Relationship between growth and selected liver enzyme activities of individual rainbow trout

Interpretation of enzymatic data requires consideration of the food intake of each animal studied. Food intake and body mass gain are closely correlated in rapidly growing animals. Direct measurement of food intake by individual fish within a school is nearly impossible. We examined the relationship between growth and liver enzyme activity as a means of inferring the food intake of individual fish within a school. Trout, identified by passive integrated transponder implants, were fed either 0, 0.3, 1, or 2% body mass/d to produce a wide range of growth rates. The activities of five enzymes, predominantly localized in liver, were measured. Results showed that, although the magnitude of response differed, increases in total liver activities of all five enzymes measured were linearly related to growth. Hexokinase (EC 2.7.1.1) increased at a rate below, and beta-D-glucose:NAD(P)+1-oxidoreductase (EC 1.1.1.47) increased at a rate equivalent to, observed increases in total liver mass. Malic enzyme (EC 1.1.1.40), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44) showed preferential increases in activity as food intake increased. Correlation of enzyme activities measured in fish fed restricted rations with either growth or nominal feeding rate showed that growth of individual fish was more closely related to liver enzyme activities than nominal feeding rate.

Thiamin absorption is not compromised in folate-deficient rats

Thiamin absorption and excretion were assessed in rats with severe folate deficiency (FD) by determining the fate of oral 3H-labeled and intravenous 14C-labeled thiamin over a 6-h test period. Thiamin status was evaluated in these same rats by measuring transketolase activity levels of blood before (TKA) and after (TPPE) addition of thiamin pyrophosphate to the incubation mixture of the assay procedure. Two additional experiments assessed active transport of thiamin and the effect of dietary succinylsulfathiazole (SST) on TKA and TPPE in rats with moderate FD. Intestinal absorption in general and thiamin absorption in particular and thiamin status were unaltered in rats with severe FD. Inanition associated with severe FD may impair thiamin status. Thiamin absorption by active transport was not compromised in FD, and dietary succinylsulfathiazole did not affect thiamin status.

Folate deficiency in rats fed diets containing free amino acids or intact proteins

Development of folate deficiency (FD) was evaluated in weanling rats fed diets containing mixtures of free amino acids or of vitamin-free casein and gelatin as sources of dietary nitrogen. FD could be produced in 21 d with amino acid diets that promoted maximum growth rate, were completely devoid of folate and contained 1% succinylsulfathiazole. Growth retardation and blood dyscrasia associated with FD could not be demonstrated in rats fed diets containing casein and gelatin as nitrogen sources because the vitamin-free casein contained low but measurable levels of folate. The most effective protocol to produce experimental FD in rats is to feed a folate-free diet that otherwise supports maximum growth in young animals. Additional modifications such as use of methotrexate or amino acid-imbalanced or protein-deficient diets are unnecessary.

Purine synthesis and reutilization in folate-deficient rat hepatocytes

Although folic acid is known to be involved in the pathways of purine metabolism, the precise changes brought about in purine synthesis, reutilization, pool sizes, and ratios by experimental folate deficiency are not clear. Consequently, these aspects of purine metabolism were measured in hepatocytes from control and folate-deficient rats fed an amino acid diet with and without folic acid, respectively. Purine synthesis and reutilization were measured as the rates of incorporation of [U-14C]glycine and [G-3H]hypoxanthine, respectively, into the adenine and guanine pools of freshly isolated hepatocytes after a 3-hour incubation in folate-free, as well as folate- and/or thymidine-supplemented culture media. Hepatocytes from folate-deficient rats had the same rates of purine synthesis as those from control rats. Purine reutilization, purine pool sizes, and the adenine:guanine ratios were lower in hepatocytes from deficient compared with control rats. Purine synthesis was increased when folic acid or thymidine was added to the culture medium. Although hepatocytes from folate-deficient rats had a lower rate of purine reutilization compared with those from control rats, the reutilization rates did not respond to the addition of folic acid or thymidine to the culture medium. The data suggest that purine synthesis was not impaired but purine reutilization was diminished in folate deficiency. Thymidine was as effective as folic acid in stimulating purine synthesis in both control and folate-deficient hepatocytes.

Folate deficiency in rats fed amino acid diets

Growth rate, hematological changes, serum, erythrocyte and liver folate levels, and urinary excretion of formiminoglutamic acid (FIGLU) were measured in rats fed p-aminobenzoic acid (PABA)-free, sulfonamide-supplemented purified amino acid diets with and without folic acid and fiber, individually and in combination. Fiber had no effect on growth but was necessary to prevent mortality in the absence of folic acid. Folic acid did not affect growth during the first 40 days, but after this period rats failed to gain weight in the absence of folic acid. Although blood hematocrit was lower when the diet was devoid of fiber and folic acid and leucocyte counts were lower when the diets were devoid of folic acid, the hematological values remained within normal physiological limits for healthy rats of comparable age. FIGLU excretion was increased and serum, erythrocyte and liver folate levels were depressed when rats were fed folic acid-free diets for 28 days. Neutrophil hypersegmentation was clearly evident after 28 days of feeding the folic acid-free diets. The use of an amino acid diet without PABA but containing 5% fiber and 1% succinylsulfathiazole is a useful system to study chronic folic acid deficiency in the rat.