Histological and histochemical studies on the effect of experimentally induced hyperthyroidism by l-thyroxine on the liver of the female albino rat

ABSTRACT

Eighteen female albino rats of an average weight 200 gm were used to study the histological and histochemical changes in the liver produced by experimentally induced hyperthyroidism. 12 animals were given a daily oral dose of 100 mu g L-thyroxine for 3 and 4 months. Whereas, 6 age-matched animals served as controls. Experimentally induced hyperthyroidism elicited marked histological changes in the liver that were more pronounced in animals with induced hyperthyroidism for 4 months. The Glisson's capsule was thickened. The central veins were congested and occasionally surrounded by mononuclear cellular infiltration. They were surrounded by increased collagenus fibers that extended around some adjacent hepatocytes. The blood sinusoids of the liver, especially those located in the subcapsular region, presented a very marked dilatation and congestion. Whereas, the hepatocytes, especially those located underneath the Glisson's capsule, were apparently markedly enlarged. This was confirmed by the morphometric study. Moreover, the number of binucleated hepatocytes were increased and occasional mitotic figures were observed. The enlarged hepatocytes presented an intense P.A.S. positive material in their cytoplasm, indicating probably an increase in their glycogen content. The hepatocytes in the peripheral parts of a few hepatic lobules showed vacuolation of their cytoplasm that appeared in both hematoxylin and eosin and P.A.S. stained sections, suggesting a fatty change. Whereas, the portal tracts were markedly enlarged and even extended between the hepatic lobules. They presented an intense mononuclear infiltration, many sections of bile ducts and widely dilated and congested blood vessels. Increased collagenous fibers were detected in the portal tracts that were surrounded by prominent and thick periportal collagenous fibers which extended to surround some adjacent hepatocytes. As regards to the histochemical study, the succinic dehydrogenase enzyme activity, compared to that of the control animals, showed an increased activity which was more marked in animals with induced hyperthyroidism for 4 months