Inhibition of triglyceride synthesis in everted intestinal sacs

Interactions between medium-chain and long-chain triacylglycerols in lipid and energy metabolism in growing chicks

The combined effects of dietary medium-chain triacylglycerols (MCT) and long-chain triacylglycerols (LCT) on lipid and energy utilization in chicks were investigated. Corn oil was used as the LCT source, and trioctanoin (8:0) was used as the MCT source. The efficiency of dietary energy utilization (such as metabolizable energy values and fat and energy retention) decreased linearly as the level of MCT increased, but the efficiency of dietary protein utilization (protein retained per protein consumed) was not affected in a consistent manner. Fecal saturated and monounsaturated fatty acid composition was dependent on the dietary fatty acid composition, whereas fecal linoleic acid content was not. It is concluded that dietary MCT and LCT influence each other to some degree, with respect to protein and lipid metabolism in chicks. Moreover, in most cases, the nutritional characteristics of each triacylglycerol, including food efficiency and fat and energy retention, are independent of each other in growing chicks.

Inhibition of steady-state intestinal absorption of long-chain triglyceride by medium-chain triglyceride in the unanesthetized rat

Maximal steady-state intestinal absorption rates in unanesthetized rats for triolein, a long-chain triglyceride, and for trioctanoin, a medium-chain triglyceride, are known to differ. Both these lipids are hydrolyzed in the intestinal lumen but the products of hydrolysis are metabolized differently by the mucosal cell. Intraduodenal infusion of trioctanoin was found to reduce steady-state triolein absorption. Luminal lipolysis was shown not to be rate-controlling. High rates of trioctanoin infusion significantly lowered the pH of the luminal aqueous phase and altered the partition of oleic acid between aqueous and oil phases. Two possible mechanisms for the inhibition of triolein uptake are considered. In the intestinal lumen medium chain lipids might have lowered the activity of oleic acid monomers in the aqueous phase and reduced passive diffusion into mucosal cells. Alternatively, competition between long and medium chain fatty acids for some common receptor during transport into the intestinal mucosal cell may have occurred. Despite significant inhibition of triolein absorption by high levels of trioctanoin, the maximum number of calories absorbed from mixtures of triglycerides exceeded the maxima from either glyceride alone. The optimum proportion of triolein to trioctanoin in lipid infusion mixtures was about 3:4 by weight and the optimum dosages about half maximal for each triglyceride, which represented a caloric intake of 4 kcal/rat per 2 hr. The absorption coefficient for this lipid mixture was about 90%. It is suggested that in patients who have a limited intestinal absorptive capacity dietary fat intake might be doubled with a caloric supplement of medium-chain triglycerides without increase in steatorrhea of long-chain fat.