The primary objective of this study was to document the effects of
starvation on
acylglycerol biosynthesis in homogenates of intramuscular and subcutaneous adipose tissues. Adipose tissue samples were obtained from 8th-13th thoracic rib sections from 12 Angus cattle (six steers plus six heifers). Three steers and three heifers were starved for 72 h prior to slaughter while the remainder were slaughtered 4 h after food was withheld. Fat-free 700 x g centrifugal fractions were used to measure 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 oleic, linoleic, or
alpha-linolenic acid. There were significant tissue x
fatty acid interactions for rates of incorporation into
diacylglycerols and
triacylglycerols; in subcutaneous, but not intramuscular homogenates, palmitic > stearic = oleic = linoleic =
alpha-linolenic acid. Subcutaneous homogenates incorporated a greater percentage of G-3-P into
triacylglycerols, and a lesser percentage into
phospholipid, than intramuscular homogenates (P < 0.05). In intramuscular homogenates, the primary product of G-3-P esterification to
saturated fatty acids was
phospholipids. When
unsaturated fatty acid served as substrates,
triacylglycerols and
phospholipids were produced in equal proportions in intramuscular homogenates, and
triacylglycerols were the predominant product in subcutaneous homogenates. Intramuscular adipose tissue homogenates exhibited no response to
starvation, whereas
triacylglycerol and
diacylglycerol synthesis was depressed by approximately 50% in subcutaneous adipose tissue homogenates. Similarly, phosphatidic
phosphohydrolase activity, initially greater in subcutaneous than in intramuscular adipose tissue, was decreased by approximately 50% by
starvation in subcutaneous adipose tissue, but not in intramuscular adipose tissue. We conclude that differences in rates of
diacylglycerol and
triacylglycerol biosynthesis, and response to
starvation, between intramuscular and subcutaneous adipose tissues were due to dissimilarities in the activity of phosphatidic
phosphohydrolase.