation in
coronary EC occurs predominantly via the arginase pathway. Our
findings may offer a biochemical basis for the hitherto unexplained
observations that endothelium-dependent relaxation is impaired in BBd
rats and IDDM patients.
Received 2 December 1994; accepted in final form 5 April 1995.
APS Manuscript Number H1057-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.