In vivo determination of triglyceride secretion using radioactive glycerol in rats fed different dietary saturated fats.

Our objective was to determine the relative rates of in vivo triglyceride (TG) secretion and the composition of very low density lipoproteins (VLDL) in rats fed different dietary saturated fats. Male Sprague-Dawley rats (150-200 g) were fed diets containing 16% corn oil, or 14% butterfat, 14% beef tallow, 14% olive oil, or 14% coconut oil plus 2% corn oil for 5 wk. Changes in plasma TG specific radioactivity were determined in individual, unanesthetized fasted rats after injection of 100 microCi [2-3H]glycerol. Nonlinear regression analysis using a 2-compartment model was used to determine the fractional rate constant for TG turnover in plasma. The plasma TG pool was 33-40% larger with beef tallow than with corn, olive or coconut oil feeding (p less than 0.05), and 20% larger with beef tallow than with butterfat feeding. The rate of TG secretion into plasma (mg/min/100 g body weight) was 60% higher in animals fed beef tallow than corn or coconut oil (p less than 0.05) and 26-33% higher in animals fed beef tallow than olive oil or butterfat. Differences in VLDL composition (% wt) were also noted. Our data suggest that greater TG secretion is the primary factor contributing to the larger TG pool with ingestion of beef tallow relative to butterfat, corn or coconut oil. These results suggest that different dietary saturated fats have unique effects on TG metabolism in rats.