Effect of carbohydrate source on lipid metabolism in lactating mice and on pup development.

The effect of long-term sucrose intake on lipid metabolism and milk composition was examined in lactating mice and correlated with the development of their pups. Female mice were weaned onto semi-purified diets containing 685 g starch or sucrose/kg diet. Food intake was similar on the two diets. At mid-lactation, milk was collected and analysed. Milk from sucrose-fed dams had a lower percentage of linoleic acid (18:2n-6) and a higher percentage of oleic acid (18:1n-9), although milk fat content was similar. Hepatic fatty acid synthesis (as measured by 3H2O incorporation into fatty acid) was three times faster in sucrose-fed than in starch-fed dams. Dietary carbohydrate had no effect on fatty acid synthesis or functional lipoprotein lipase (EC 3.1.1.34) activity in mammary gland, nor on plasma triacylglycerol concentration. Pups from first litters were killed at 11-12 d and body composition analysed. Pups born to sucrose-fed dams were significantly heavier with increased body fat and higher levels of plasma glucose and triacylglycerol. Litters of sucrose- and starch-fed dams were cross-fostered at birth and killed at 10-12 d. Analysis of variance indicated that maternal sucrose intake, both during pregnancy and lactation, increased body fat of offspring. The increases in body weight and plasma triacylglycerol of preweaning offspring were caused primarily by maternal sucrose intake during lactation.

Fatty acid and cholesterol synthesis in mice infected with the tapeworm Hymenolepis microstoma.

Infection with Hymenolepis microstoma significantly affected the lipid metabolism of young male Balb/C mice. Infection increased the rates of hepatic fatty acid and cholesterol synthesis and cholesterol synthesis by the gut. Decreases were recorded in testicular fatty acid synthesis and in the weights of testes and white epididymal adipose tissue. Plasma glucose decreased rapidly during infection. The observed changes in lipogenesis could not be attributed to changes in food intake or body temperature. The changes are discussed in relation to nutritional interactions between host and parasite and the possible effects on host hormone levels. The presence of newly synthesized fatty acid in H. microstoma is also reported.

Regulation of fatty acid synthesis and malonyl-CoA content in mouse brown adipose tissue in response to cold-exposure, starvation or re-feeding.

1. The effect of nutritional status on fatty acid synthesis in brown adipose tissue was compared with the effect of cold-exposure. Fatty acid synthesis was measured in vivo by 3H2O incorporation into tissue lipids. The activities of acetyl-CoA carboxylase and fatty acid synthetase and the tissue concentrations of malonyl-CoA and citrate were assayed. 2. In brown adipose tissue of control mice, the tissue content of malonyl-CoA was 13 nmol/g wet wt., higher than values reported in other tissues. From the total tissue water content, the minimum possible concentration was estimated to be 30 microM 3. There were parallel changes in fatty acid synthesis, malonyl-CoA content and acetyl-CoA carboxylase activity in response to starvation and re-feeding. 4. There was no correlation between measured rates of fatty acid synthesis and malonyl-CoA content and acetyl-CoA carboxylase activity in acute cold-exposure. The results suggest there is simultaneous fatty acid synthesis and oxidation in brown adipose tissue of cold-exposed mice. This is probably effected not by decreases in the malonyl-CoA content, but by increases in the concentration of free long-chain fatty acyl-CoA or enhanced peroxisomal oxidation, allowing shorter-chain fatty acids to enter the mitochondria independent of carnitine acyltransferase (overt form) activity.

Effect of substrate interactions on in vitro fatty acid synthesis in adipose tissue of normal and genetically obese mice.

Fatty acid synthesis was measured in vitro in pieces of adipose tissue from lean and obese-hyperglycaemic (ob/ob) mice, using 14C-glucose or 14C-lactate and 3H2O to obtain absolute rates of total fatty acid synthesis. In the presence of lipoprotein-triglyceride (2.5 mumol/l) metabolic interaction occurred which decreased glucose incorporation into fatty acids by 30% in lean mouse tissue, but not in obese mouse tissue. In the absence of added insulin, the contribution of glucose to total fatty acid synthesis was 69% in obese mouse tissue, significantly lower than the value of 87% obtained in lean mouse tissue. Insulin increased the contribution of glucose to total synthesis in both lean and obese mouse tissues, although the value in obese mouse tissue (83%) remained lower than the value in lean mouse tissue (100%). Lactate was not a major precursor for fatty acid synthesis. When both lactate (2 mmol/l) and glucose (15 mmol/l) were present, the contribution of lactate to total fatty acid synthesis was not increased in obese mouse tissue, suggesting that even in the presence of insulin, about 30% of the carbon was provided by intracellular precursors.

