Kpj. Okane et al., LOCAL L-N-G-MONOMETHYL-ARGININE ATTENUATES THE VASODILATOR ACTION OF BRADYKININ IN THE HUMAN FOREARM, British journal of clinical pharmacology, 38(4), 1994, pp. 311-315
1 Studies in animals indicate that bradykinin relaxes blood vessels di
rectly through an action on smooth muscle and indirectly through the r
elease of endothelium-derived mediators. Its precise mechanism of acti
on in the human arterial circulation is not yet known. 2 In this study
the effects of a specific inhibitor of nitric oxide synthase, L-N-G-m
onomethyl-arginine (L-NMMA) and noradrenaline on the vasodilator respo
nses to bradykinin were examined in the forearm arterial bed of health
y volunteers. Noradrenaline was used as a control for vasoconstriction
by L-NMMA; glyceryl trinitrate (GTN) as a control vasodilator acting
independently of the NO synthase enzyme. 3 L-NMMA (4 mu mol min(-1); 5
min) alone reduced resting forearm blood flow by 44% (P < 0.01; n = 6
) confirming that nitric oxide plays an important role in regulating v
ascular tone. 4 Bradykinin (10 and 100 pmol min(-1); 3 min each dose)
and GTN (2 and 5 nmol min(-1); 3 min each dose) increased forearm bloo
d flow in a dose-dependent manner (percentage changes 171 +/- 17% and
398 +/- 35%, and 176 +/- 21% and 268 +/- 42%, respectively; n = 6). 5
The response to bradykinin, but not that to GTN, was attenuated by L-N
MMA compared with noradrenaline (P < 0.05; n = 6), suggesting that bra
dykinin-induced vasodilatation in the forearm is mediated, at least in
part, by stimulating release of nitric oxide.