Showing papers in "Journal of Nutrition in 1978"

Pathology of the Vitamin C Deficiency Syndrome in Channel Catfish (Ictalurus punctatus)

Abstract: Channel catfish fingerlings fed purified diets devoid of vitamin C showed reduced growth rate, deformed spinal columns, external and internal hemorrhages, erosion of fins, dark skin color and reduced bone collagen content after 8 to 12 weeks, whereas fish fed a diet containing 30 mg/kg of vitamin C had none of these anomalies after 22 weeks. A dietary level of 30 mg of vitamin C per kg was insufficient to prevent distortion of gill filament cartilage, although 60 mg of vitamin C per kg was sufficient. Vertebral collagen percentages of 25 or below and liver ascorbic acid levels of 30 microgram/g or below appeared to be indicative of vitamin C deficiency in channel catfish fingerlings. Epidermis and dermis were almost completely healed and extensive collagen fiber formation had commenced in the somatic muscle, in experimentally inflicted wounds after 10 days in fish fed the vitamin C-free diet. Skin and muscle at the wound site were almost regenerated to normal after 10 days in fish fed 60 mg of vitamin C per kg of diet.

Taurine: An Essential Nutrient for the Cat

Abstract: Cats fed a purified diet containing purified casein as the source of protein develop retinal degeneration due to the lack of taurine in the diet. To test whether cats can synthesize this sulfur amino acid from sulfate or cystine, radioisotopes of these substances were injected into taurine-depleted and control cats. Sulfate did not serve as a precursor for taurine synthesis, whereas cystine underwent only a moderate conversion to taurine. This is in keeping with the low level of cysteinesulfinic acid (CSA) decarboxylase activity in cat liver. There was no difference between the activity of CSA decarboxylase in tissues from control cats and that in tissues from taurine-depleted cats. The pattern of tissue accumulation of [35S]taurine and from [35S]cystine also indicated that tissues from taurine-depleted cats do not synthesize [35S]taurine more rapidly than tissues from control cats. The data did not indicate a difference in taurine uptake by tissues of control and deficient cats, but progressive accumulation in deficient cats suggested that the turnover rate of taurine is decreased by the deficiency. Since supplementation of the purified diet with cysteine has been found previously to be inadequate to prevent progressive taurine depletion of the retina and its subsequent degeneration and since conversion of sulfur compounds to taurine in vivo is inadequate, taurine can be considered an essential nutrient for the cat.

Hepatic cytosolic non selenium-dependent glutathione peroxidase activity: its nature and the effect of selenium deficiency

Abstract: Recent work had indicated the presence of a non selenium-dependent glutathione peroxidase activity in rat liver in addition to the selenium-dependent activity. The present study was undertaken to learn whether the glutathione S-transferases are reponsible for the non selenium-dependent glutathione peroxidase activity and to study the effect of selenium deficiency on those enzymes. Glutathione S-transferase B was purified by an established method using carboxymethyl cellulose ion exchange chromatography and studied. It exhibited glutathione peroxidase activity toward cumene hydroperoxide and t-butyl hydroperoxide. A limiting Km of 0.55 mM was determined for cumene hydroperoxide. Sulfobromophthalein was found to be a competitive inhibitor with respect to cumene hydroperoxide of the glutathione peroxidase activity of glutathione S-transferase B. Selenium deficiency caused an increase in glutathione S-transferase activity. These results establish that glutathione S-transferase B contributes to the non selenium-dependent glutathione peroxidase activity in rat liver and show that it increases in selenium deficiency when the selenium-dependent glutathione peroxidase is decreased.

