OxyFile #223

The inhibitory effect of 3-amino-1,2,4-triazole on relaxation 
induced by hydroxylamine and sodium azide but not hydrogen 
peroxide or glyceryl trinitrate in rat aorta.


Author:   Mian KB; Martin W

Source:   Br J Pharmacol 1995 Dec; 116(8):3302-8

Abstract:

1. In this study we investigated the role of catalase in 
relaxation induced by hydroxylamine, sodium azide, glyceryl 
trinitrate and hydrogen peroxide in isolated rings of rat 
aorta. 2. Hydrogen peroxide (1 microM-1 mM)-induced concentration-
dependent relaxation of phenylephrine (PE)-induced tone in 
endothelium-containing rings. In endothelium-denuded rings, 
however, higher concentrations (30 microM-1 mM) of hydrogen 
peroxide were required to produce relaxation. The endothelium-
dependent component of hydrogen peroxide-induced relaxation was 
abolished following pretreatment with N(O)-nitro-L-arginine methyl 
ester (L-NAME, 30 microM). L-NAME (30 microM) had no effect, 
however, on hydrogen peroxide-induced relaxation in endothelium-
denuded rings. 3. Pretreatment of endothelium-denuded rings with 
catalase (1000 u ml-1) blocked relaxation induced by hydrogen 
peroxide (10 microM-1 mM). The ability of catalase to inhibit 
hydrogen peroxide-induced relaxation was partially blocked 
following incubation with 3-amino-1,2, 4-triazole (AT, 
50 mM) for 30 min and completely blocked at 90 min. 4. 
Pretreatment of endothelium-denuded rings with methylene 
blue (MeB, 30 microM) inhibited relaxation induced by hydrogen 
peroxide (10 microM-1 mM), sodium azide (1-300 nM), hydroxylamine 
(1-300 nM) and glyceryl trinitrate (1-100 nM) suggesting 
that each acted by stimulation of soluble guanylate cyclase. 
5. Pretreatment of endothelium-denuded rings with AT (1-50 
mM, 90 min) to inhibit endogenous catalase blocked relaxation 
induced by sodium azide (1-300 nM) and hydroxylamine (1-300 
nM) but had no effect on relaxation induced by hydrogen 
peroxide (10 microM-1 mM) or glyceryl trinitrate (1-100 
nM). 6. In a cell-free system, incubation of sodium azide 
(10 microM-3 mM) and hydroxylamine (10 microM-30 mM) but 
not glyceryl trinitrate (10 microM-1 mM) with catalase 
(1000 u ml-1) in the presence of hydrogen peroxide (1 mM) 
led to production of nitrite, a major breakdown product 
of nitric oxide. AT (1-100 mM) inhibited, in a concentration-
dependent manner, the formation of nitrite from azide in the 
presence of hydrogen peroxide. 7. These data suggest that 
metabolism by catalase plays an important role in the relaxation 
induced by hydroxylamine and sodium azide in isolated rings of 
rat aorta. Relaxation appears to be due to formation of 
nitric oxide and activation of soluble guanylate cyclase. 
In contrast, metabolism by catalase does not appear to 
be involved in the relaxant actions of hydrogen peroxide 
or glyceryl trinitrate.