Martín F J, Atienza G, Aldegunde M, Míguez J M
Departamento de Fisioloxía, Facultade de Bioloxía, Universidade de Santiago de Compostela, Spain.
Life Sci. 1993;53(13):1079-87. doi: 10.1016/0024-3205(93)90261-z.
The present study was conducted to examine whether melatonin impairs serotonin (5HT) release and uptake in rat platelets. Exposure of platelet-rich plasma samples (PRP) to melatonin induced a concentration-dependent inhibition of 5HT uptake and the value of IC50 was 1.3 x 10(-3) M. We have also investigated the melatonin effect on the kinetic parameters of platelet 5HT uptake. Transport capacity was inhibited (Vmax;
2.28 +/- 0.52, Melatonin: 0.74 +/- 0.13 pmol/10(7) platelet.min; p < 0.05) while the affinity of 5HT for its uptake carriers remained unaltered, thus indicating a non-competitive effect. Studies carried out to determine the existence of a differential morning (8:00h)-evening (21:00h) melatonin effect showed a higher platelet uptake sensitivity at 8:00h (two-way ANOVA, p < 0.001). Spontaneous 5HT release was not impared by the hormone and no daily variation in sensitivity was detected. The possible mechanism of action of melatonin on platelet transport is discussed, and the results support the suitability of the platelet model for studying sensitivity changes in target cells to the hormone.
本研究旨在检测褪黑素是否会损害大鼠血小板中血清素（5-羟色胺，5HT）的释放和摄取。富含血小板的血浆样本（PRP）暴露于褪黑素后，会引起5HT摄取的浓度依赖性抑制，半数抑制浓度（IC50）值为1.3×10⁻³M。我们还研究了褪黑素对血小板5HT摄取动力学参数的影响。转运能力受到抑制（最大反应速度Vmax；对照组：2.28±0.52，褪黑素组：0.74±0.13 pmol/10⁷个血小板·分钟；p<0.05），而5HT对其摄取载体的亲和力保持不变，因此表明这是一种非竞争性效应。为确定早晨（8:00）-晚上（21:00）褪黑素效应差异的存在而进行的研究表明，8:00时血小板摄取敏感性更高（双向方差分析，p<0.001）。激素并未损害5HT的自发释放，且未检测到敏感性的每日变化。讨论了褪黑素对血小板转运的可能作用机制，结果支持血小板模型适用于研究靶细胞对该激素的敏感性变化。
