Tissue-specific regulation of lipoprotein lipase in humans: effects of fasting.

ABSTRACT

BACKGROUND: We have previously reported that the activity of lipoprotein lipase (LPL) measured in postheparin plasma from humans fasted for 30 h is increased relative to the fed state. This is in contrast to laboratory animals, where the strong down-regulation of LPL in their adipose tissue on fasting is reflected in decreased levels of LPL activity in postheparin plasma. MATERIALS AND METHODS: To search for the tissue source of the increase in LPL activity on fasting of humans, young, healthy subjects were fasted for 10, 20 or 30 h, and LPL was measured in plasma (pre- and postheparin) and in biopsies from subcutaneous adipose tissue (abdominal) and from a skeletal muscle (tibialis anterior). Both LPL activity and LPL protein mass were measured in the tissue homogenates. Values after fasting were compared with values from postprandial samples obtained 2 h after a meal. RESULTS: Fasting for up to 30 h did not alter LPL activity in basal plasma (preheparin). LPL activity in postheparin plasma remained unchanged after 10 and 20 h of fasting, but was increased by 50% after 30 h (P < 0.05). Ten hours of fasting caused a 25% (P < 0.05) decrease in LPL activity in subcutaneous adipose tissue, while LPL activity in skeletal muscle remained unchanged. After 30 h of fasting, both LPL activity and mass had decreased by approximately 50% (P < 0.05) in adipose tissue, but had increased by approximately 100% (P < 0.05) in muscle. CONCLUSIONS: The increase in postheparin plasma LPL activity after 30 h of total food deprivation of healthy human subjects seemed to reflect an increased activity and mass of LPL in skeletal muscle.