Melatonin inhibits endothelial nitric oxide production in vitro
Version of Record online: 1 AUG 2006
Journal of Pineal Research
Volume 41, Issue 3, pages 267–274, October 2006
How to Cite
Tamura, E. K., Silva, C. L. M. and Markus, R. P. (2006), Melatonin inhibits endothelial nitric oxide production in vitro. Journal of Pineal Research, 41: 267–274. doi: 10.1111/j.1600-079X.2006.00366.x
- Issue online: 1 AUG 2006
- Version of Record online: 1 AUG 2006
- Received March 23, 2006; accepted June 14, 2006.
- confocal microscopy;
- nitric oxide
Abstract: Endothelial cell function is a major player on the regulation of both vascular tonus and permeability. Activation of nitric oxide synthase (NOS) by bradykinin is one physiological pathway for the well-known vascular relaxation mediated by endothelial-derived nitric oxide (NO). In this study we investigated if melatonin, which is known to modulate endothelial cell function and NO production in other tissues, is able to impair bradykinin-induced NO production in vitro. Rat microvascular endothelial cells were incubated with fluorescent dyes to detect either NO or Ca2+. In addition, cGMP levels were measured by enzyme immunoassay. We found that while bradykinin (1–100 nm) increased both cytosolic Ca2+ and NO production, melatonin (1 nm) abolished this NO production but not cytosolic Ca2+ elevation. N-acetylserotonin (0.1 and 1 nm) had the same effect, while the selective agonist for MT3 receptors (5-MCA-NAT, 1 nm) had no effect. Moreover, nonselective and MT2-selective antagonists did not alter the effect of melatonin, suggesting that it is not mediated by MT melatonin receptors. A possible direct inhibition of calmodulin was also discarded as melatonin did not mimic the effect of calmidazolium on cytosolic Ca2+. Melatonin also abolished cGMP production induced by 1 μm bradykinin, indicating that the NO downstream effect is impaired. Thus, here we show that melatonin reduces NO production induced by bradykinin by a mechanism upstream to the interaction of Ca2+–calmodulin with NOS. Moreover, this effect might be the basis of the diurnal variation in endothelial cell function.