Regulation by Dietary Fats of 3-Hydroxy-3-Methylglutaryl-Coenzyme a Reductase in Rat Liver

Abstract: TAKASHI IDE, HIROSHI OKAMATSU ANDMICHIHIRO SUGANOLaboratory of Nutrition Chemistry, Department of FoodScience and Technology, Kyushu University School ofAgriculture, Fukuoka 812 JapanABSTRACT The effects of various dietary fats on the activity of3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA ) reducA­asein rat livermicrosomes, the rate-limiting enzyme in cholesterogenesis, were examined.A series of experiments demonstrated the dependency of the HMG-CoAreducA­aseactivity on the nature of dietary fats. When saturated fats withchain length of 12 to 18 were the dietary sources and were fed at the 10%level for 19 days, feeding fats with shorter chain fatty acids caused a lowerenzyme activity compared to those with longer chain fatty acids. Theactivity was also regulated by the degree of unsaturation of dietary fats;when safflower oil, camellia oil or tristearin were fed at the 10% level for18 days, the higher the unsaturation, the lower the activity. When tri-myristin or tripalmitin were fed at the 10% level for 14 days, addition ofessential fatty acid, at the level of minimum daily requirement (1% wasreplaced by safflower oil), did not affect the enzyme activity. Though therate of incorporation of mevalonate into cholesterol in the 12,500 X gsupernatant fraction of the liver was also found to be influenced by thetypes of dietary fats, the extent of the response appeared much smallerthan that of HMG-CoA reductase. No consistent correlation between theHMG-CoA reductase activity and the content of microsomal cholesterol orcholesteryl ester and the fatty acid composition of microsomal lipids wasobserved. J. Nutr. 108: 601-612, 1978.INDEXING KEY WORDS hepatic cholesterogenesis •HMG-CoAreductase •dietary fats •essential fatty acid •microsomal cholesterol3-Hydroxy-3-methylglutaryl-Coenzyme A etary corn oil stimulated the enzyme ac-(HMG-CoA) reductase [EC 1.1.1.34] is tivity in proportion to the amount addedknown to be the rate-limiting enzyme of to a fat-free diet. In the hamster dietarycholesterogenesis in animal tissues. The ethyl palmitate stimulated, whereas ethylactivity of hepatic HMG-CoA reductase is linoleate, depressed, hepatic HMG-CoA re-controlled by the nutritional and hormonal ductase (6). Further information on thestate of the animals (1-3). One of the nu- effects of differences in the composition oftntional factors controlling the activity of dÂiet fats Qn th e actiyify of thethis enzyme in the liver is the amount and ,. , ., ,, u, . .A“nature of dietary fat. Craig et al. (4) ob- Ilver arf not available although there areserved in rats a decrease in the activity by some data showing that hepatic choles-changing the diets from a closed formula, terogenesis measured using acetate as anon-purified stock diet to a fat-free diet.

Intestinal Disappearance and Portal Blood Appearance of Amino Acids in Sheep

Abstract: The intestinal disappearance and simultaneous arterial inflow and portal appearance of individual amino acids (AA) were studied in sheep fed closed formula, unrefined high (H.P.) and medium (M.P.) protein diets. Gut contents were sampled through four intestinal cannulae and blood was sampled through portal and arterial catheters. The amount of total and amino N that was fed decreased on passage into the duodenum but increased in the jejunum, and then again decreased steadily towards the terminal ileum. The amounts of AA passing into the duodenum were significantly higher when the H.P. rather than the M.P. diet was fed. No dietary differences in AA were noted at the ileo-cecal junction, however, meaning that greater amounts of AA disappeared from the intestine when the H.P. diet was fed. The amounts of AA appearing in portal blood were 30 to 80% of those disappearing from the intestine and were greater in sheep fed the H.P. diet. The amount of AA passing into the duodenum also significantly affected the concentrations of AA in arterial blood. Less [U-14C]glutamic acid than [U-14C]alanine, that was infused into abomasum, was detected in the digesta passing through the pylorus. The same also was true for the unlabeled free form of glutamic acid. The portal appearance of both unlabeled and labeled glutamic acid was negligible, but that of alanine was considerable. Variable amounts of [14C]citrulline, [14C]arginine, and [14C]urea were detected in the blood following the abomasal infusions of labeled glutamic acid or alanine. The portal appearance of these labeled metabolites was always negative, however, implying that they were utilized, and not formed, by gut tissues.

