Y. Okatani et al., Melatonin inhibits vasospastic action of oxidized low-density lipoprotein in human umbilical arteries, J PINEAL R, 29(2), 2000, pp. 74-80
We evaluated the antioxidant property of melatonin in countering the vasosp
astic effect of oxidized low-density lipoprotein (ox-LDL), which has been r
eported to be the most important risk factor for atherosclerosis and also m
ay be linked to preeclampsia. Helical sections of umbilical arteries were o
btained from human placentas at elective cesarean deliveries between 37 and
39 weeks of gestation. Changes in maximal tension induced by potassium chl
oride were measured in arterial sections with intact endothelium. ox-LDL (2
00 or 300 mu g protein/mL) increased vascular tension by 15.6 +/- 2.3 or 31
.9 +/- 4.0%, respectively. In contrast, native LDL only slightly increased
vascular tension (2.7 +/- 1.0% for 200 mu g protein/mL and 6.0 +/- 1.7% for
300 mu g protein/mL). Pretreatment with L-N-G-monomethyl-arginine (2 x 10(
-4) M) significantly reduced the vasospastic effect of ox-LDL, as did pretr
eatment with mannitol (30 mM). Melatonin (10 mu M) significantly reduced th
e vasospastic effect of ox-LDL. These findings suggest that ox-LDL potentia
tes vascular tension in the human umbilical artery, possibly by suppressing
endothelial synthesis of nitric oxide. Melatonin significantly suppressed
the vasospastic effect of ox-LDL, probably because it scavenges hydroxyl ra
dical arising from ox-LDL.