Summary The effect of vitamin B12 (B12) deficiency on the levels of S-adenosylmethionine (SAM) in tissues and the activities of hepatic me-thionine synthase, methionine adenosyltransferase and glycine N-methyltransferase were investigated. The striking depression of me-thionine synthase activity was observed in all rats fed the B12-deficient diets with or without methionine supplementation for 150 days. The SAM level in liver was decreased by B12 deficiency. However, brain SAM level was not affected. The activities of hepatic methionine adenosyltrans-ferase isozymes, α-form and β-form, were decreased by B12 deficiency. Hepatic glycine N-methyltransferase activity in rats fed the low methionine-B12-deficient diet showed a tendency to lower, although the change the activity was not statistically significant, compared with B12-supplemented rats. It is proposed that the fall in the activity of hepatic methionine adenosyltransferase may be one of the causes of the decreased hepatic SAM level in B12-deficient rats.
When 400 mg/rat/day of secondary autoxidation products of linoleic acid was orally administered 3 times to rats, they died at 30-40 h after the third dose. To search the markers of the toxicity of secondary products in vivo, the rats were killed at 24 h after the third dose, and conditions of their digestive tracts and liver were analyzed. In the stomach, macroscopically, inflation, retention of undigested food, and edema were seen. Slight congestions were detected in the small intestines. It was considered that these injuries led to reduction in food consumption and then depression of the growth, but did not lead to the death of the animals. The lipid peroxide levels in the liver and the activities of its detoxifying enzymes were increased as compared to those in the control groups. The hepatic lipid contents and unsaturated fatty acid compositions were also not changed. The endogenous lipid peroxidation, therefore, did not give the rats a severe stress. The activities of hepatic acetyl-CoA carboxylase and carnitine palmitoyltransferase were 20 and 35% lower than those of control, respectively. The levels of CoASH, acetyl-CoA, and long-chain acyl-CoA were 1/9, 1/2, and 1/4 of those in control, respectively. Thus, one of the markers of the toxicity of secondary products was the depletion of hepatic CoA derivatives. In rat, bio-energy was reduced by the decrease in the intestinal absorption of nutrients, and the depletion of hepatic CoA derivatives also failed to supply energy with β-oxidation.
In order to find the markers of the toxicity of the autoxi-dized lipids in the liver, rats were given a lethal amount of secondary autoxidation products of linoleic acid (400mg/rat/day for 3 days) and then changes in the hepatic metabolic functions were analyzed. A decrease in acetyl-CoA level to half caused by the depletion of CoASH was reported in an associated paper (J. Nutr. Sci. Vitaminol, 35, 11-23, 1989). Citrate, isocitrate, and 2-oxoglutarate also decreased to half the level of those of the control group. Reduction in isocitrate dehydrogenase activity was only 25%, while NADH2 and ATP levels remained unchanged. Thus, the reduction in the citrate cycle activity was due to the decrease in acetyl-CoA. The activity of mitochondrial succinate dehydrogenase was de-creased to 1/5. Other appreciable changes were depletion of glucose 6-phosphate and fructose 6-phosphate, accumulation of glucose 1-phos-phate, reductions in hexokinase, phosphofructokinase, glucose-6-phos-phatase, phosphoglucomutase, and phosphogluconate dehydrogenase activities, and decrease in the NADPH2 level. It was considered that these changes were caused by the depletion of glucose 6-phosphate whose synthetic pathways were abnormal. Therefore, the markers of the hepatotoxicity of secondary products were the changes in the CoASH level and the activities of succinate dehydrogenase and synthetic pathways for glucose 6-phosphate.
The influence of cooking and later storage in a refrigerator for 7 days on the fatty acid composition of lipids in sardines (Sardinops melanosticta) was studied. The total lipid and triacylglycerol (TG) levels did not change and the phospholipid (PL) level decreased somewhat with cooking or during storage. The fatty acid composition of the total lipids and TG fractions was little changed and that in the PL fractions was somewhat changed by the cooking. The composition of the poly-unsaturated fatty acids (PUFA) in lipids of sardine precooked at 100 or 170°C for 30 min changed from 42.7 to 38.3 or 33.5%, respectively, for total lipids and from 51.5 to 38.4 or 37.6%, respectively, for PL fractions during storage. The fatty acids in lipids from the ordinary meat of sardine was stable and those in the dark meat were extremely unstable during storage after cooking. We concluded that the PUFA in the lipids of sardines were stable to cooking, but unstable to oxidation during storage in a refrigerator. The PUFA of lipids in the dark meat of sardine were extremely unstable to oxidation.