The toxic level of sodium selenite in the diet of laying chickens.

Abstract: Female chickens were fed graded levels of sodium selenite to determine at what level a selenium toxicity occurred. In the first experi ment a basal diet was supplemented with 0, 0.1, 1.0, 3.0, and 5.0 ppm of selenium. These levels had no effect on egg production, egg weight or fertility of the eggs. Hatchability of fertile eggs was significantly decreased by 5 ppm of dietary selenium. In the second experiment a basal diet was supplemented with 0, 5.0, 7.0, and 9.0 ppm of selenium. Egg weight and hatchability were significantly decreased by 7 and 9 ppm, and egg produc tion was decreased by 9 ppm of selenium in the diet. When selenite was added to the diet, there was a lag of 2 to 3 weeks before the selenium con tent of the egg reflected the content of the diet. As long as the selenium content of the diet remained the same, egg selenium remained the same. When selenium was no longer supplemented, egg selenium content de creased. Two weeks after cessation of selenite supplementation, egg sele nium was markedly reduced. Four weeks after cessation of selenite supple- . mentation, egg selenium levels approached those of birds fed a basal diet continuously. J. Nutr. 108: 1114-1120, 1978.

Arginine: An Essential Amino Acid for the Cat

Abstract: The essentiality of arginine for the near-adult cat was demonstrated in three preliminary and two main experiments. In the pre liminary experiments, changing cats (body weights all in excess of 1.6 kg) from a purified diet containing a complete amino acid mixture (basal) to a similar isonitrogenous diet without arginine ( —Arg) caused rapid loss of body weight ( mean ±SE93.3 ±6.8 g in the first 24 hours ), emesis, and inappetance. In the main experiments the mean ±SE body weight of the cats was 2.6 ±0.4 kg. When eight of these cats were given the —Argdiet after an overnight fast, they all exhibited emesis, had tetanic spasms, and one died. Other symptoms included hypersalivation, depression which in some cases was followed by hyperesthesia, hyperactivity, ataxia, and dyspnea. The plasma of these cats showed hyperammonemia and hyperglycemia indicating that the clinical condition was caused by acute ammonia intoxi cation. The eight cats given the comparable diet with arginine showed no ill effects. Five cats given the basal diet with ornithine replacing arginine on an equimolar basis showed neither an increase in plasma ammonia nor glucose concentrations. Cats given the —Argdiet had extremely low 120 minute post-prandial levels of plasma free arginine (less than one-quarter of the prefceding level ). It was concluded that the cat lacks the ability to synthesize ornithine. The consequence of this metabolic deficiency in the cat is that arginine is an essential nutrient: it provides a unique example of a nutrient so critical that one meal without dietary arginine may result in death. The —Argdiet supported growth in young rats, albeit at a slower rate than rats fed the basal diet. J. Nutr. 108: 1944-1953, 1978. INDEXING

Effect of Pectin, Gum Arabic and Agar on Cholesterol Absorption, Synthesis, and Turnover in Rats

Abstract: A series of five experiments was conducted to determine the effect of pectin, gum arabic and agar (5%) on cholesterol absorption, biosynthesis and turnover in rats. In the study of cholesterol absorption, a tracer dose of labeled cholesterol was included in the last meal. The rats were killed 12 hours later. The proportion of the labeled cholesterol recovered in the whole body was used as an estimation of the efficiency of absorption of dietary cholesterol. Cholesterol biosynthesis was estimated by determining the activity of labeled digitonin-precipitable sterols biosynthesized from labeled glucose which was included in a test meal. In turnover studies, rats were injected intravenously with labeled cholesterol using serum as a vehicle, and the activity of labeled cholesterol in tissues was determined after various time intervals. All three complex carbohydrates decreased cholesterol absorption and pectin had the greatest effect. Pectin and gum arabic increased cholesterol biosynthesis in rats fed a cholesterol-containing diet, but had no effect in a cholesterol-free diet. Pectin slightly increased the turnover of cholesterol, but gum arabic and agar had no effect. This work supports the hypothesis that pectin lowers cholesterol levels by interfering with cholesterol absorption and by increasing cholesterol turnover. The study also suggests that complex carbohydrates differ in their effects on cholesterol metabolism. The reason for these differences remains to be determined.

