Glycerolipid biosynthesis in porcine adipose tissue in vitro: effect of adiposity and depot site.
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To compare genetic differences in glycerolipid biosynthesis, rates were determined in s.c. adipose tissue of lean and obese pigs at 28, 60 and 110 d of age. To compare depot-specific differences, glycerolipid biosynthetic rates were determined in outer s.c., middle s.c., perirenal and omental adipose tissues obtained from 105-kg contemporary pigs. Rates were determined with a 700 x g infranatant fraction of an adipose tissue homogenate by measuring glycerophosphate incorporation into total lipids (mostly phosphatidic acid) during 4 min. This assay represents entrance of substrates into the glycerolipid synthesis pathway or glycerophosphate acyltransferase (GPAT) activity. Rates measured for 60 min represent maximal synthesis of glycerolipid (more triacylglycerol than phosphatidic acid) or lipid synthesis capacity (LSC). Adipocyte diameter and volume were greater for adipose tissue of obese than of lean pigs both at 60 and 110 d. When expressed per cell, activity of GPAT and LSC were similar for lean and obese pigs at 28 d. At 60 d and 110 d, LSC was greater for obese than for lean pigs; GPAT activity was greater at 60 but not at 110 d in obese than in lean pigs. Expressed on a cell basis, GPAT activity was highest in omental and outer s.c., intermediate in perirenal and lowest in middle s.c. adipose tissue depots. Lipid synthesis capacity was highest in perirenal and lowest in outer and middle s.c. depots. Our results indicate that the LSC assay was more closely related to the accretion of fat in vivo than to GPAT activity.