Phagocytosis of opsonized sheep red blood cells (SRBC) by alveolar macrophages (AM) was measured in rats fasted for 1 to 9 days or fed on diets restricted 20 to 95% compared to control group for 2 and 8 weeks. In rats fasted for 1 to 6 days, AM showed an increased phago-cytosis at 2 days after fasting, but their phagocytic activity remarkably decreased afterwards. Furthermore, phagocytic activity of AM per rat revealed much more decrease at 3 to 6 days after fasting. Then the production of interleukin-1 (IL-1) by AM increased with prolonged fasting, but the production of prostaglandin E2 (PGE2) by AM cultured with lipopolysaccharide (LPS) conversely decreased in rats fasted for 2 days or longer. The proliferation of splenocytes increased with prolonged fasting. On the other hand, 20 to 95% restricted diets induced the increased phagocytosis of AM with prolonged experimental period. However, phagocytic activity of AM per rat showed significant increase only in rats on a 40% restricted diet. The findings suggest that differences in both duration and degree of dietary restriction modulate phagocytic function of AM, and may contribute to explaining, in part, conflicting observations which have been obtained on the immunologic state in malnourished animals.
The formation of L-ascorbic acid (AsA) was observed when dehydro-L-ascorbic acid (DHA) was dissolved in neutral buffer solutions under N2 bubbling at room temperature. The reduction of DHA was done with the lactonized compound of 2, 3-diketo-L-gulonic acid (DKG), that is, the 3, 4-endiol form of 2, 3-diketo-gulono-b-lactone (3, 4-End DKGL). 3, 4-End DKGL was formed from DHA or DKG (yield about 10%) under N2 bubbling in neutral buffer solution (pH 7.2). This material was not stable in neutral or alkaline solutions. 3, 4-End DKGL suppressed more strongly the linoleic acid (LA) peroxidation in the medium containing 20% EtOH and 10mM LA than did AsA. This may suggest the possibility that 3, 4-End DKGL reproduces AsA from DHA in physiological status.
An a-amylase inhibitor was prepared from cranberry bean (Phaseolus vulgaris). The α-amylase inhibitor was composed of three different subunits not linked by disulfide bridges and only one of them contained carbohydrate. Although the inhibitor was stable at pH 3 to 7, it was heat labile at pH 3 and 5. Chemical modification of the amino groups and the guanido groups in cranberry bean a-amylase inhibitor molecule resulted in rapid loss of the inhibitory activity, respectively. Oxidation of the tryptophan residues also led to loss of the activity. On the other hand, reductive methylation of the amino groups scarcely affected the activity. The inhibitor was quite resistant to the proteolytic digestions by pepsin and trypsin, while it was relatively susceptible to the action of chymotrypsin.
The nutritive utilization of magnesium and calcium was studied using two different formulations of Mg: MgCO3 and an organic dietary Mg preparation. The influence of supplementation with the latter was also studied. The dietary organic magnesium did not modify food intake, which remained adequate in all animals used in the present experiments. Magnesium in both inorganic compound and organic pre-paration form was well absorbed; furthermore, absorption levels of the latter remained quite stable throughout the different experimental periods. Mg balance in both muscle and femur was similar in all groups studied. Digestive utilization of Ca and Ca content in the longissimus dorsi were higher in animals fed the organic Mg preparation while Ca levels in blood and femur were not affected.
The blood pressure of spontaneously hypertensive rats (SHR) were significantly reduced by Maitake feeding for 8 weeks period beginning at a time when the animals were 10 weeks of age with well-established high blood pressure. There was no difference in the plasma total and free cholesterol, triglyceride and phospholipid levels between the Maitake fed animals and the control, On the other hand, Shiitake mushroom did not reduce the blood pressure, but significantly lower the plasma free cholesterol, triglyceride and phospholipid in compared with the control. The results suggest that dietary Maitake mushroom reduce the blood pressure.