Size and number of adipocytes in the perinephric fat during pregnancy and the postpartum period in rats

Adipose tissue metabolism during early pregnancy in the rat: temporal relationships of changes in the metabolic activity, number of insulin receptors, and serum hormone concentrations

The temporal relationships between changes in rates of fatty acid and acylglycerol glycerol synthesis; the activity of lipoprotein lipase of parametrial adipocytes and their capacity to bind insulin; and the serum concentrations of insulin, progesterone, prolactin, and total lactogenic activity have been examined in rats during the first 15 days of pregnancy. The rate of fatty acid and acylglycerol synthesis showed a transient increase at Days 9 and 12 of pregnancy, whereas there was no change in the activity of lipoprotein lipase activity except for a fall between Days 12 and 15 of pregnancy. The capacity of adipocytes to bind insulin was increased by Day 6 of pregnancy and remained elevated until at least Day 15; no changes in the affinity for insulin were observed. Serum progesterone, insulin, and total lactogenic activity were elevated by Days 3, 9, and 12 of pregnancy, respectively. The results show that progesterone but not placental lactogen could be responsible for the rise in the insulin-binding capacity of rat adipocytes during pregnancy, whereas the fall in lipogenic capacity at about Day 12 of pregnancy coincides with the rise in serum placental lactogen.

Prolactin and the regulation of adipose-tissue metabolism during lactation in rats

Removal of litters from young lactating rats for 24 or 48 h or treatment of lactating rats with bromocriptine increased the rate of fatty acid synthesis and the activities of lipoprotein lipase and fatty acid synthetase in adipose tissue, decreased the lipoprotein lipase and fatty acid synthetase activities of mammary gland and lowered the serum-prolactin concentration. Concurrent injections of prolactin prevented the effects of bromocriptine and 24 h of litter removal on most of these changes in adipose tissue, but did not prevent the effects of 48 h of litter removal. The results suggest that effects of prolactin on adipose-tissue metabolism are dependent on a functional mammary gland. Most of the responses of adipose tissue to litter removal were reduced in older rats.