Effects of monensin on in vivo rumen propionate production and blood glucose kinetics in cattle.

Abstract: Four rumen-fistulated steers (154 to 253 kg), fed two different diets in succession, were used to determine effects of monensin on rumen propionate production rates and blood glucose kinetics as determined by single-injection isotope-dilution techniques. A high-roughage and a high-grain diet, with and without 150 mg of monensin daily, were fed isoenergetically at 2-hour intervals. Monensin increased rumen propionate pool sizes from 32 to 57 g for the high-roughage diet and from 37 to 66 g for the high-grain diet and increased rumen propionate production rates from 441 to 659 g/day for the high-roughage diet and from 510 to 899 g/day for the high-grain diet. Molar percentages of rumen propionate were increased significantly by monensin in the high-grain diet. Blood glucose pool sizes were not changed significantly by either monensin or isoenergetic diets. Monensin increased irreversible losses of glucose from 582 to 677 g/day for the high-grain diet. Monensin tended to increase glucose total entry rates for both diets and to increase irreversible loss of glucose for the high-roughage diet but the differences were not significant. Thus, increases in glucose kinetics are minor in contrast to major increases of rumen propionate production caused by monensin.

Validation of the diagnostic value of plasma pyridoxal 5'-phosphate measurements in vitamin B6 nutrition of the rat.

Abstract: The relationship of plasma pyridoxal 5'-phosphate (PLP) to PLP content of tissues and activities of PLP-dependent enzymes was examined to establish its value in assessing vitamin B6 nutrition. Weanling rats were fed ad libitum for 9 weeks purified diets which supplied 0, 4, 12, 24, and 100 micrograms of pyridoxine daily. Growth increased with increasing pyridoxine intake, reaching a maximum at 24 micrograms/day. Liver and brain PLP also increased, attaining maximal values at 12 micrograms. By contrast, muscle and plasma PLP did not saturate when vitamin B6 intake was increased to 100 micrograms. Erythrocytic holoenzyme activity of aspartate (Asp) aminotransferase became maximal with 24 micrograms but that of alanine (Ala) aminotransferase did not. Hepatic holoenzyme activities of Ala, Asp and tyrosine aminotransferases reached maximal values with only 4 micrograms vitamin B6 but that of serine dehydratase became maximal with 12 micrograms. Measurement of coenzyme saturability suggested that apoenzyme degradation, coenzyme affinity and PLP transfer determine the activities of these enzymes. It is concluded that plasma and muscle PLP behave as mobilizable storage pools and that plasma PLP is a sensitive and reliable indicator of vitamin B6 nutrition.

Tryptophan and Threonine Requirements of Fingerling Channel Catfish

Abstract: Growth studies, utilizing a 24% crude protein diet containing an amino acid pattern similar to whole egg protein, indicate that the tryptophan requirement for fingerling channel catfish (Ictalurus punctatus) is about 0.12% of the diet (dry weight basis) or 0.5% of the dietary protein. Similar studies indicate that the threonine requirement for the same fish is about 0.53% of the diet (dry weight basis) or 2.21% of the dietary protein. The dietary requirement of threonine was confirmed by serum free threonine analysis. A marked increase in serum free threonine occurred at a dietary threonine level of approximately 0.5% of the diet. None of the gross pathological changes previously reported for tryptophan deficiency in sockeye salmon and rainbow trout were observed in channel catfish.

Vitamin E, antioxidants and lipid peroxidation in experimental atherosclerosis of rabbits.

