Integration of metabolism in tissues of the lactating rat

Energy Allocation in Mammalian Reproduction

“…Thus, data from studies not controlling for lactation stage are difficult to evaluate. Second, because significant increases occur during lactation in various behaviors {e.g., activity cycle, nest building, huddling, aggression, licking: see Ewer, 1973;Leuthold, 1977;Galef, 1981;Glutton-Brock et al, 1982;Ostermeyer, 1983;Gittleman, 1988è) and in anatomical weight {e.g., mammary tissue, gut, heart: see Williamson, 1980;Sampson and Jansen, 1984), it is difficuh to tease apart the relative energetic costs of lactation (milk production) versus these other factors. Future studies should include measurements of energy use in various aspects of lactation, not only those associated with milk production.…”

Control of fatty acid synthesis in lactation

“…There is a net uptake of lactate by rat (Williamson, 1980) and goat (Linzell, 1974) mammary gland indicating that lactate may contribute to fatty acid synthesis in vivo. Glucose oxidation by the pentose phosphate pathway is thought to be the major source of NADPH for fatty acid synthesis in rat mammary gland, the remainder being derived from malate oxidation by malate dehydrogenase (NADP+) (Bauman & Davis, 1974.…”

“…Contributions of most other sites to total fatty acid synthesis, including brown adipose tissue, are small but some, such as the back, head and skin, make an appreciable contribution (Hollands & Cawthome, 1981). Agius & Williamson (1980~) showed that in the rat, although the rate of fatty acid synthesidg brown adipose tissue was relatively high, the total mass of brown adipose tissue was so small that the contribution to Williamson, 1981). A fall in total activity of acetyl-CoA carboxylase in the mammary gland and also the proportion in the active state occur on fasting in the rat (McNeillie & Zammit, 1982); there is also a decrease in the active proportion of pyruvate dehydrogenase in the active state but no change in total activity (Kankel & Reinauer, 1976;Baxter & Coore, 1978) which is at least partly due to a fall in pyruvate dehydrogenase phosphatase activity (Baxter & Coore, 1979).…”

“…A fall in total activity of acetyl-CoA carboxylase in the mammary gland and also the proportion in the active state occur on fasting in the rat (McNeillie & Zammit, 1982); there is also a decrease in the active proportion of pyruvate dehydrogenase in the active state but no change in total activity (Kankel & Reinauer, 1976;Baxter & Coore, 1978) which is at least partly due to a fall in pyruvate dehydrogenase phosphatase activity (Baxter & Coore, 1979). Other factors appear to be involved, since the fall in the rate of fatty acid synthesis is much greater than the fall in acetyl-CoA carboxylase (active state) (McNeillie & Zammit, 1982) and, when lactating rats were fasted and then refed for 2 h, there was almost complete restoration of the rate of fatty acid synthesis (Williamson, 1980) but no change in the proportion of pyruvate dehydrogenase (Kankel & Reinauer, 1976) Regulation How are these changes in the rate of fatty acid synthesis in the various organs produced? Lactation is exceptional in that reciprocal changes occur in different tissues whereas other conditions such as fasting, diabetes and feeding high-fat diets, decrease the rate of fatty acid synthesis at all sites (Williamson, 1980).…”

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A 6 gHL,

Scot LandLactation results not only in major changes in the metabolism of the mammary gland, but also in the metabolism of other organs of the body, for it is clear that the massive demands which lactation imposes on the body require a co-ordinated adaptation of metabolism in the whole animal (Bauman & Currie, 1980;Williamson, 1980). Fatty acid synthesis provides a good example of such co-ordinated adaptation, for changes in lipogenic activity during lactation have been shown to occur in liver, white adipose tissue and brown adipose tissue as well as in the mammary gland.

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