Influence of age and genetic background on in vivo fatty acid synthesis in obese (ob/ob) mice.

The relationship of developing obesity and hyperinsulinaemia to fatty acid synthesis in whole body and major tissues has been studied in two strains of genetically obese (ob/ob) mice using in vivo incorporation of 3H2O into fatty acids. Rates of fatty acid synthesis were not increased in pre-weaning C57BL/6J obese mice even though hyperinsulinaemia and obesity occurred. Post-weaning, rates of fatty acid synthesis increased to 5 weeks of age in adipose tissue, liver and carcass, the latter being the major site of synthesis. Synthesis then declined in carcass and adipose tissue, but remained unchanged in liver at 3 months. Increased fatty acid synthesis developed earlier in Imperial College obese mice as compared to the C57BL/6J strain and total rates of synthesis were 3--5 times greater. Adipose tissue was the major site of synthesis in Imperial College obese mice, while carcass was of only minor importance. Thus genetic background and age strongly affected rates of fatty acid synthesis and also the extent to which various tissues contributed.

Use of tritiated water for measurement of 24-hour milk intake in suckling lean and genetically obese (ob/ob) mice.

A non-invasive method has been developed for measuring milk intake of suckling mice under physiological conditions. This method was used to determine whether genetically obese (ob/ob) mice are hyperphagic at 10 and 15 days of age. Lactating dams were injected with tritiated water (3H2O), which equilibrated in body water within 30 minutes. A constant specific activity of 3H2O was maintained over a 24-hour period by provision of 3H2O in drinking water. Tritium accumulation in body water of pups was proportional to their milk intake. After 24 hours, pups were removed from the dam, weighed, and blood samples (less than 10 microliters) obtained for assay of plasma 3H content by liquid scintillation counting. Body water content was computed from body weight. The composition of mouse milk taken from dams on days 10 and 15 of lactation was analyzed both volumetrically and gravimetrically. Water content was 68 to 69%; lipid content was 20% on day 10, 17% on day 15. At 10 days, mean milk intake was 0.96 ml, independent of litter size. At 15 days, intake per pup tended to decrease, from 1.4 to 0.8 ml, with increasing litter size. Using this method we have established that under physiological conditions ob/ob mice, which were identified as such at 4 to 5 weeks of age, do not have increased milk consumption at either 10 or 15 days of age.

Fatty acid synthesis in liver and adipose tissue of normal and genetically obese (ob/ob) mice during the 24-hour cycle.

1. The synthesis of long-chain fatty acids de novo was measured in the liver and in regions of adipose tissue in intact normal and genetically obses mice throughout the daily 24h cycle. 2. The total rate of synthesis, as measured by the rate of incorporation of 3H from 3H2O into fatty acid, was highest during the dark period, in liver and adipose tissue of lean or obese mice. 3. The rate of incorporation of 14C from [U-14C]glucose into fatty acid was also followed (in the same mice). The 14C/3H ratios were higher by a factor of 5-20 in parametrial and scapular fat than that in liver. This difference was less marked during the dark period (of maximum fatty acid synthesis). 4. In normal mice, the total rate of fatty acid synthesis in the liver was about twofold greater than that in all adipose tissue regions combined. 5. In obese mice, the rate of fatty acid synthesis was more rapid than in lean mice, in both liver and adipose tissue. Most of the extra lipogenesis occurred in adipose tissue. The extra hepatic fatty acids synthesized in obese mice were located in triglyceride rather than phospholipid. 6. In adipose tissue of normal mice, the rate of fatty acid synthesis was most rapid in the intra-abdominal areas and in brown fat. In obese mice, all regions exhibited rapid rates of fatty acid synthesis. 7. These results shed light on the relative significance of liver and adipose tissue (i.e. the adipose 'organ') in fatty acid synthesis in mice, on the mino importance of glucose in hepatic lipogenesis, and on the alterations in the rate of fatty acid synthesis in genetically obese mice.