English J, Bojkowski C J, Poulton A L, Symons A M, Arendt J
Department of Biochemistry, University of Surrey, Guildford, Surrey, England.
J Pineal Res. 1987;4(4):351-8. doi: 10.1111/j.1600-079x.1987.tb00874.x.
The pineal hormone melatonin has been used to advance the onset of the breeding season in sheep and thus produce lambs earlier in the year. If this reproductive manipulation is to be used commercially, some knowledge of the route of metabolism and identity of possible metabolites is necessary. A major metabolite of melatonin in rodents and man is 6-hydroxymelatonin sulphate (acetyl-methoxytryptamine-6-sulphate [aMT6S]). No significant amounts of this metabolite could be found in the plasma of untreated ewes. After subcutaneous implantation of melatonin for 5 months, plasma levels of aMT6S were also insignificant. On the other hand, both a single oral dose of melatonin (3 mg) and daily oral dosing gave rise to circulating levels of aMT6S in the range of 150 to 1,500 pg/ml for at least 18 h. The profiles seen after 180 days treatment were similar to those seen after a single dose, indicating that this route of melatonin metabolism is not induced by chronic administration. Intravenous injection of melatonin (200 or 20 micrograms) gave rise to detectable levels of aMT6S in the plasma. These results indicate that the quantitative aspects of melatonin metabolism differ according to the route of administration.
松果体激素褪黑素已被用于提前绵羊繁殖季节的开始时间，从而在一年中更早地产下羊羔。如果这种生殖调控要用于商业用途，就需要了解其代谢途径以及可能的代谢产物的特性。在啮齿动物和人类中，褪黑素的一种主要代谢产物是6-羟基褪黑素硫酸盐（乙酰 - 甲氧基色胺 - 6 - 硫酸盐 [aMT6S]）。在未经处理的母羊血浆中未发现大量这种代谢产物。在皮下植入褪黑素5个月后，血浆中aMT6S的水平也很低。另一方面，单次口服褪黑素（3毫克）和每日口服给药都会使血浆中aMT6S的循环水平在150至1500皮克/毫升范围内至少持续18小时。180天治疗后的情况与单次给药后的相似，这表明这种褪黑素代谢途径不会因长期给药而被诱导。静脉注射褪黑素（200或20微克）会使血浆中出现可检测到的aMT6S水平。这些结果表明，褪黑素代谢的定量方面因给药途径而异。
