STARVATION DEPRESSES ACYLGLYCEROL BIOSYNTHESIS IN BOVINE SUBCUTANEOUSBUT NOT INTRAMUSCULAR ADIPOSE-TISSUE HOMOGENATES

The primary objective of this study was to document the effects of sta rvation on acylglycerol biosynthesis in homogenates of intramuscular a nd subcutaneous adipose tissues. Adipose tissue samples were obtained from 8th-13th thoracic rib sections from 12 Angus cattle (six steers p lus six heifers). Three steers and three heifers were starved for 72 h prior to slaughter while the remainder were slaughtered 4 h after foo d was withheld. Fat-free 700 x g centrifugal fractions were. used to m easure the esterification of radiolabeled sn-glycerol 3-phosphate (G-3 -P) into acylglycerols at 1.0 mM palmitic or stearic acid, or 0.2 mM o leic, linoleic, or alpha-linolenic acid. There were significant tissue x fatty acid interactions for rates of incorporation into diacylglyce rols and triacylglycerols; in subcutaneous, but not intramuscular homo genates, palmitic > stearic = oleic = linoleic = alpha-linolenic acid. Subcutaneous homogenates incorporated a greater percentage of G-3-P i nto triacylglycerols, and a lesser percentage into phospholipid, than intramuscular homogenates (P < 0.05). In intramuscular homogenates, th e primary product of G-3-P esterification to saturated fatty acids was phospholipids. When unsaturated fatty acid served as substrates, tria cyglycerols and phospholipids were produced in equal proportions in in tramuscular homogenates, and triacylglycerols were the predominant pro duct in subcutaneous homogenates. Intramuscular adipose tissue homogen ates exhibited no response to starvation, whereas triacylglycerol and diacylglycerol synthesis was depressed by approximately 50% in subcuta neous adipose tissue homogenates. Similarly, phosphatidic phosphohydro lase activity, initially greater in subcutaneous than in intramuscular adipose tissue, was decreased by approximately 50% by starvation in s ubcutaneous adipose tissue, but not in intramuscular adipose tissue. W e conclude that differences in rates of diacylglycerol and triacylglyc erol biosynthesis, and response to starvation, between intramuscular a nd subcutaneous adipose tissues were due to dissimilarities in the act ivity of phosphatidic phosphohydrolase. (C) 1998 Elsevier Science Inc. All rights reserved.