The effect of dibutyryladenosine 3′,5′‐monophosphate on the synthesis of bile salts in isolated hepatocytes from rat

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Abstract
The effect of dibutyryl cAMP (Bt2cAMP) on the synthesis of conjugated cholic, chenodeoxycholic and .beta.-muricholic acids was investigated. Hepatocytes were incubated with 1 mM Bt2cAMP for 3 h at 37.degree. C. In cells from rats with a basal rate of bile salt synthesis (soft-diet-fed rats) production of conjugated cholic acid was increased .apprx. 2-fold, synthesis of conjugated chenodeoxycholic acid was increased 10- to 20-fold but formation of its metabolite, conjugated .beta.2-muricholic acid, was decreased by 30-50% in the presence of the cyclic nucleotide. The sum of the amounts of the 3 bile salts produced (total bile salt synthesis) was increased 30-50% by Bt2cAMP. When hepatocytes were prepared from rats in which bile salt synthesis had been stimulated by feeding the bile salt sequestrant, cholestyramine, Bt2cAMP had no effect on conjugated cholic acid synthesis, increased conjugated chenodeoxycholic acid production 3-5 fold and decreased conjugated .beta.-muricholic acid synthesis by .apprx. 50%. Total bile salt synthesis was unchanged. The ratio of the amount of conjugated cholic acid to conjugated chenodeoxycholic acid + conjugated .beta.-muricholic acid produced, an indication of the activity of 7 .alpha.-hydroxycholest-4-en-3-one 12.alpha.-hydroxylase, was raised by Bt2cAMP in hepatocytes from soft-diet-fed but not in those from cholestyramine-fed rats. The effects of the cyclic nucleotide on the synthesis of the 3 bile salts in hepatocytes from soft-diet-fed rats were saturable at a concentration of .apprx. 2 mM. Responses were half-maximal at concentrations of Bt2cAMP varying between 0.5 and 1.5 mM. In hepatocytes from rats with a basal rate of bile salt synthesis Bt2cAMP probably has effects at 3 different stages in the pathway, at the level of cholesterol 7.alpha.-hydroxylase, 7.alpha.-hydroxycholest-4-en-3-one 12.alpha.-hydroxylase and chenodeoxycholic acid 6.beta.-hydroxylase. In cells from rats in which bile salt synthesis has been stimulated only the effect at the chenodeoxycholic acid 6.beta.-hydroxylase level is apparent. Bt2cGMP and Bt2cCMP had no effect on the synthesis of any of the bile salts measured, showing that the effects are specific for Bt2cAMP. The ratio of the amounts of the 3 bile salts inside the cells to those in the medium was decreased by .apprx. 90% when Bt2cAMP was present in the hepatocyte incubations. This effect was mimicked by Bt2cGMP and to a lesser extent by Bt2cCMP. Bt2cAMP has an effect on the uptake and/or secretion of bile salts in the hepatocytes.