1. Method of recording the heart rate in rats is described.
2. It was found that during the course of developing thiamin deficiency, the heart rate of rats dropped from 448 to 220 beats/min. (There was no difference between male and female rats.)
3. A number of metabolic products were injected into the normal rats and only glyoxylate was shown to cause a significant drop in heart rate.
4. Graded amounts of Na-glyoxylate were injected peritoneally into the normal rats and blood samples were taken at intervals to test the amount of glyoxylate present. It was found that peak concentra-tion appeared 6min after injection and thereafter declined or disappeared, depending on the amount of glyoxylate administered.
5. It was found that glyoxylate accumulates in the body of thiamin-deficient rats and in the pair-fed rats reared on restricted diet for a long period.
6. Drop in heart rate depended on the appearance of glyoxylic acid present in the blood rather than on the reduction of body weight.

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Escherichia coli KG980, a vitamin B₆ auxotroph derived from E, coli K12, utilized the three unphosphorylated forms of vitamin B₆, more or less effectively, for growth, but did not utilize the three phosphate forms at concentrations ranging from 10^-7 to 10^-5 M in the minimum medium of Davis and Mingioli. The bacterium, however, utilized the phosphate forms, although less effectively than the un-phosphorylated forms, in the phosphate starving medium of Garen and Levinthal which is known to derepress alkaline phosphatase. Cor-respondingly, the phosphate forms of ³H-labeled vitamin B₆ in the minimum medium were not taken up by the bacterial cells grown in the same medium, but were taken up when the phosphate starving medium was used for growth and uptake experiments; the unphosphorylated forms were taken up with either of the media used. After 30-min in-cubation of the cells grown in the phosphate starving medium with ³H-pyridoxine phosphate added to the same medium, the main extra-cellular ³H-vitamin B₆ was found to be pyridoxine, evidently indicating an involvement of alkaline phosphatase action. It is concluded from these results that the phosphate forms of vitamin B₆ can be taken up and utilized only after dephosphorylation but not taken up in their intact form. The initial rate of ³H-pyridoxal and ³H-pyridoxamine uptake in the minimum medium showed saturation kinetics. The K_m and V_max values were 1.2×10^-6 M and 62 pmoles/min/mg (dry cell weight) for pyridoxal; 11×10^-6 M and 65 pmoles/min/mg for pyridoxamine. ³H-Pyridoxine uptake apparently consisted of a high-affinity saturable component, whose K_m value was tentatively estimated to be 2.2×10^-6 M, and an unsaturable component. The uptake rates of these three un-phosphorylated vitamin B₆ compounds compared at limiting concentra-tions for the growth of E. coli KG980 appear to be essentially in good agreement with the response pattern of this bacterium to the three compounds.

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Investigations were carried out to obtain information on the effect of vitamin B₆ level on L-glutamate dehydrogenase activity in mice brain. Subcutaneous and intracerebral injection of pyridoxal phosphate or pyridoxamine resulted in a significant enhancement of the L-glutamate dehydrogenase activity. In the case of pyridoxine, much larger doses and more prolonged time were necessary to exhibit the effect. The above effect of vitamin B₆ was much more evidently observed in vitamin B₆-deficient animals.

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In the present paper, the nucleotide precursor of riboflavin was investigated by experiments with labeled purines using non-growing cells of Eremothecium ashbyii.
The added purines, at 10^-4 M, were effectively incorporated into ribo-flavin at an early stage of riboflavin biosynthesis under the experimental conditions. In particular, both labeled xanthine and labeled guanine were specifically transported to guanosine nucleotides, GMP, GDP, GDP-Mannose and GTP, in the cource of the riboflavin biosynthesis. A comparison of specific activities of labeled guanosine nucleotides and labeled riboflavin indicated that the nucleotide precursor of riboflavin is guanosine triphosphate. From the results obtained, a biosynthetic pathway of riboflavin is proposed under “DISCUSSION.”

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Three groups of male rats were maintained on diets con-taining different amounts of fat. After one week on such regimens, they were injected intraperitoneally with cholesterol-³H. During the following 28 days, the radioactivity and quantity of fecal cholesterol and its metabolites were determined. The coprostanol excretion was the about same in all groups and the bile acids excretion increased with increasing fat intake; however, compared to the fat-free group, the excretion of the injected cholesterol-³H was greater in the 3% fat group and less in the 10% fat group. Consequently, the specific radioactivity of bile acids was lower in the 10% group than in the others. The half-life of labelled cholesterol was 12.6, 16.0 and 22.2 days for the 3%, 10 fat and fat-free groups, respectively. Rather than a fat-free diet, a low-fat diet of 3% or so, would be of more advantage in eliminating choleste-rol by increasing the formation of bile acids to emulsify the fat. In the 10% fat group, however, the enlarged pool size of bile acid probably delayed cholesterol metabolism to bile acids.

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This study was conducted to investigate the long-term effect of dietary medium-chain triglyceride (MCT) as compared with that of corn oil feeding on lipid metabolism in rats. Both serum choles-terol and triglyceride levels in MCT-fed rats showed significant decrease during the experimental period of eight weeks, although liver cholesterol and triglyceride contents were not distinguishable between the two groups. Significant elevation of the activity of lipogenic enzymes, such as fatty acid synthetase (FAS) and malic enzyme (ME) of the liver, was ob-served in MCT-fed rats without any fat accumulation of the liver (fatty liver). The increase of lipogenic enzyme activity was accompanied by a significant reduction of essential fatty acids (EFA) such as 18:2 (ω6) and 20:4 (ω6) in total liver lipid. In contrast, hepatic β-hydroxy-β-methylglutaryl CoA (HMG-CoA) reductase activity was significantly de-creased in MCT-fed rats, that would play an important role in achieving hypocholesterolemia. From these results obtained in a long-term ex-periment, it is concluded that exogenous MCT depresses the key en-zyme catalyzing cholesterol synthesis with a concomitant elevation of lipogenic enzyme activity in the rat liver.

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