The effect of ageing on the metabolism of the infective larvae ofStrongyloides rattiSandground, 1925

Abstract

The infective larvae ofS. rattihad a high Q_{o2(9·8 μl/mg dry weight/h at 20 °C). Their R.Q. was 0·74 indicating that lipid was the main metabolite.As the infective larvae aged there was an exponential decrease in their infectivity and a corresponding decrease with age in the Qo2rate of activity and rate of substrate utilization. The R.Q. of fresh and aged larvae was the same showing that there was no change in the substrate being utilized.The infective larvae ofS. ratticontained 25% lipid 3% glycogen and 0·25% free sugars (dry weight). The free sugars consisted of glucose and trehalose in approximately equal amounts. Both lipid and glycogen decreased as the larvae aged.Analyses showed all the normal lipid components to be present, the major lipid fraction detected was free fatty acid. As the larvae aged there was a big decrease in the amounts of triglyceride and free fatty acid. There was, however, no difference in the amounts of cholesterol or in the phospholipid composition of fresh and aged larvae.The fatty-acid composition of the larvae was analysed; 68% of the total fatty acids were unsaturated and the major fatty acid was C18:1. As the larvae aged, the fatty acids were not all catabolized at the same rate; the acid C18:1was the most heavily catabolized decreasing by 75% in 8 days, whilst C20:1decreased by only half this amount in the same time.The distribution of lipid and glycogen was investigated histochemically. Lipid droplets were confined to the posterior two-thirds of the infective larvae and occurred in the lateral lines, non-contractile parts of the muscles and in the cells of the intestine. As the larvae aged the lipid in the body wall and lateral lines disappeared first. Dark granules, possibly excretory products, accumulated in old larvae. Glycogen was found in the lateral lines throughout the length of the larva.I should like to thank Dr P. Tate for his constant advice and encouragement. This work was carried out during the tenure of a Medical Research Council scholarship.}