Diet, pregnancy, and lactation: effects on adipose tissue, lipoprotein lipase, and fat cell size

Adipose tissue fat cell size and lipoprotein lipase (LPL) activity were determined in the retroperitoneal and subscapular depots of nonpregnant, pregnant, and postpartum rats fed either a standard laboratory diet or a high-fat diet containing 55% fat by weight. High-fat feeding for 20 days increased, in nonpregnant rats, fat cell size and LPL activity two- to threefold in both depots. In pregnant rats at term, fat cell size was increased and LPL activity was depressed in both dietary groups. Twenty days postpartum, both retroperitoneal fat cell size and LPL activity were decreased in proportion to the size of the litter. Rats not allowed to lactate had fat cell sizes and LPL activity that were not significantly different than in nonpregnant controls. Fat cell size and LPL activity in rats nursing four pups were reduced to 77% and 36% of control, respectively. Those nursing a normal-sized litter of eight pups demonstrated a further reduction of fat cell size to 38% and of LPL activity to 2% of nonpregnant control values. High-fat feeding and obesity did not prevent the fat loss and decreased LPL activity associated with lactation; fat cell size was decreased to 61% and LPL activity to 3% of control values. Values for the subscapular depot followed essentially the same pattern as that observed for the retroperitoneal depot. Mammary LPL activity was increased more than tenfold in animals nursing four or eight pups compared with values at term, whereas no activity was detected in rats not allowed to lactate.