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1 University of Adelaide, Department of Medicine, Royal Adelaide Hospital, North Terrace, Adelaide, South Australia, Australia 5000; and 2 St. Louis University Health Center, Division of Geriatric Medicine, St. Louis, Missouri 63104
Animal studies suggest
that nitric oxide (NO) may be a physiological regulator of appetite; NO
synthase (NOS) inhibition suppresses food intake in rats, mice, and
chickens. It is not known whether NO has any effect on appetite in
humans. We have used
NG-monomethyl-L-arginine
(L-NMMA) and
NG-nitro-L-arginine methyl ester
(L-NAME), both competitive,
nonselective inhibitors of NOS, in two separate studies to evaluate the
role of NO in the short-term regulation of appetite in humans. In
study I, 13 men (18-25 yr) underwent
paired studies, in randomized, double-blind fashion, after an overnight
fast. L-NMMA (4 mg · kg
1 · h
1)
or saline (0.9%) was infused intravenously at a rate of 40 ml/h for
1.5 h. In study
II, eight men (18-26 yr)
underwent three randomized, double-blind studies after an overnight
fast. L-NAME (75 or 180 µg · kg
1 · h
1)
or saline (0.9%) was infused intravenously at a rate of 20 ml/h for
120 min. Hunger and fullness were measured using visual analog scales;
blood pressure and heart rate were monitored, and 30 min before the end
of the infusion, subjects were offered a cold buffet meal. Total
caloric intake and the macronutrient composition of the meal were
determined. Both L-NMMA
(P = 0.052) and
L-NAME
(P < 0.05; both doses) decreased
heart rate, L-NMMA increased
diastolic blood pressure (P < 0.01),
and L-NAME increased systolic
blood pressure (P = 0.052). Neither
drug had any effect on caloric intake or sensations of hunger or
fullness. Despite having significant effects on cardiovascular function
in the doses used, neither L-NMMA nor
L-NAME had any effect on
feeding, suggesting that NO does not affect short-term appetite or food
intake in humans.
NG-monomethyl-L-arginine; NG-nitro-L-arginine methyl ester
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