Search

Rat liver microsomes, NADPH-regenerating system, and 1beta, 2beta-3H-testosterone have been incubated in vitro. The loss of tritium from the steroid, associated with aromatization of testosterone, was linear with time for 20 min and required NADPH. Pre-treatment of the rats with thioacetamide raised the liberation of tritium from 1beta, 2beta-3H-testosterone. The results suggest that liver damage by thioacetamide in rats may give rise to increased aromatization of testosterone.

The intestinal absorption and biotransformation of ethinylestradiol and of ethinylestradiol glucuronide in rats were studied using a jejunal loop preparation in situ. Radioactivity associated with ethinylestradiol almost completely appeared in the venous outflow within 80 min. Forty two percent was present as unchanged compound, 56% in the glucuronide fraction and 2% as sulfate ester. Absorption of ethinylestradiol glucuronide was about 20 times slower than absorption of the nonconjugated molecule. The data indicate, that intestinal absorption of ethinylestradiol involves several superimposed kinetics and that glucuronidation in the gut may result in a decreased bioavailability of the compound.

Isolated intestinal mucosa cells of the guinea pig were employed to study intestinal transport of bile acids. Chenodeoxycholate and lithocholate were rapidly taken up into jejunal and ileal cells by diffusion. Taurocholate and cholate however showed only a minor diffusion rate and were preferentially taken up by the ileal bile acid carrier. This uptake was saturable with an apparent Km of 231 microM and V of 7 nmol/mg protein per min for taurocholate; this bile acid was accumulated 90-fold. Its uptake was strongly inhibited by antimycin A, FCCP, ouabain or Na+ -deficiency in the medium. Sugars or amino acids did not interfere with uptake. Experimental conditions were optimized with regard to incubation medium, cell amount, cell age and length of preincubation. It is concluded that ileal cells of the guinea pig are superior to other experimental models for characterizing the ileal bile acid carrier, because they allow us to determine initial rates of uptake and have a very efficient energetic coupling.

Rats have been treated for 6 weeks with thioacetamide (0.1% in drinking water). The biochemical changes in liver microsomal metabolism of estradiol which are similar to those observed in human liver cirrhosis become already apparent after one week of treatment. These are diminishment of hepatic microsomal cytochromes P-450 and b5, comparable decrease of 2-hydroxylation and increase of formation of estrone from estradiol. The alterations of estrogen metabolism are reversible within two weeks after ending thioacetamide treatment. These data correspond to the already well established histological response of rat liver to thioacetamide, and its reversibility.