A Comparison of the Tissue Distribution and Metabolism of ll-Deoxy-[l,2-3H]Corticosterone in the BALB/c and C57BL/6 Strains of Mice*

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Abstract
Corticosteroid side-chain isomerase of mouse liver catalyzes the reversible interconversion of the ketol and aldol configurations of the corticosteroid side chain. Activity of the enzyme is under genetic control. To see if the differences in activity that were observed in vitro between inbred strains of mice were also expressed in vivo, the metabolism of 11-deoxy-[1,2-3H]corticosterone ([1,2-3H]DOC) was studied in BALB/c (C) and C57BL/6 (B6) mice. Maximum radioactivity appeared in most organs within 5-10 min after i.p. injection. Uptake of tracer into liver was greater for C than B6 mice. Tritium levels in blood, kidney, and pancreas were higher in C mice; levels in adrenal, abdominal fat, and mesentery were higher in B6 mice. In both strains, the concentrations of tracer in tissues, except in gastrointestinal tract, declined and reached a minimum within 60 min. Most of the radioactivity (84%) from [1,2-3H]DOC accumulated in the lumen of the intestinal tract, and few counts were found in the wall. Intestinal concentrations of 3H at different postinjection intervals were greater for B6 than C mice. In contrast, twice as much radioactivity appeared in the kidneys of C than of B6 mice. The organs of excretion (kidney, liver, gall bladder and intestine) concentrated steroid from blood. Heart striated muscle, and spleen excluded steroid. Four acidic metabolites of [1,2-3H]DOC were detected in liver, and 2 were detected in small intestine. Acids formed in liver did not accumulate, and no differences between C and B6 strains were seen. More acid metabolites accumulated in intestines of C mice than in those of B6 mice. The quantitative aspects of steroid acid formation in vivo are consistent with previous in vitro findings that livers from C mice synthesize more pregnolic acid from DOC than do livers from B6 mice.