Thyroid Hormone Modulates the Expression of Rat Liver Gammaglutamyl transpeptidase Activity

Summary

Gammaglutamyltranspeptidase (GGT) activity is considered as a marker of liver phenotype, being maximally expressed in fetal liver and virtually absent in adult mature tissue. Since thyroid hormone has been identified to influence growth and development of almost all tissues, we have investigated the possible involvement of such factors in regulating rat hepatic GGT. Our results indicate that the activity of GGT in liver of perinatal hypothyroid rats is low as well as in control animals; instead, it is greatly increased in adult hypothyroid rats compared to controls of the same age (+260% in 2-month-old hypothyroid rats). Replacement therapy with T₃ to hypothyroid rats normalizes the enzyme activity to the levels of control animals. Thyroid hormone appears to modulate the gene expression of the enzyme, since in the different thyroid status GGT mRNA level closely parallels the variations of the enzyme activity. These results further suggest that thyroid hormone plays a crucial role in maintaining the phenotype of adult liver tissue.

Key words

Thyroid Hormone - GGT Expression - Rat Liver