Acute and chronic vitamin C deficiency in guinea-pigs: its effect on ceruloplasmin and cytochrome P 450 and b5 levels

Serum and liver ceruloplasmin levels rose markedly in guinea pigs with acute scurvy and with chronic latent scurvy. Their increase in the former condition can be attributed to the general stress reaction, but the increase in ceruloplasmin levels in concentration may have a stimulant effect on the ceruloplasmin, when the oxidation of Fe2+ to Fe3+ is potentiated, may obstruct the binding of iron to protoporphyrin and prevent formation of the haeme of cytochrome P 450 and b5.     

Effect of medium-chain triglycerides and long-chain triglycerides on plasma pancreatic polypeptide secretion in man

Since it has been shown that stimulation of pancreatic enzyme secretion by triglycerides is dependent on the chain length of the fatty acids, we have studied whether the secretion of pancreatic polypeptide (PP) in response to triglycerides is also related to the chain length of the fatty acids. Therefore, the effect of equimolar amounts (60 mmol) of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT) on plasma PP was studied in 6 normal subjects. In the control study the subjects ingested 60 ml of 0.15 mol/l saline. Ingestion of LCT resulted in significant increases in plasma PP from 33 +/- 7 to 55 +/- 7 pmol/l (P less than 0.01), whereas both MCT and saline did not significantly increase plasma PP concentrations. Similarly, the integrated plasma PP secretion after LCT (1022 +/- 392 pmol/l per 90 min) was significantly greater than that after MCT (-690 +/- 358 pmol/l per 90 min; P less than 0.001) and that after saline (-462 +/- 205 pmol/l per 90 min; P less than 0.01). It is concluded that the secretion of PP in response to triglycerides is dependent on the chain length of the fatty acids.     

An assay for uracil in human DNA at baseline: effect of marginal vitamin B6 deficiency

Improvements are made to our gas-chromatography-mass-spectrometry-based assay for quantifying low levels of DNA-uracil. Folate deficiency leads to increased deoxyuridine monophosphate/thymidylate (dUMP/dTMP) ratios and uracil misincorporation into DNA, which may increase cancer risk. Vitamin B6 (B6) deficiency might also result in increased DNA-uracil because B6 is a cofactor for serine hydroxymethyltransferase, which catalyzes the methylation of tetrahydrofolate (THF) to methylene-THF, the folate form that is required to convert dUMP to dTMP. However, the low baseline levels of DNA-uracil in healthy human lymphocytes are difficult to measure accurately. This version of the assay (Uracil assay V3) has an approximately 10-fold increase in signal strength over the previous method and a 10-fold lower detection limit (0.2 pg uracil). Five micrograms of DNA, the amount in about 1 ml of human blood, is a suitable amount for this assay. Using this improved assay, DNA-uracil was measured in lymphocytes from 12 healthy smoking or nonsmoking young men and women who consumed a B6-restricted diet (0.7 mg B6/day, or approximately half the recommended dietary allowance) for 28 days. DNA-uracil concentration was not significantly related to B6 status or smoking. More severe and/or prolonged B6 deficiency may be necessary to detect significant changes in DNA-uracil in humans. The average concentration of DNA-uracil in these subjects was found to be approximately 3,000 uracils per diploid lymphocyte, which is comparable to steady state levels of one of the oxidative adducts of DNA, 8-oxoguanine.     

Abnormal regulation of IFN-gamma secretion in vitamin A deficiency

T lymphocytes from vitamin A-deficient (A-) mice show a decreased ability to stimulate B lymphocytes for Ag-specific secondary IgG1 responses in vivo and in vitro. Experiments reported here traced the molecular basis for this functional defect to an overproduction of IFN-gamma by A- CD4+ T cells compared with cells from A-sufficient (A+) mice. Secretion of IL-2 and IL-4 by cells from A- and A+ mice was equivalent. Retinoic acid supplementation in vitro decreased IFN-gamma secretion from A- T cells, indicating that IFN-gamma production is retinoid-responsive. Adding IFN-gamma neutralizing antibodies to cultures established with cells from immune A- mice substantially increased IgG1 production, whereas IL-4 addition moderately increased IgG1 production. Adding retinoic acid to the cultures either at initiation, or 48 h later, fully restored IgG1 production by A- cultures to the level of A+ control cultures. These results are consistent with a role for vitamin A in negatively regulating IFN-gamma secretion.     

The effect of magnesium deficiency on glucose stimulated insulin secretion in rats

Weanling Sherman rats were pair-fed for 8 days on a control or a magnesium deficient diet containing 70.5% sucrose. After a 12-hour fast, the rats were injected intraperitoneally with glucose (250 mg/100 g body weight) and arterial blood was drawn at 0, 15, 30, 60, 90 minutes after injection. Before glucose loading, in magnesium deficient rats, plasma magnesium levels were significantly increased. The plasma triglyceride concentration was significantly higher in magnesium deficient rats compared to controls. After glucose loading, in the control group, the plasma insulin concentrations increased to 67.9 +/- 5.8 microU/ml at 15 minutes and returned to pretreatment levels by 30 minutes; in the magnesium-deficient rats, the plasma insulin levels were significantly lower at 15 minutes 32.9 +/- 5.6 microU/ml (P less than 0.01) and returned more slowly to the pre-challenge level. No significant differences were observed in plasma glucose levels between the two groups of rats.