A. Pistelli et al., NITROBLUE TETRAZOLIUM INHIBITS OXIDATION OF GLYCERYL TRINITRATE TO NITRIC-OXIDE IN BOVINE AORTIC SMOOTH-MUSCLE CELLS, Biochemical pharmacology, 47(10), 1994, pp. 1737-1742
The effects of nitroblue tetrazolium (NBT), a well-known scavenger of
superoxide anions and an inhibitor of nicotinamide adenine dinucleotid
e (NADPH)-dependent oxidations, were assessed on the metabolism of gly
ceryl trinitrate (GTN) to nitric oxide (NO) by bovine aortic smooth mu
scle cells (SMC). The extent of this metabolism was determined by meas
uring NO formed, using the inhibition of thrombin-induced platelet agg
regation and relaxation of rabbit aortic strips as bioassay systems. I
n addition, NO produced from GTN by SMC was measured as nitrite (NO2-)
, one of its breakdown products. The antiplatelet effect of GTN (44 mu
M) was potentiated by SMC (0.12-0.46 x 10(5) cells) treated with indo
methacin (10 mu M) and this was inhibited in a concentration-dependent
manner when the cells were pretreated with NBT (100 mu M). NBT (3-100
mu M) also reduced the formation of NO2- from GTN (600 mu M) by SMC (
3 x 10(5) cells). Furthermore, relaxations of endothelium-denuded stri
ps of the rabbit aorta by GTN (10(-9)-10(-6) M) were attenuated when t
he strips were pretreated with NBT (100 or 500 mu M). The formation of
NO from L-arginine (L-Arg) by SMC was not affected by NBT. The hypote
nsive responses to GTN (0.25-1 mg/kg, i.v.) in anaesthetized rats were
inhibited by pretreatment with NBT (1.25 mg/kg, i.v.) but NBT did not
alter the hypotensive responses induced by SIN-1. Thus, NBT inhibited
the bioconversion of GTN to NO both in vitro and in vivo. NBT may be
a useful pharmacological tool to investigate the enzymic pathway(s) in
volved in the conversion of GTN to NO by smooth muscle cells or other
cells.