Abstract
A histochemical method for triglyceride esters is described that depends on hydrolysis of triglycerides to fatty acids by pancreatic lipase, precipitation of the released fatty acid as calcium soap and formation of lead sulphide by the conventional Gomori technique. The specificity of the lipase for triglyceride was investigated by chromatography and activation-inhibition studies. The enzyme preparation used hydrolyzed triglycerides and waxes but did not split cholesterol esters or phosphoglycerides. Positive histochemical reactions were obtained with this pancreatic lipase method in medium sized and fine lipid droplets in frozen sections. Positive reactions were observed in rat brown fat; in various adipose tissues in man, rabbit and rat; in the spermatogonia of rat testis; in human epidermis and sebaceous glands; in solitary unidentified adrenocortical cells in man and rat; in human fatty liver and in fine droplets in senile human myocardium. A slight variable reaction was obtained in human atherosclerotic plaques. The reaction of brown fat was also investigated with the electron microscope. No triglyceride was demonstrated in unfixed tissue sectons when an active preparation of lipoprotein lipase was used in place of pancreatic lipase. This failure was probably due to diffusion of lipoprotein from unfixed sections. Lipoprotein lipase is inactive against serum lipoproteins fixed with formaldehyde or glutaraldehyde.