A decreased n-6/n-3 ratio in the fat-1 mouse is associated with improved glucose tolerance

A reduction in skeletal muscle fatty acid oxidation (FAO), manifested as a reduction in mitochondrial content and (or) FAO within mitochondria, may contribute to the development of insulin resistance. n-3 polyunsaturated fatty acids (PUFA) have been observed to increase the capacity for FAO and improve insulin sensitivity. We used the fat-1 mouse model, a transgenic animal capable of synthesizing n-3 PUFA from n-6 PUFA, to examine this relationship. Fat-1 mice exhibited a approximately 20-fold decrease in the n-6/n-3 ratio in skeletal muscle, and plasma glucose and the area under the glucose curve were significantly (p < 0.05) lower in fat-1 mice during a glucose challenge test. The improvement in whole-body glucose tolerance in the fat-1 mouse was associated with a approximately 21% (p < 0.05) decrease in whole-muscle citrate synthase (CS) activity (in red muscle only), without alterations in CS activity of isolated mitochondria (either red or white muscle; p > 0.05). These data suggest that the fat-1 mouse has decreased skeletal muscle mitochondrial content. However, the intrinsic ability of mitochondria to oxidize fatty acids was not altered in the fat-1 mouse, as rates of palmitate oxidation in isolated mitochondria from both red and white muscle were unchanged. Overall, this study demonstrates that a decrease in the n-6/n-3 ratio can enhance glucose tolerance in healthy animals, independent of changes in mitochondrial content.

Flaxseed does not antagonize the effect of ultra-low-dose estrogen therapy on bone mineral density and biomechanical bone strength in ovariectomized rats

A previous study showed that flaxseed (FS) combined with low-dose (LD) estrogen therapy, resembling LD transdermal estrogen therapy in postmenopaual women, inhibited loss of bone mineral density (BMD), bone mineral content (BMC), and strength in lumbar vertebrae in ovariectomized rats. Whether FS combined with an even lower dose of estrogen is effective at preserving bone or whether FS interferes with the effect of this lower dose of estrogen is unknown. Thus, this study determined whether an ultra-low-dose (ULD) estrogen therapy, half the dose previously studied, in combination with FS preserved bone mass and strength in the lumbar vertebrae in ovariectomized rats. Rats were treated for 12 wk with (1) basal diet (BD) (ovariectomized control), (2) BD + ULD estrogen implant, or (3) BD containing 10% FS + ULD estrogen implant. A sham-operated control group was fed BD. Unlike ULD, FS + ULD attenuated loss of BMD and strength at the lumbar vertebrae and BMD in femurs and tibias. FS + ULD resulted in higher percentages of n-3 fatty acids including alpha-linolenic acid and eicosapentaenoic acid and lower percentages of n-6 fatty acids including linoleic acid compared to all other groups. Differences in fatty acid composition at the lumbar vertebrae and tibia were significantly related to BMD, BMC, and strength. No treatment-induced effects on uterus weight were observed, but histological analyses are needed to confirm safety. In conclusion, FS did not antagonize the activity of ULD, and their combination attenuated the loss of BMD and strength at the lumbar vertebrae, which was associated with differences in bone fatty acid composition.

High multivitamin intake by Wistar rats during pregnancy results in increased food intake and components of the metabolic syndrome in male offspring

The effect of high multivitamin intake during pregnancy on the metabolic phenotype of rat offspring was investigated. Pregnant Wistar rats (n=10 per group) were fed the AIN-93G diet with the recommended vitamin (RV) content or a 10-fold increase [high vitamin (HV) content]. In experiment 1, male and female offspring were followed for 12 wk after weaning; in experiment 2, only males were followed for 28 wk. Body weight (BW) was measured weekly. Every 4 wk, after an overnight fast, food intake over 1 h was measured 30 min after a gavage of glucose or water. An oral glucose tolerance test was performed every 3-5 wk. Postweaning fasting glucose, insulin, ghrelin, glucagon-like peptide-1, and systolic blood pressure were measured. No difference in BW at birth or litter size was observed. Food intake was greater in males born to HV dams (P<0.05), and at 28 wk after weaning, BW was 8% higher (P<0.05) and fat pad mass was 27% higher (P<0.05). Food intake reduction after the glucose preload was nearly twofold less in males born to HV dams at 12 wk after weaning (P<0.05). Fasting glucose, insulin, and ghrelin were 11%, 62%, and 41% higher in males from HV dams at 14 wk after weaning (P<0.05). Blood glucose response was 46% higher at 23 wk after weaning (P<0.01), and systolic blood pressure was 16% higher at 28 wk after weaning (P<0.05). In conclusion, high multivitamin intake during pregnancy programmed the male offspring for the development of the components of metabolic syndrome in adulthood, possibly by its effects on central mechanisms of food intake control.