Intravenous infusion of hexamethonium and atropine but not propranolol diminishes apolipoprotein A-IV gene expression in rat ileum

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 g anglionic blocker (hexamethonium), cholinergic blocker (atropine) or beta-a drenergic blocker (propranolol) was infused intravenously to unrestrained c onscious rats for 8 h, and then total RNA was isolated from the small intes tine 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 hexamethoniu m- and saline-infused groups. The lower mRNA levels of apo A-IV in the ileu m of hexamethonium-infused rats were observed even in bile-drained rats, in dicating that the lower expression was not due to any changes in bile avail ability. The ileal apo A-IV mRNA levels were significantly higher in rats i nfused 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 b asal expression of the ileal A-IV gene is at least partially regulated in a site-specific manner by cholinergic neurons.