Ramelteon (TAK-375) is a Melatonin Receptor Agonist. The mechanism of action of ramelteon is as a Melatonin Receptor Agonist.

MT2 receptor:112 pM(Ki), MT receptor (chicken):23.1 pM(Ki), MT1 receptor:14 pM(Ki)

Ramelteon（0.03 mg/kg和0.3 mg/kg,p.o.）显著缩短了入睡潜伏期,并显著增加了自由活动猴子的总睡眠时间,且不影响猴子的日常行为.腹腔注射给药大鼠10 mg/kg Ramelteon,显著降低降低大鼠的NREM睡眠潜伏期,并且还产生非快速眼动（NREM）睡眠持续时间的短暂增加,但是NREM功率谱未变.

Ramelteon抑制非洲爪蟾的黑色素细胞色素颗粒聚集,pEC50为11.48。1 nM Ramelteon不仅增加MT1/MT2小脑颗粒细胞的ERK1/2磷酸磷酸化,也增加只含一个褪黑激素受体的小脑颗粒细胞的ERK1/2磷酸磷酸化。Ramelteon抑制forskolin刺激的cAMP产生,在CHO细胞中IC50为21.2 pM。 4P-PDOT阻断Ramelteon（1 nM）对MT1 KO小脑颗粒细胞的刺激作用,而luzindole则减弱Ramelteon（1 nM）在MT2 KO小脑颗粒细胞中的作用。Ramelteon与重组人MT1和MT2受体具有高亲和力,pKi分别为10.05和9.70。

cDNA encoding the human MT1 gene is introduced into CHO cells. Cells are harvested at confluence in Ca2+ and Mg2+ free Hanks' balanced salt solution containing 5 mM EDTA and collected by centrifugation. Cells are homogenized in ice-cold 50 mM Tris–HCl buffer, washed twice, pelleted, and stored at -30°C until the binding assays are conducted. Test compound and 40 pM 2-[ 125I]melatonin are mixed with the thawed homogenate in a total volume of 1 mL and incubated at 25°C for 150 min. The reaction is terminated by addition of 3 mL of icecold buffer followed by vacuum filtration on a Whatman GF/B. The filter is washed twice and radioactivity is counted by a g-counter[1].