The impact of melatonin and its agonist on blood pressure and serum endothelin-1 in continuous light and pinealectomized rats.

The present study investigates the roles of melatonin (MEL) and its agonist ramelteon (RAM) on blood pressure regulation, nitric oxide (NO), and oxidative stress and plasma endothelin-1(ET-1) levels in continuous light exposure and pinealectomized conditions. This study includes two experiments. The first experiment involved control, continuous light emitting diode (LED) exposure, continuous LED + MEL administration, and continuous LED + RAM. The second experiment included control, pinealectomy, pinealectomy + MEL administration, pinealectomy + RAM administration, and pinealectomy + continuous LED exposure. The present results showed significant increase of systolic blood pressure (SBP) of continuous LED exposure group, pinealectomy, and pinealectomy with continuous LED exposure. On the contrary, MEL and RAM both decreased SBP. Additionally, the continuous LED exposure considerably increased malondialdehyde (MDA). However, MEL increased both plasma ET-1 slightly and ET-1 significantly but RAM dramatically increased ET-1. While, both of MEL and RAM decreased MDA. In the second experiment, while MDA dramatically increased after pinealectomy and pinealectomy with LED illumination, ET-1 and NO were only a little reduced. Melatonin elevated plasma ET-1 and NO significantly. While, MDA was greatly reduced by MEL but not by RAM. The results suggested that MEL and RAM could attenuate SBP mostly via increasing NO generation and oxidative stress reduction.