Ontogenic regulation of components of ileal bile acid absorption

The apical sodium-dependent bile acid cotransporter (ASBT) and the ileal bi le acid binding protein (IBABP) are two components of ileal bile acid absor ption. During the third postnatal week of the rat, there is a dramatic incr ease in ASBT and IBABP expression. The goals of this study were to examine the role of hormones on the ontogenic expression of ASBT mRNA and the role of weaning for both ASBT and IBABP mRNA. Administration of various doses of dexamethasone during the second postnatal week induced ASBT mRNA levels, a nd this effect was significantly increased with concomitant thyroxine treat ment. Early weaning and weaning prevention were utilized to investigate the influence of dietary factors. ASBT and IBABP mRNA levels were significantl y elevated by early weaning and were decreased by weaning prevention compar ed with littermate controls. Thus, glucocorticoids and thyroxine appear to play a role in the ontogenic expression of ASBT mRNA and weaning appears to participate in both ASBT and IBABP expression.