Abstract: The purpose of this study was to evaluate the effects of large amounts of dietary vitamin E and butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in rabbits fed a low-cholesterol, atherogenic diet, and to seek for evidence of lipid peroxidation in the atherosclerotic lesions. Rabbits were fed a purified atherogenic diet, containing butter or the basal diet supplemented with either 1.0% of vitamin E or 0.1% each of BHA and BHT for periods up to 3 years; a negative control group was fed the basal diet with corn oil replacing butter. Aortic and coronary atherosclerosis were more frequent and extensive in rabbits fed either the basal diet or the basal diet supplemented with BHA and BHT than in rabbits fed either the basal diet supplemented with vitamin E or the negative control diet. Dietary vitamin E inhibited atherogenesis by preventing hypercholesterolemia. No evidence of lipid peroxidation was detected in the arterial lesions.

The branched-chain amino acid antagonism in chicks.

Abstract: The effects of dietary supplements of branched-chain amino acids on growth, food consumption and metabolism in chicks were investigated. When an adequate diet contained 1.20, 1.60, 2.25, 3.75, or 5.00% leucine, increasing leucine content caused reduced food consumption and weight gains, coupled with impaired efficiency of food utilization. When the diet deficient in branched-chain amino acids contained 0.98, 1.46, 2.25, 3.75, or 5.00% leucine, increasing leucine resulted in increased food consumption and reduced efficiency of food utilization when levels of leucine up to 3.75% were fed. Excess leucine depressed plasma concentrations of isoleucine and valine. Excesses of isoleucine or valine caused smaller depressions of concentrations of the other two branched-chain amino acids. All these effects were seen during the first 8 days of experiment, after which they diminished or disappeared. Muscle branched-chain amino acid aminotransferase (BCAT) (L-leucine:2-oxoglutarate aminotransferase, EC 2.6.1.6) activity was increased in chicks fed excess leucine but not in those fed excess isoleucine or valine. Hepatic alpha-ketoisocaproic dehydrogenase (KADH) (2-oxoisocaproate:lipoate oxidoreductase, EC 1.2.4.3) activity and muscle polyribosomal aggregation were unaffected by diet. When chicks were fed diets containing either 0.98 or 2.25% leucine, production of 14CO2 from [1-14C]isoleucine and [1-14C]valine was increased in chicks fed the higher level of leucine. The increase was small in both cases, representing approximately 2% of consumed isoleucine and valine. Increased production of 14CO2 was observed within 12 hours of feeding excess leucine; however, BCAT increased only after 2 to 4 days. No differences were seen in excreted 14C or in the relative distribution of 14C along the small intestine. We conclude that the chick is able to adapt in part to excesses of dietary leucine and that the branched-chain amino acid antagonism may involve increased catabolism of the limiting branched-chain amino acids.

The Effects of Fasting on Body Composition, Glucose Turnover, Enzymes and Metabolites in the Chicken

Abstract: [2-3H] or [6-3H]glucose injected simultaneously with [U-14C]glucose re mained constant with fasting at 10 to 13 mg/minute/kg body weight which is much higher than reported for mammals. Blood lactate and glycerol were unchanged with fasting, while pyruvate increased and plateaued. Plasma alanine, serine and glycine levels were extremely high compared to values in fasted mammals. Blood /3-hydroxybutyrate increased dramatically with fasting (350 to 3,500 nm/ml), while acetoacetate remained constant. The hepatic lactate :pyruvate ratio was unchanged with fasting, while the /3-hydroxybutyrate :acetoacetate ratio increased. These ratios have been reported to influence phosphoenolpyruvate (PEP) and glucose production in mammals. Hepatic and renal phosphoenolpyruvate carboxykinase (PEPCK) levels remained constant, while hepatic lactate dehydrogenase increased with fasting. AŸ-Hydroxybutyrate dehydrogenase levels were very low at all times. The results indicate little glucose sparing adaptation per kg in the fasting chicken. J. Nutr. 108: 648-657, 1978.

Copper deficiency in the laying hen.

