Regulation of Expression of Liver Alcohol Dehydrogenase

Crabb, David

Abstract

The major determinants of the pharmacological, addictive, and pathological effects of alcohol consumption are the tissue concentrations of ethanol and its metabolic products, and the duration of exposure to these compounds. There are significant variations in individual alcohol elimination rates among human subjects. The activity of liver alcohol dehydrogenase (ADH) is an important determinant of alcohol elimination rate and may be controlled by the kinetic properties of ADH isoenzymes and by the total liver content of ADH. The rat is a useful animal model for studies on the regulation of liver ADH content because it exhibits only two major molecular forms of ADH and the total enzyme activity is under genetic, developmental and endocrine control. In order to understand the mechanisms of regulation of liver ADH activity in rats, the following studies will be performed: 1) The two purified molecular forms of liver ADH will be characterized by peptide mapping and kinetic analysis. These studies are necessary to interpret later experiments involving measurement of levels ADH mRNA. 2) The differences in liver ADH activity between Sprague-Dawley and ACI/N rates will be examined by a) determining the molecular properties and peptide maps of purified enzyme from each strain, b) evaluating the mode of inheritance of this trait by classical genetic crosses of F1 offspring and parental strains and c) measuring the turnover of ADH and levels of ADH mRNA in the two strains to determine whether the difference in activity is due to differences in rates of synthesis or degradation. 3) The role of thyroid hormone in the developmental control of ADH activity will be assessed by evaluating the effect of propylthiouracil-induced hypothyroidism in neonatal rats and by measuring ADH turnover and mRNA levels in thyroidectomized animals. 4) The newly discovered role of the pituitary in the sexually differentiated expression of ADH will be examined by a) chronically infusing growth hormone into male and female rats, b) determining the effect on ADH activity of electrolytic lesions of the hypothalamus which are known to increase growth hormone secretion and c) evaluating the effect of neonatal androgen exposure which is known to influence subsequent patterns of pituitary hormone secretion in adult animals. 5) To establish a simpler system for the study of hormonal control of liver ADH activity, primary hepatocyte cultures will be used to determine the medium, serum, and hormone requirements for normal rates of ADH synthesis.