Therapeutic concentrations of raloxifene augment nitric oxide-dependent coronary artery dilatation in vitro.
OBJECTIVE
Raloxifene improves cardiovascular function. This study examines the hypothesis that therapeutic concentrations of raloxifene augment endothelium-dependent relaxation via up-regulation of eNOS expression and activity in porcine coronary arteries.


METHODS
Isometric tension was measured in rings from isolated arteries. Intracellular Ca(2+) concentrations ([Ca(2+)](i)) in arterial endothelial cells were detected by Ca(2+) fluorescence imaging. Phosphorylation of eNOS at Ser-1177 was assayed by Western blot analysis.


RESULTS
In arterial rings pre-contracted with 9,11-dideoxy-11alpha,9alpha-epoxy-methano-prostaglandin F(2alpha) (U46619), treatment with raloxifene (1-3 nM) augmented bradykinin- or substance P-induced relaxation and this effect was antagonized by ICI 182,780, an estrogen receptor antagonist. The enhanced relaxation was abolished in rings treated with inhibitors of nitric oxide/cyclic GMP-dependent dilation, N(G)-nitro-L-arginine methyl ester (L-NAME) plus 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). In contrast, effects of raloxifene were unaffected after inhibition of endothelium-derived hyperpolarizing factors by charybdotoxin plus apamin. Raloxifene (3 nM) did not influence endothelium-independent relaxation to sodium nitroprusside. 17beta-Estradiol (3-10 nM) also enhanced bradykinin-induced relaxation, which was inhibited by ICI 182,780. Treatment with raloxifene (3 nM) did not affect bradykinin-stimulated rise in endothelial cell [Ca(2+)](i). Raloxifene, 17beta-estradiol, and bradykinin increased eNOS phosphorylation at Ser-1177 and ICI 182,780 prevented effects of raloxifene or 17beta-estradiol but not that of bradykinin. Raloxifene had neither additive nor antagonistic effects on 17beta-estradiol-induced eNOS phosphorylation.


CONCLUSIONS
Raloxifene in therapeutically relevant concentrations augmented endothelial function in porcine coronary arteries in vitro through ICI 182,780-sensitive mechanisms that were associated with increased phosphorylation of eNOS but independent of changes in endothelial cell [Ca(2+)](i).
Leung
F P
FP
Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong SAR, China.
Yung
L M
LM
Leung
H S
HS
Au
C L
CL
Yao
X
X
Vanhoutte
P M
PM
Laher
I
I
Huang
Y
Y
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D000077267:Fulvestrant; D066298:In Vitro Techniques; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D020849:Raloxifene Hydrochloride / Q000494:pharmacology*; D013552:Swine; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
D004965:Estrogen Antagonists; D014665:Vasodilator Agents; D000077267:Fulvestrant; D009569:Nitric Oxide; D020849:Raloxifene Hydrochloride; D004958:Estradiol; D052250:Nitric Oxide Synthase Type III; D001920:Bradykinin