Young S N, Oravec M
Can J Biochem. 1979 Jun;57(6):517-22. doi: 10.1139/o79-065.
Growth hormone antagonizes the induction of tryptophan pyrrolase and tyrosine amino-transferase by cortisol. We have shown that contrary to previous reports, growth hormone is also capable of antagonizing the induction of these enzymes by tryptophan and alpha-methyl tryptophan. As alpha-methyl tryptophan is not metabolized appreciably in the rat, our data show that growth hormone does not act indirectly through changes in the liver tryptophan content as was suggested previously. Growth hormone decreases the rate of tryptophan catabolism in vivo after induction of tryptophan pyrrolase by tryptophan and alpha-methyl tryptophan. Because the rate of catabolism of a tryptophan is slower in animals treated with growth hormone, tissue tryptophan levels and the rate of synthesis of 5-hydroxyltryptamine in the brain are higher in these animals than in those receiving tryptophan alone. Thus, although tryptophan administration raises brain 5-hydroxytryptamine levels, induction of tryptophan pyrrolase in the liver, by the load, limits the extent and duration of the rise in brain 5-hydroxytryptamine synthesis. This has important implications for the clinical use of tryptophan in psychiatric disorders, where tryptophan is given to produce long-lasting elevations of brain 5-hydroxytryptamine.
生长激素可拮抗皮质醇对色氨酸吡咯酶和酪氨酸氨基转移酶的诱导作用。我们已表明，与先前的报道相反，生长激素也能够拮抗色氨酸和α-甲基色氨酸对这些酶的诱导作用。由于α-甲基色氨酸在大鼠体内不会被明显代谢，我们的数据表明，生长激素并非如先前所认为的那样通过改变肝脏色氨酸含量来间接发挥作用。在色氨酸和α-甲基色氨酸诱导色氨酸吡咯酶后，生长激素可降低体内色氨酸的分解代谢速率。因为在用生长激素处理的动物中色氨酸的分解代谢速率较慢，所以这些动物脑组织中的色氨酸水平以及5-羟色胺的合成速率高于仅接受色氨酸的动物。因此，尽管给予色氨酸会提高脑内5-羟色胺水平，但负荷诱导肝脏中的色氨酸吡咯酶会限制脑内5-羟色胺合成增加的程度和持续时间。这对于色氨酸在精神疾病临床应用中的意义重大，在精神疾病治疗中，给予色氨酸是为了使脑内5-羟色胺产生持久升高。
