Importance of muscle lipoprotein lipase in rats during suckling

Abstract

In order to evaluate the relative importance of groups of tissues containing lipoprotein lipase (LPL) in the removal of serum triacylglycerols during development, LPL activity was determined in cardiac and skeletal muscle, brown (BAT) and white adipose tissue (WAT), lung and kidney of rats aged 0-60 days, either fed or fasted for 6 h. On fasting, LPL activity did not change in lung and kidney, decreased in WAT except at 14 days and to a lesser extent in BAT, whereas muscle LPL decreased at 0, 3, and 7 days and increased from 14 days onward. The fasting-induced changes in serum triacylglycerol concentrations in suckling pups could be attributed to corresponding changes in muscle LPL. In the adult, the main contributor to total LPL activity was WAT in fed rats and muscle in fasted rats, as expected. In suckling pups, however, muscle LPL contributed 63-85% of the total and WAT less than 25%, whatever the nutritional state. The results strongly suggest that clearing of circulating chylomicrons during suckling largely depends on muscle LPL.

Fatty acid oxidation and ketogenesis during development

“…Whereas long-chain fatty acids are absorbed from the small intestine as chylomicrons, medium-chain fatty acids are absorbed from the stomach as free acids (Hamosh, 1979 ;Fernando-Warnakulasuriya et al, 1981 ;Aw and Grigor, 1980) and, as such, are excellent oxidative substrates for neonatal tissues, particularly for the liver (Frost and Wells, 19811. In rats, a large rise in plasma NEFA and triglyceride occurs a few hours after birth with the onset of suckling, and plasma NEFA and triglyceride levels remain very high throughout the suckling period, decreasing after weaning (Page, Krebs and Williamson, 1971 ;Dahlquist, Persson and Persson, 1972 ;Foster and Bailey, 1976a ;Planche et al, 1980). The capacity of extra-hepatic tissue to take up plasma triglycerides increases during the suckling period in rats.…”

“…The capacity of extra-hepatic tissue to take up plasma triglycerides increases during the suckling period in rats. The lipoprotein lipase activity of heart, skeletal muscles and brown adipose tissue (BAT) emerges substantially during the first 24 h after birth (Cryer and Jones, 1978) and remains elevated during the suckling period (Cryer and Jones, 1978 ;Planche et al, 1980). The NEFA released by the hydrolysis of plasma triglycerides are thus directly available as fuel for the extra-hepatic tissues.…”

Lipoprotein lipase and the uptake of lipids by adipose cells during development

“…The decline in adipose tissue lipoprotein lipase activities during the second half of suckling are less easily related to the aspects of cellularity and lipid accretion just discussed. In the first case the total lipid content of most depots continue to increase over this period (Cryer and Jones, 1979b) and pad growth continues (Cryer and Jones, 1979b ;Planche et al, 1980) as does adipocyte cell size although adipocyte numbers do not alter substantially (Cryer and Jones, 1979b Jones, 1978 ;Planche et al, 1980). Following weaning in the rat average adipocyte size increases substantially in a fashion which is related to the activity of lipoprotein lipase expressed on a per cell basis (Hietanen and Greenwood, 1977) (Vannier et al, 1982 ;Al-Jafari and Cryer, 1984 …”

“…In the case of the rat lung, lipoprotein lipase activity has been detected up to 5 days before birth and increases substantially during the last few hours in utero and during the first day of extrauterine life Cryer and Jones, 1978a ;Hietanen and Hartiala, 1979 ;Planche et al, 1980). The enzyme activity is elevated therefore during the period of lung development when rapid rates of pulmonary surfactant synthesis occur (Farrell and Hamosh, 1978) and it has been suggested that the increased perinatal pulmonary lipoprotein lipase activity may provide a source of diglyceride for the dipalmitylphosphatidylcholine production necessary for pulmonary surfactant formation (Cryer and Jones, 1978a ;Weinhold et al, 1980 (Glatz and Veerkamp, 1982 (Tan et al, 1977) or mice (Rath et al, 1974 Nedergaard and Lindberg, 1982).…”

Effect of Heparin on Serum and Tissue Lipases in the Developing Rat

“…The pattern of change in tissue enzyme content was similar for heart and lung, but different from hepatic lipase. LPL activity in the former increased from 10 and 30% to 60 and 100% of adult values between birth and 10 days while in the latter enzyme activity exceeded adult levels at birth and decreased to 50% of adult values during the latter half of the suckling period (days [10][11][12][13][14][15][16][17][18][19][20][21] isolated organs or intact animals, have shown that the easily accessible endothelial enzyme is directly related to triglyceride hydrolysis; its removal from the endothelium following heparin infusion completely abolishes the ability of isolated organs to hydrolyze infused lipoprotein-triglyceride (9, 21), whereas injection of antibodies against lipoprotein lipase is rapidly followed by marked hyperlipemia (1, 16). Thus, serum postheparin lipolytic activity provides an accurate measure of functional (endothelial) lipase concentrations.…”