Regulation of lipogenic capacity in lactating rats

Abstract

1. The rate of mammary-gland lipogenesis measured in vivo from 3H2O was suppressed after decreasing the milk demand by decreasing the number of pups from ten to two or three, as well as by giving diets containing lipid [Grigor & Warren (1980) Biochem. J. 188, 61-65]. 2. The specific activities of the lipogenic enzymes fatty acid synthase, glucose 6-phosphate dehydrogenase and 'malic' enzyme increased between 6- and 10-fold in the mammary gland and between 2- and 3-fold in the livers during the first 10 days of lactation. The increases in specific activity coupled with the doubling of liver mass which occurred during pregnancy and lactation resulted in considerable differences in total liver activities when compared with virgin animals. 3. Although consumption of a diet containing 20% peanut oil suppressed the activities of the three lipogenic enzymes in the livers, only the 'malic' enzyme was affected in the mammary glands. 4. In contrast, decreased milk demand did not affect the specific activities of any of the liver enzymes, whereas it resulted in suppression of all three lipogenic enzymes of the mammary glands. There was no effect on either the cytoplasmic malate dehydrogenase or the lactate dehydrogenase of the mammary gland. 5. In all the experiments performed, the activity of the fatty acid synthase correlated with the amount of material precipitated by the rabbit antibody raised against rat fatty acid synthase.

Downregulation of peroxisome proliferator-activated receptor α and its coactivators in liver and skeletal muscle mediates the metabolic adaptations during lactation in mice

“…As carnitine is involved in b-oxidation by transferring fatty acids into the mitochondrion, inhibition of carnitine synthesis can be regarded also as a means to diminish fatty acid oxidation during lactation. On the other side, synthesis of fatty acids and TAG in the liver is enhanced during lactation, leading to an increased secretion of VLDL-TAG and an increased uptake of fatty acids from VLDL-TAG into the mammary gland due to the enhanced expression of Lpl (Farid et al 1978, Grigor et al 1982. Simultaneously, the uptake of NEFA derived mainly from lipolysis in white adipose tissue by fatty acid transporters into the mammary gland as well as de novo fatty acid synthesis catalyzed by lipogenic enzymes including Fas in the mammary gland is increased, which also enhances the pool of fatty acids in the mammary gland available for milk TAG production.…”

Biosynthesis of Fatty Acids by Lactating Human Breast Epithelial Cells: An Evaluation of the Contribution to the Overall Composition of Human Milk Fat

“…The tendency of the surfactant-deficient lung to collapse at end-expiration can be compensated for by a variety of therapeutic measures, such as the application of continuous positive airway pressure (3) or the adjustment of respiratory rate and inspiration/ expiration ratio during artificial ventilation (6). Recent data from animal experiments and clinical trials indicate that ventilation by HFO might represent yet another realistic alternative (for review, see Refs.…”

Transferrin-gene expression in the rat mammary gland. Independence of maternal iron status

“…1.5 mg/ml, falling to less than 0.5 mg/ml at days 5 and 10 of lactati.on and thereafter increasing for the remainder of lactation to reach values of greater than 4 mg/mi, or 4%0 of the total milk proteins, by day 20 of lactation. This pattern is quite unlike that for any other milk protein, and also differs from the pattern of expression of many mammary enzymes involved in lactose and lipid synthesis (Baldwin & Milligan, 1966;Kuhn & Lowenstein, 1969;Grigor et al, 1982). We have previously shown that the transferrin concentrations in rat milk can be manipulated by diet, being significantly lower in the milk of rats fed on either a low-protein diet or restricted amounts of a protein-adequate diet (Grigor et al, 1988).…”