Adipose tissue lipid metabolism during pregnancy and lactation

Abstract

1. The effect of pregnancy and lactation on some aspects of adipose tissue lipid metabolism in rat and mouse was studied. An attempt was made to elucidate control mechanisms for the changes in adipose tissue lipoprotein lipase activity in the rat during pregnancy and lactation. 2. Oxidation of glucose and synthesis of fatty acids from glucose by rat adipose tissue was either normal or elevated during early- and mid-pregnancy. Late pregnancy and lactation were characterized by low rates of glucose oxidation and fatty acid synthesis. 3. Rat adipose tissue lipoprotein lipase activity fell during early-pregnancy, prior to a recovery of enzyme activity in mid-pregnancy. The enzyme activity fell during late pregnancy to very low levels which were maintained until at least day 8 of lactation. Lipoprotein lipase activity in mouse adipose tissue fell during early-pregnancy and this low level of activity was maintained until day 17 of pregnancy, when an increase in activity occurred. The increased activity was maintained in early-lactation. 4. The response of rat adipose tissue in vitro to epinephrine stimulation in the release of FFA and glycerol was increased throughout pregnancy and early-lactation. Release of both FFA and glycerol was depressed on day 10 of lactation. Basal release of PPA increased but not significantly on days 7 and 12 of pregnancy and 3 of lactation. Glycerol release was elevated on day 12 of pregnancy and day 3 of lactation. Evidence is presented that the rate of FFA reesterification in the rat is decreased in early-to mid-pregnancy and increased in late pregnancy. Basal FFA and glycerol release in mouse adipose tissue in vitro were not significantly different from controls during pregnancy. FFA release was depressed on day 2 of lactation whereas glycerol release was increased. Both FFA and glycerol release in response to epinephrine stimulation increased, but not significantly, in late-pregnancy and markedly increased in early lactation. Prolactin injections had no significant effect on virgin rat adipose tissue lipoprotein lipase activity in vivo. Oestradiol benzoate markedly depressed lipoprotein lipase activity in virgin rat adipose tissue in vivo, and simultaneous administration of oestradiol benzoate plus prolactin did not decrease enzyme activity further. Simultaneous administration of oestradiol benzoate and a-ergocryptine produced a significant decrease in lipoprotein lipase activity in virgin rat adipose tissue in vivo. a-Ergocryptine administration to lactating rats reduced litter weight gain and increased the activity of lipoprotein lipase in adipose tissue in vivo.