Abstract
The studies reported here evaluated the role of acute lipid feeding and dietary lipid profiles in the regulation of intestinal apolipoprotein B-48 synthesis and secretion using the rat model. Acute fat loading, in vitro and in vivo, resulted in a 2 to 2. 5 fold increase in apolipoprotein B content of both jejunal enterocytes and mucosal scrapings. A 40 day period of dietary manipulation (fat saturation and quantity) showed a significant increase in apolipoprotein B-48 content of fasted jejunal enterocytes, but not fasted mucosal scrapings when dietary fat energy was increased from 5% to 20%. Manipulation of dietary fat saturation was without effect upon apolipoprotein B-48 content of fasted jejunal enterocytes and mucosal scrapings. Chronic change of dietary fat saturation showed no effect upon TAG-rich lipoprotein particle size in the mesenteric lymph duct in response to isoenergetic fat loads. However, a 20% sunflower oil (PUFA rich) diet administered for 40 days was found to be associated with reduced blood total cholesterol concentration; and coconut oil (SFA rich) diet was associated with raised total blood cholesterol concentration. Our study suggests that increased transport of fat, during absorption of a dietary fat load, is accommodated principally by increased size (about 4 fold) of TAG-rich lipoprotein particles with only a small increase in particle number (about 1. 45-1. 6 fold). Dietary fat saturation showed no effect upon the mass of apolipoprotein B-48 secreted during the studied period of lipid absorption. However, the average size of the triacylglycerol-rich lipoprotein particles, estimated using the lymph apolipoprotein B-48/triacylglycerol ratio, appears to increase with increased rate of triacylglycerol transport and chain length of ingested fatty acids A final study was conducted to assess the effects of a fat load upon the average size of the triacylglycerol-rich lipoprotein particles secreted into the mesenteric lymph duct of rats receiving exogenous insulin over a 40 day period. Triacylglycerol-rich lipoprotein particle size during peak lipid absorption was unaffected by chronic insulin administration.