Repression of fat-dependent intestinal apo A-IV mRNA abundance by medium chain triacylglycerols and proteins, and elevation by carbohydrates of fat-dependent apo A-IV transport in suckling rat pups.

Nutrients regulating intestinal apo A-IV synthesis and secretion in developing rats have not been clearly defined. We examined the effect of ingestion of fats, carbohydrates and proteins on the abundance of intestinal apo A-IV mRNA and the serum concentration of apo A-IV in 14-day-old suckling rat pups fasted overnight. In pups ingesting long-chain fatty acid-fat (soybean oil, triolein: LCT), there was a prompt elevation of the mRNA at 1.5 h after ingestion, although a graded dose of soybean oil did not result in a comparable elevation of the apo A-IV mRNA. In pups on MCT, but not trilaurin, there was a repression of the LCT-dependent elevation of the message. In pups on Intralipid (composed of soybean oil, lecithin and glycerol), mRNA was elevated at 6 h after ingestion. Administration of Intralipid with lactose, glucose, fructose and sucrose induced a rapid elevation of mRNA together with elevation of serum apo A-IV, although administration of casein, whey proteins and soybean proteins resulted in repression of the Intralipid-dependent mRNA elevation. The message correlated weakly to the serum apo A-IV and triacylglycerols and with no correlation to intestinal fat accumulation. These results suggest that metabolic events following the ingestion of milk components modulate intestinal apo A-IV expression in developing rats, possibly through mucosal fatty acid utilization.