One cycle of reproduction consisting of pregnancy, lactation or no lactation, and recovery: effects on fat pad cellularity in ad libitum-fed and food-restricted rats.

Groups of nine ad libitum-fed and food-restricted Osborne-Mendel rats, weighing between 200 and 220 g at mating, were killed on day 21 of pregnancy, day 21 of lactation and day 21 of a postweaning recovery period. Food-restricted rats were fed 70% of the mean daily ad libitum intake. Groups of nine ad libitum-fed animals, not permitted to suckle their young, were also killed on day 21 and day 42 postpartum. Groups of nine nonpregnant rats of comparable body weight on day 0 were killed on day 0, day 21, day 43 and day 64 of the experiment to serve as age and growth controls. At the time of death, subscapular, parametrial and retroperitoneal fat pads were dissected, weighed and sampled for determination of fat cell size and fat cell number. At 21 days postpartum, animals that had gone through pregnancy but did not lactate exhibited increased fat pad weight and significantly increased fat cell number in the parametrial and retroperitoneal depots although not in the subscapular depot. This increase in fat cell number was still evident 42 days postpartum and may predispose these animals to subsequent obesity.