Melatonin is released by the pineal gland and can modulate cardiovascular system function via the G protein-coupled melatonin receptors MT₁ and MT₂. Most vessels are surrounded by perivascular adipose tissue (PVAT), which affects their contractility. The aim of our study was to evaluate mRNA and protein expression of MT₁ and MT₂ in the mesenteric artery (MA) and associated PVAT of male rats by RT-PCR and Western blot. Receptor localization was further studied by immunofluorescence microscopy. Effects of melatonin on neurogenic contractions were explored in isolated superior MA ex vivo by measurement of isometric contractile tension. MT₁, but not MT₂, was present in MA, and MT₁ was localized mainly in vascular smooth muscle. Moreover, we proved the presence of MT₁, but not MT₂ receptors, in MA-associated PVAT. In isolated superior MA with intact PVAT, neuro-adrenergic contractile responses were significantly smaller when compared to arteries with removed PVAT. Pre-treatment with melatonin of PVAT-stripped arterial rings enhanced neurogenic contractions, while the potentiating effect of melatonin was not detected in preparations with preserved PVAT. We hypothesize that melatonin can stimulate the release of PVAT-derived relaxing factor(s) via MT₁, which can override the direct pro-contractile effect of melatonin on vascular smooth muscle. Our results suggest that melatonin is involved in the control of vascular tone in a complex way, which is vessel specific and can reflect a sum of action on different layers of the vessel wall and surrounding PVAT.

褪黑激素由松果体释放，可通过 G 蛋白偶联褪黑激素受体 MT ₁和 MT ₂调节心血管系统功能。大多数血管被血管周围脂肪组织（PVAT）包围，这会影响它们的收缩性。我们研究的目的是通过 RT-PCR 和 Western blot 评估雄性大鼠肠系膜动脉 (MA) 中 MT ₁和 MT ₂的 mRNA 和蛋白表达以及相关的 PVAT。通过免疫荧光显微镜进一步研究受体定位。通过测量等长收缩张力，在离体分离的上 MA 中探讨了褪黑激素对神经源性收缩的影响。 MA中存在MT ₁ ，但不存在MT ₂ ，并且MT ₁主要位于血管平滑肌中。此外，我们证明在MA相关的PVAT中存在MT ₁受体，但不存在MT ₂受体。在具有完整 PVAT 的孤立上 MA 中，与去除 PVAT 的动脉相比，神经肾上腺素能收缩反应明显较小。用褪黑激素预处理PVAT剥离的动脉环可增强神经源性收缩，而在保留PVAT的制剂中未检测到褪黑激素的增强作用。我们假设褪黑激素可以通过 MT ₁刺激 PVAT 衍生的松弛因子的释放，这可以克服褪黑激素对血管平滑肌的直接促收缩作用。我们的结果表明，褪黑激素以复杂的方式参与血管张力的控制，这是血管特异性的，可以反映对血管壁不同层和周围PVAT的作用总和。