Lipoprotein lipase transport in plasma: role of muscle and adipose tissuesin regulation of plasma lipoprotein lipase concentrations

Lipoprotein lipase (LPL) is synthesized in tissues involved in fatty acid m etabolism such as muscle and adipose tissue. LPL is also found in the circu lation, but is mostly lipolytically inactive. The proportion of active circ ulating LPL increases after a fatty meal. We investigated the release of ac tive and inactive LPL from adipose tissue and muscle in the fasting and pos tprandial states. Arteriovenous concentration gradients of LPL across adipo se tissue and forearm muscle were measured in male subjects before and afte r a fat-rich meal (n = 7) and before and during infusion of a triacylglycer ol emulsion (Intralipid) (n = 6), Plasma LPL activity rose after the meal a nd more so during Intralipid infusion. Plasma LPL mass (>95% inactive LPL) increased after the meal but decreased after Intralipid infusion. In the fa sting state (n = 13) muscle efflux of LPL activity was 0.263 +/- 0.098 mU/m in per 100 ml of muscle tissue whereas there was an influx of LPL activity to adipose tissue of 0.085 +/- 0.100 mU/min per 100 g of adipose tissue (P < 0.02 muscle vs. adipose tissue). Similarly in the postprandial state only muscle released LPL activity. Both tissues released LPL mass, In the fasti ng state efflux was 17.8 +/- 8.8 ng/min per 100 mi muscle and 55.2 +/- 21.3 ng/min per 100 g of adipose tissue (P < 0.05 muscle vs. adipose tissue). R elease of LPL, either active or inactive, was not correlated with levels of nonesterified fatty acids or plasma triacylglycerol. In conclusion, there is a substantial release of LPL from adipose tissue and muscle, most of whi ch is inactive, A small proportion of active LPL seems to be redistributed from muscle to adipose tissue.