Ontogenic and glucocorticoid-accelerated expression of rat 14 kDa bile acid-binding protein

Abstract

Background A 14 kDa protein is a major rat ileal cytosolic bile acid‐binding protein (14 kDa I‐BABP). This report describes the normal and glucocorticoid‐accelerated postnatal expression of 14 kDa I‐BABP. Methods 14 kDa I‐BABP and its mRNA were detected by antiserum and antisense cRNA probe, respectively, in ileum and ovary from 7‐, 14‐, 21‐, 28‐, and 35‐day‐old rats. Results A positive histochemical reaction with 14 kDa I‐BABP antiserum was found in cytosol of ileal enterocytes and ovarian luteal cells at 21 and 35 days of age, respectively. Likewise, Northern blot analysis indicated that the cRNA probe hybridized to a single transcript of 500 bp in total cellular RNA prepared from the ileum of 21‐day‐old and ovary of 35‐day‐old rats. Corticosteroid treatment resulted in a histochemical reaction in ileum of 14‐day‐old animals as compared to the appearance of this reaction in 21‐day‐old control littermates. Similarly, Northern blot analysis detected the earlier appearance of mRNA levels in corticosteroid‐treated animals (11 days vs. 17 days in control animals). Conclusions 14 kDa I‐BABP and its mRNA are normally expressed in rat ileum at 17 days of postnatal life. 14 kDa I‐BABP is expressed considerably later in rat ovary. Corticosteroid treatment results in precocious expression of ileal 14 kDa I‐BABP. © 1996 Wiley‐Liss, Inc.

Hormonal regulation of expression of ileal bile acid binding protein in suckling rats

“…The developmental pattern of rat IBABP mRNA expression is one in which there is little or no mRNA during the suckling period, with a dramatic increase occurring in the third postnatal week. Because prior studies had shown only a single value for IBABP mRNA at each age (8,14,39), to set the stage for our hormonal studies we thought that it was important to assess the animal-to-animal variation and to include statistical analysis of the developmental rise. Figure 1 shows that after a 5-h exposure of the autoradiogram, IBABP mRNA was first detectable on postnatal day 19.…”

“…IBABP mRNA is one of the most abundant transcripts of the ileal mucosa. Although expressed only in the villus epithelial cells (8,14,27), the mRNA shows a strong signal on Northern blots of total RNA prepared from the intact ileum (i.e., full thickness of muscle plus mucosa). Typical autoradiographs of such blots show that in adult rats the IBABP mRNA signal is detectable after less than 1 h of exposure.…”

“…changes of the transporter and the binding protein is that the onset of active absorption of bile acids in the rat ileum occurs during this time period (3,5,35,43). Although there are several studies on the ontogenic regulation of the overall process of bile acid transport (2,24,25,42), the regulation of its components such as IBABP has received little attention (14,16). Such regulation is in turn an important aspect of the maturation of the enterohepatic circulation of bile acids (26).…”

“…Because these surges of both corticosterone and thyroxine begin before the detection of a significant increase in IBABP mRNA levels, they are logical candidates in regulating IBABP mRNA expression. To date it is apparent that pharmacological doses of glucocorticoid can elicit precocious induction of IBABP mRNA (14,16). However, there have been no studies with lower glucocorticoid doses in the physiological range.…”

Diethyl Pyrocarbonate Is an Inhibitor of Cardiac, Intestinal and Renal Ecto-ATPase.

“…It was postulated that in mammalian cardiac muscle ecto-ATPase participates in both signal transduction and adenosine recycling [10]. Intestinal ecto-ATPase presumably functions as a bile acid-binding protein [6]. In kidney, the enzyme is involved in the regulation of cell-cell interactions at the level of microvilli of proximal convoluted tubules mediated by ATP/ADP [171.…”