This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Elevated postabsorptive and postprandial plasma triglyceride (TG) concentrations are associated with increased cardiovascular disease (CVD). This suggest that total plasma TG load (24-hour plasma TG concentration) is an important risk factor for CVD. Although exercise is associated with decreased CVD, its effect on plasma TG concentration and metabolism is not clear. 1) Data from studies investigating the effects of exercise on postabsorptive plasma TG concentration are conflicting. 2) There is good evidence that exercise lowers the rise in plasma TG concentration after consumption of a single high-fat test meal. However, the effects of exercise on postprandial plasma TG concentration after ingestion of a typical mixed meal are largely unknown, and the effects of exercise on 24-hour plasma TG concentration has never been studied. 3) The mechanisms responsible for the postprandial TG-lowering effect of exercise remain unclear. The primary objectives of this proposal are to evaluate the effects of exercise on 24-hour plasma TG concentration, and to determine potential metabolic mechanisms responsible for the exercise-induced changes in plasma TG concentration. We hypothesize that: 1) Exercise decreases total 24-hour plasma TG concentration, predominately by lowering plasma TG concentration after meals, 2) Exercise in the morning has a greater effect on total 24-hour plasma TG concentration than exercise performed in the evening, and 3) The exercise-induced decrease in postprandial plasma TG concentration is, at least in part, due to lower hepatic VLDL-TG secretion during postprandial hyperinsulinemia. To test our hypothesis we will measure plasma TG concentration every hour for 24 hours and measure hepatic VLDL-TG secretion (by using stable isotope labeled tracer techniques) during hyperinsulinemia in subjects with increased plasma TG concentrations after rest and exercise. The data generated from concenration the proposed studies will improve our understanding of the metabolic control of plasma TG concentration. Furthermore, they will help establish appropriate guidelines to lower plasma TG concentration via physical activity.