Original articleExogenous melatonin reduced blood pressure in late-term ovine fetus via MT1/MT2 receptor pathways

Melatonin is involved in the regulation of blood pressure through the receptor dependent or independent route. However, the effect of melatonin on fetal blood pressure is unknown. This study investigated the effect of melatonin on blood pressure of the late-term ovine fetus in utero. Melatonin and/or antagonists were intravenously administered into the fetuses. Mean arterial pressure and heart rate were recorded. Fetal blood samples were analyzed for biochemical parameters and hormones, including cortisol, angiotensin I, angiotensin II, aldosterone, atrial natriuretic peptide, corticotrophin-releasing hormone, adrenocorticotropic hormone, and endothelin. Fetal blood pressure was decreased following administration of melatonin, whereas it was increased following administration of luzindole, but not prazosin. Plasma level of endothelin was decreased by melatonin, which was blocked by luzindole. Our study suggested that melatonin reduced fetal blood pressure via MT1/MT2 receptors and possibly involving release of endothelin.