Human adipose tissue lipoprotein lipase: changes with feeding and relation to postheparin plasma enzyme
Iverius, P.H.; Brunzell, J.D.
American Journal of Physiology 249(1 Pt 1): E107-E114
1985
ISSN/ISBN: 0002-9513 PMID: 4014455 Document Number: 242359
An assay procedure using 3 different methods to recover lipoprotein lipase (LPL) activity from biopsy specimens of human adipose tissue was developed. Elution of enzyme from small pieces of tissue was performed at 4 and 37.degree. C using a physiological buffer containing heparin and serum. Extraction of enzyme from a tissue homogenate was carried out in the presence of detergent (sodium deoxycholate and Nonidet P-40), which markedly improved the recovery of enzyme activity. Elution at 4.degree. C represents extracellular enzyme activity only and therefore theoretically is the closest measure of physiologically active LPL on vascular endothelium, whereas elution at 37.degree. C reflects some intracellular enzyme secreted during the incubation period. In female subjects of various relative body weights activity eluted at 37.degree. C as well as detergent-extracted activity were highly correlated with the extracellular activity eluted at 4.degree. C (r = 0.9). All 3 parameters correlated strongly with LPL activity in postheparin plasma, suggesting that they are valid indices of physiologically active LPL. The regression of LPL activity in plasma after a 60-min heparin infusion on adipose tissue LPL yielded higher correlation coefficients for activities recorded after elution at 4 and 37.degree. C (r = 0.725 and 0.754, respectively) than for detergent extraction (r = 0.607). The increment of adipose tissue LPL after feeding was approximately twice as high for the activity eluted at 4 and 37.degree. C (34%) as for detergent-extracted activity (19%). LPL activity eluted from adipose tissue biopsy specimens with serum and heparin at 4 or 37.degree. C are better indices of physiologically active enzyme than total tissue activity, presumably because the former parameters mainly reflect extracellular enzyme.