Pennsylvania State Heart and Vascular Institute, Department of Cellular and Molecular Physiology, General Clinical Research Center, Pennsylvania State University College of Medicine, H047, 500 Univ. Dr., Hershey, PA 17033-2390, USA.
Am J Physiol Heart Circ Physiol. 2011 Feb;300(2):H670-4. doi: 10.1152/ajpheart.00710.2010. Epub 2010 Dec 10.
Melatonin is synthesized and released into the circulation by the pineal gland in a circadian rhythm. Melatonin has been demonstrated to differentially alter blood flow to assorted vascular beds by the activation of different melatonin receptors in animal models. The purpose of the present study was to determine the effect of melatonin on blood flow to various vascular beds in humans. Renal (Doppler ultrasound), forearm (venous occlusion plethysmography), and cerebral blood flow (transcranial Doppler), arterial blood pressure, and heart rate were measured in 10 healthy subjects (29±1 yr; 5 men and 5 women) in the supine position for 3 min. The protocol began 45 min after the ingestion of either melatonin (3 mg) or placebo (sucrose). Subjects returned at least 2 days later at the same time of day to repeat the trial after ingesting the other substance. Melatonin did not alter heart rate and mean arterial pressure. Renal blood flow velocity (RBFV) and renal vascular conductance (RVC) were lower during the melatonin trial compared with placebo (RBFV, 40.5±2.9 vs. 45.4±1.5 cm/s; and RVC, 0.47±0.02 vs. 0.54±0.01 cm·s(-1)·mmHg(-1), respectively). In contrast, forearm blood flow (FBF) and forearm vascular conductance (FVC) were greater with melatonin compared with placebo (FBF, 2.4±0.2 vs. 1.9±0.1 ml·100 ml(-1)·min(-1); and FVC, 0.029±0.003 vs. 0.023±0.002 arbitrary units, respectively). Melatonin did not alter cerebral blood flow measurements compared with placebo. Additionally, phentolamine (5-mg bolus) after melatonin reversed the decrease in RVC, suggesting that melatonin increases sympathetic outflow to the kidney to mediate renal vasoconstriction. In summary, exogenous melatonin differentially alters vascular blood flow in humans. These data suggest the complex nature of melatonin on the vasculature in humans.
褪黑素由松果体按照昼夜节律合成并释放到血液中。在动物模型中，褪黑素通过激活不同的褪黑素受体，被证明可以改变不同血管床的血流。本研究旨在确定褪黑素对人体不同血管床血流的影响。10 名健康受试者（29±1 岁；5 男 5 女）仰卧位 3 分钟，测量肾脏（多普勒超声）、前臂（静脉闭塞体积描记法）和脑血流（经颅多普勒）、动脉血压和心率。在摄入褪黑素（3 毫克）或安慰剂（蔗糖）后 45 分钟开始该方案。受试者至少在 2 天后的同一时间返回，在摄入另一种物质后重复试验。褪黑素不改变心率和平均动脉压。与安慰剂相比，褪黑素试验期间肾血流速度（RBFV）和肾血管传导率（RVC）较低（RBFV，40.5±2.9 对 45.4±1.5cm/s；RVC，0.47±0.02 对 0.54±0.01cm·s(-1)·mmHg(-1)）。相比之下，与安慰剂相比，褪黑素可使前臂血流（FBF）和前臂血管传导率（FVC）增加（FBF，2.4±0.2 对 1.9±0.1ml·100ml(-1)·min(-1)；FVC，0.029±0.003 对 0.023±0.002 任意单位）。与安慰剂相比，褪黑素对脑血流测量没有影响。此外，在褪黑素后给予酚妥拉明（5mg 推注）可逆转 RVC 的降低，表明褪黑素增加了肾交感神经输出以介导肾血管收缩。总之，外源性褪黑素可使人体血管血流产生差异。这些数据表明褪黑素对人类血管的复杂作用。
