👤 K Sonoyama

An intravenous infusion of hexamethonium, a ganglionic blocker, did not affect the increase in the apolipoprotein A-IV mRNA level in the residual ileum following a massive small bowel resection in unrestrained conscious rats. The result suggests that upregulation of the apolipoprotein A-IV gene in the residual ileum is not mediated by a neural pathway, including the nicotinic synapse route. Show less

The effect of peptide YY, a gastrointestinal hormone, on the expression of the apolipoprotein A-IV gene in the intestinal epithelial cell line Caco-2 was examined by semiquantitative RT-PCR followed by Southern hybridization with an inner oligonucleotide probe. Apolipoprotein A-IV mRNA levels were increased in response to peptide YY in a dose- and time-dependent fashion. Western blotting revealed that the exogenous peptide YY increased the intracellular concentration of apolipoprotein A-IV. In contrast, apolipoprotein A-I, B, and C-III mRNA did not respond to peptide YY. Differentiated Caco-2 cells expressed Y1- but not Y2- and Y5-receptor subtype mRNA. The present results suggest that peptide YY modulates apolipoprotein A-IV gene expression, likely via the Y1-receptor subtype in intestinal epithelial cells. Show less

To clarify the role of neural factors in the regulation of apolipoprotein (apo) A-IV expression in the small intestine, we investigated the effect of neural blockers on mRNA levels of apo A-IV in rat small intestine. Either ganglionic blocker (hexamethonium), cholinergic blocker (atropine) or beta-adrenergic blocker (propranolol) was infused intravenously to unrestrained conscious rats for 8 h, and then total RNA was isolated from the small intestine and analyzed using Northern hybridization. Apo A-IV mRNA levels in the ileum were significantly lower in hexamethonium- or atropine-infused rats than in saline- (control) or propranolol-infused rats. Immunoblot analysis showed no difference in plasma apo A-IV concentrations between hexamethonium- and saline-infused groups. The lower mRNA levels of apo A-IV in the ileum of hexamethonium-infused rats were observed even in bile-drained rats, indicating that the lower expression was not due to any changes in bile availability. The ileal apo A-IV mRNA levels were significantly higher in rats infused with lipid emulsion into the ileum than in rats infused with glucose-saline, and the concomitant infusion of intravenous hexamethonium did not affect the higher levels of apo A-IV mRNA. These results suggest that the basal expression of the ileal A-IV gene is at least partially regulated in a site-specific manner by cholinergic neurons. Show less

Gene expression of activin, activin receptors, and follistatin was investigated in vivo and in vitro using semiquantitative RT-PCR in intestinal epithelial cells. Rat jejunum and the intestinal epithelial cell line IEC-6 expressed mRNA encoding the betaA-subunit of activin, alpha-subunit of inhibin, activin receptors IB and IIA, and follistatin. An epithelial cell isolation study focused along the crypt-villus axis in rat jejunum showed that betaA mRNA levels were eight- to tenfold higher in villus cells than in crypt cells. Immunohistochemistry revealed the expression of activin A in upper villus cells. The human intestinal cell line Caco-2 was used as a differentiation model of enterocytes. Four- to fivefold induction of betaA mRNA was observed in postconfluent Caco-2 cells grown on filter but not in those cells grown on plastic. In contrast, follistatin mRNA was seen to be reduced after reaching confluence. Exogenous activin A dose-dependently suppressed the proliferation and stimulated the expression of apolipoprotein A-IV gene, a differentiation marker, in IEC-6 cells. These results suggest that the activin system is involved in the regulation of such cellular functions as proliferation and differentiation in intestinal epithelial cells. Show less