昆虫神经毒素的研究:酪胺为DDT麻痹的(虫非)蠊血淋巴毒素

1952年Sternburg及Kearns报道在DDT中毒麻痹的美洲(虫非)蠊血淋巴中存在着一种毒素,初步鉴定为芳香胺。1972年Tashiro等鉴定它为L-亮氨酸,它可脱羧成为异戊胺,具有更强的神经活性。 本工作使用了Sternburg及Tashiro所用的三套层析系统,用亮氨酸、异戊胺、酪氨酸、酪胺、苯乙胺作为标准样品来比较,发现这一毒素可能是酪胺。酪氨酸及亮氨酸均为正常成分,在对照组及处理组的三个系统中均存在。异戊胺在处理组的第一及第二系统中不存在,说明其不是毒素。只有酪氨及苯乙胺在对照组的第一、第二系统中存在,在第三系统中不存在。但在处理组中三套系统中均存在,说明它们乃是处理所产生的物质。高压液相色谱的检测证明了酪氨本身在正常昆虫中也以微量存在,但在DDT处理后,量有极大的增加。讨论了①毒素是酪胺的可能性,②毒素可能不是单一成分,③酪胺的作用机制,及④酪胺的生成与代谢。

STUDIES ON INSECT NEUROTOXIN: TYRAMINE AS THE NEUROTOXIN RELEASED IN THE HAEMOLYMPH OF DDT PROSTRATE COCKROACHES.

Sternburg and Kearns (1952) reported the presence of a neurotoxin in the haemolymph of DDT prostrate cockroaches, which is not DDT nor its metabolites. It stimulates the nerve to produce repetitive discharges and eventually blocks nerve conduction at high concentration. The neurotoxin was preliminarily identified to bean aromatic amine (Sternburg, 1960; Hawkins and Sternburg, 1964). In 1972, Tashiro et al reidentified the neurotoxin as L-le-ucine, and in a later paper (Tashiro et al 1975) they reported that L-leucine is decarboxyla-ted into isoamylamine which is more potent than L-leucine. They beleived that while the neurotoxin is L-leucine, the active agent which actually acts on the nerve is isoamylamine.We used the same three chromatographic systems of Sternburg and Tashiro, with standard samples of L-leucine, isoamylamine, tyrosine, tyramine and phenyl ethylamine and identified the neurotoxin as tyramine. Tyrosine and leucine are both normal constituents, they are found in both the control and the DDT treated groups in all the three systems. Isoamylamine is not found in the treated group in system I and II, suggesting that it is not the neurotoxin since it is absent in the haemolymph of the treated insects. Only tyramine and phenyl ethylamine are present in systems I and II in both the control and treated groups, but in system III, they are only found in the treated group. So they are newly produced by the treat ment, and seem to be the neurotoxin While both of them exhibit distinct electrophy-siological action on insect nerve, phenyl ethylamine is unique in producing almost immediate block of nerve conduction without excitation. So tyramine seems to be the only candidate for the neurotoxin.High performance liquid chromatography revealed that tyramine is also normally present but in trace amounts, and increases greatly after DDT treatment.Teh following aspects have been discussed: 1. the identity of the neurotoxin, and the cause for the difference of our present investigation with previous work, 2. the possibility of the neurotoxin being a composite, consisting of many amines, such as phenyl ethylamine, and amino acids; 3. the mode of action of tyramine; and 4, the origin and metabolism of tyramine.