Objectives: The aim of this study was to determine whether the acute inhibi
tion of nitric oxide (NO) synthase causes changes in cardiac substrate util
ization which can be reversed by a NO donor. Methods: NO synthase was block
ed by giving 30 mg/kg of nitro-L-arginine (NLA) i.v. to 15 chronically inst
rumented dogs. Hemodynamics and blood samples from aorta and coronary sinus
were taken at control and at 1 and 2 h after NLA. In five dogs, 0.4 mg/kg
of the NO donor 3754 was given i.v. 1 h after NLA. In six dogs, angiotensin
II was infused over 2 h (20-40 ng/kg/min) to mimic the hemodynamic effects
of NLA. Results: Two h after NLA: mean arterial pressure was 153+/-4 mmHg;
MVO2 increased by 38%; cardiac uptake of lactate and glucose increased, re
spectively, from 20.0+/-5.0 to 41.0+/-9.3 mu mol/min and from 1.1+/-0.7 to
6.8+/-1.5 mg/min (all P<0.05 vs. control). Cardiac uptake of free fatty aci
ds decreased by 43% after 1 h (P<0.05) and returned to control values at 2
h. Cardiac respiratory quotient increased from 0.76+/-0.03 to 1.05+/-0.07,
indicating a shift to carbohydrate oxidation. All these changes were revers
ed by the NO donor. In the dogs receiving angiotensin II infusion, MVO2 inc
reased by 28% and lactate uptake doubled (both P<0.05), but no other metabo
lic changes where observed. Conclusions: The acute inhibition of NO synthas
e by NLA causes a switch from fatty acids to lactate and glucose utilizatio
n by the heart which can be reversed by a NO donor, suggesting an important
regulatory action of NO on cardiac metabolism. (C) 1999 Published by Elsev
ier Science B.V. All rights reserved.