THYMUS INFLUENCES LIVER FUNCTIONS THROUGH HYPOTHALAMUS-PITUITARY-GONAD AXIS IN RATS

The aim of the review is to summarize our recent studies on the influe nce of the thymus on liver functions and its intermediary pathway in r ats. Young adult thymectomized rats were used as a model in the experi ments, and either thymic peptides or sex hormones were supplemented to these animals. Liver microsomal cytochrome P-450 and aminopyrine-N-de methylase (ADM) activities were decreased in thymectomized rats, and t he change in the male was more significant than that in female rats. A n increase of liver malondialdehyde (MDA) and a decrease of liver glut athione (GSH) and superoxide dismutase activity were observed in the f emale thymectomized rats, but not in the males. Accompanied by the inc rease of MDA, a decline of membrane fluidity of liver microsomes and m itochondria and a decrease of Ca2+ uptake by liver microsomes were exh ibited in the female thymectomized rats. Subcutaneous injection of thy mic peptides decreased MDA level, and increased GSH content, membrane fluidity and Ca2+ uptake by microsomes in the liver of thymectomized r ats. On the other hand, male thymectomized rats showed a decrease of h ypothalamic luteinizing hormone-releasing hormone (LHRH), plasma lutei nizing hormone (LH) and testosterone levels, Subcutaneous injection of testosterone propionate to these animals restored their liver P-450 a nd ADM activities to normal levels. Female thymectomized rats exhibite d a decline of hypothalamic LHRH and plasma estradiol levels. Suppleme ntation of estradiol benzoate reversed the increase of liver MDA in th ese animals. The data suggest that the thymus may influence liver func tions through the hypothalamus-pituitary-gonad axis. Thus, a new 'thym us-neuroendocrine-liver pathway' is proposed, which may account for th e significance of the thymus in maintaining homeostasis and integrativ e functions in the body. Copyright (C) 1996 Elsevier Science Ltd.