Changes in free fatty acids and triiodothyronine in response to feeding in pigs

Ten pigs were surgically implanted with jugular venous catheters. Blood samples were acquired before, during and after meals that occurred ad lib or after 5-hr or 17-hr fasts. 3,3',5-Triiodothyronine (T3) concentration increased (p less than 0.05) from 0.49 +/- 0.04 to 0.91 +/- 0.13 ng/ml (mean +/- SE) following feeding only when the pigs had been fasted for 17 hr prior to the meal. In contrast, free fatty acid levels decreased (p less than 0.05) with feeding under ad lib, 5-hr fasted and 17-hr fasted conditions. Free fatty acid concentration decreased from 222 +/- 66 mEq/l to 91 +/- 20 mEq/l (mean +/- SE) in pigs fed ad lib. Free fatty acids may function as hunger signals or their decrease may serve as a satiety signal in free-feeding animals. T3 may buffer against a large caloric intake associated with large meals, by increasing dietary thermogenesis.