| Popis: |
The effects of alterations in endocrine and nutritional state on lipogenesis in vivo in mammary gland, liver, white and brown adipose tissue (WAT,BAT) of the lactating rat were investigated. During lactation, lipogenesis was increased in liver, decreased in BAT and unchanged or decreased in WAT; the mammary gland was the major site of lipogenesis. Insulin administration did not increase lipogenesis in the gland any further but it increased it in liver, WAT and BAT. Removal of the pups or suppression of prolactin secretion increased the plasma insulin concentration and lipogenesis in liver, WAT and BAT. There may be a reciprocal relationship between plasma prolactin and insulin, and the hypoinsulinaemia of lactation may be important in restricting lipogenesis in liver, WAT and BAT to promote the direction of glucose to the gland. An oral load of glucose increased lipogenesis in vivo 2-fold in liver of virgin and lactating rats and 8-10- fold in BAT of virgin rats but had no effect on BAT of lactating rats. BAT slices from lactating rats showed decreased rates of lipogenesis in vitro. An oral load of medium- or long-chain triacylglycerol inhibited lipogenesis in mammary gland in vivo (82-89%) This inhibition was reversed when the acini were incubated in vitro. Insulin administration reversed partially the inhibition of lipogenesis in vivo. Long-chain triacylglycerol inhibited hepatic lipogenesis in vivo but medium-chain triacylglycerol increased it 2-fold. Lactating rats fed a high-energy diet had a decreased rate of mammary gland lipogenesis in vivo (60-80%). Glucose uptake and lipogenesis by the isolated acini in vitro correlated with the depressed lipogenesis in vivo. Insulin in vitro reversed glucose uptake and lipogenesis to values approaching those of controls fed on chow diet. In lactating rats the high-energy diet did not affect hepatic and WAT lipogenesis but it increased BAT lipogenesis. In virgin rats the high-energy diet increased WAT lipogenesis but it decreased hepatic and BAT lipogenesis. It is concluded that in lactating rats the highenergy diet results in a decrease in sensitivity of the mammary gland to insulin and in increased partitioning of carbohydrate to BAT while in virgin rats excess carbohydrate is partitioned to lipogenesis in WAT. |
