Cupo M A, Donaldson W E
Department of Poultry Science, North Carolina State University, Raleigh 27695-7608.
Drug Nutr Interact. 1988;5(4):297-308.
Studies were conducted to investigate the effects of lead and niacin on tryptophan and serotonin metabolism in growing broiler chicks. A low-niacin basal diet based on soybean meal and glucose was supplemented with either 40 ppm niacin/kg feed or 2,000 ppm lead, as lead acetate trihydrate, or a combination of the two in a 2 x 2 factorial arrangement. The experimental diets were fed from 1 day to 3 weeks of age. The activities of several enzymes involved in tryptophan and serotonin metabolism were assayed in chicks fed each of the experimental diets. Lead reduced the activity of liver tryptophan pyrrolase but had no effect on the activity of hepatic picolinic carboxylase. Low dietary niacin had no effect on the activity of either of these enzymes. Brainstem tryptophan 5-hydroxylase activity was unaltered by either lead or niacin. Brain and liver monoamine oxidase activity was reduced by lead but was not affected by niacin. No interactions of lead and niacin were observed with any of the enzymes examined. Lead had no consistent effect on brain serotonin (5-HT) steady-state level, but it increased the level of the major metabolite of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA). Monoamine oxidase blockade failed to reduce the elevated 5-HIAA level in lead-treated chicks. The drug probenecid produced an increase in 5-HIAA that was comparable to the increase caused by lead. The effects of probenecid and lead were additive. It is concluded that lead significantly altered the activity of several enzymes involved with tryptophan metabolism, whereas the dietary niacin levels employed were without effect. Additionally, lead caused the accumulation of 5-HIAA in the brain, which appeared to result from inhibition of the probenecid-sensitive acid transport system.
开展了多项研究，以调查铅和烟酸对生长中的肉鸡雏鸡色氨酸和血清素代谢的影响。以豆粕和葡萄糖为基础的低烟酸基础日粮，分别添加40 ppm烟酸/千克饲料或2000 ppm铅（以三水合醋酸铅形式），或二者按2×2析因设计组合添加。从1日龄至3周龄饲喂实验日粮。对采食每种实验日粮的雏鸡体内参与色氨酸和血清素代谢的几种酶的活性进行了测定。铅降低了肝脏色氨酸吡咯酶的活性，但对肝脏吡啶羧酸羧化酶的活性没有影响。低日粮烟酸水平对这两种酶的活性均无影响。脑干色氨酸5-羟化酶的活性不受铅或烟酸的影响。铅降低了脑和肝脏单胺氧化酶的活性，但不受烟酸的影响。未观察到铅和烟酸与所检测的任何一种酶之间存在相互作用。铅对脑血清素（5-羟色胺，5-HT）稳态水平没有一致的影响，但增加了5-HT的主要代谢产物5-羟吲哚乙酸（5-HIAA）的水平。单胺氧化酶阻断未能降低铅处理雏鸡中升高的5-HIAA水平。药物丙磺舒使5-HIAA增加，其增加程度与铅引起的增加程度相当。丙磺舒和铅的作用是相加的。得出的结论是，铅显著改变了几种参与色氨酸代谢的酶的活性，而所用的日粮烟酸水平没有影响。此外，铅导致脑中5-HIAA积累，这似乎是由于对丙磺舒敏感的酸转运系统受到抑制所致。