Abstract: Copper deficiency in the laying hen resulted in anemia and the production of eggs which were abnormal in size and shape. Many of the eggs had shells which were wrinkled and rough in texture. There was also an increase in the number of shell-less eggs. Examination of malformed egg shells using the scanning electron microscope revealed ultrastructural changes in the mammillary layer of the shell. The effect of copper deficiency on shell formation was attributed to the shell membranes which were altered in color, appearance, and physical consistency. Amino acid analysis of the membranes indicated that the membranes from copper deficient hens were characterized by an increase in lysine content. This suggests that copper is necessary for the formation of lysine derived cross-links in a manner similar to that which occurs in connective tissue. The exact nature of these cross-links is unknown at this time.

Heat increment associated with dietary protein, fat, carbohydrate and complete diets in salmonids: comparative energetic efficiency.

Abstract: The heat increment (HI) of feeding, which is the increased heat production following consumption of food by an animal, accounts for as much as 30% of the ingested metabolizable energy (ME) in mammals and birds. The purpose of these experiments was to measure the HI associated with the feeding of a complete diet and purified fat, protein, and carbohydrate to salmonids. Measured amounts were fed and the heat production was measured by direct calorimetry. Increased heat production was observed about 30 minutes after feeding and remained elevated for 1 to 5 hours, depending on the amount and type of material fed. The HI of protein was much lower with fish than with mammals and amounted to less than 5% of the ingested ME. The HI's of carbohydrate and protein were not significantly different from each other but both were higher than fat. The HI, when complete diets were fed, was less than 3% of the ME. The net energy of protein is higher for fish than for birds or mammals. A major part of the superior energetic efficiency of fish is due to the low energy cost of protein metabolism.

The Role of Transamination in Methionine Oxidation in the Rat

Abstract: The role of transamination as the initial step in catabolism of methionine in the rat was investigated. [Methyl-14C] or [1-14C]-L-Methionine was added to tissue homogenates and transamination was determined from the counts recovered in a precipitable phenylhydrazone following treatment of the samples with 2,4-dinitrophenylhydrazine. Transamination of methionine was detected in homogenates of liver, kidney, heart, brain, spleen, skeletal muscle, and small intestines. The product of methionine transamination in the liver was identified as alpha-keto-gamma-methiolbutyrate. Approximately the same tissue distribution was observed for the conversion of the methyl or carboxyl carbon of methionine or alpha-keto-gamma-methiolbutyrate to CO2. alpha-Keto-butyrate could be used as a co-substrate for transamination, but inhibited oxidation of methionine apparently by competing for oxidation of alpha-keto-gamma-methiolbutyrate. S-Adenosyl-L-methionine was not a substrate for transamination in the liver homogenate system nor did it inhibit transamination of methionine. Amino-oxyacetic acid inhibited transamination and oxidation of methionine, but not oxidation of alpha-keto-gamma-methiolbutyrate. These observations are consistent with transamination being an initial step in methionine catabolism and an alternate pathway for methionine oxidation which does not involve its activation to S-adenosyl-L-methionine.

Effects of force-feeding and dietary cellulose on liver lipid accumulation and lipid composition of liver and plasma in growing chicks.

Abstract: Changes of content and composition of lipid in liver and plasma affected by force-feeding and dietary cellulose were investigated in 14-day old Single-Comb White Leghorn male chicks. They were given a purified high energy diet (starch-casein diet without fiber) supplemented with or without dietary cellulose. Chicks were fed ad libitum or force-fed the experimental diet. Force-feeding of excess food improved the growth rate of chicks and feed efficiency, but feeding of cellulose did not affect body weight gain and feed efficiency, though a slight improvement in nitrogen retention was observed. Liver weight and lipid content in liver and plasma were markedly elevated by force-feeding, and were markedly depressed by dietary cellulose in the force-fed chicks. It is suggested that changes of liver lipid by force-feeding and dietary cellulose are mainly originated from the changes of triglyceride in the liver lipid. No marked changes were observed in fatty acid composition of abdominal fat and liver lipid in the cellulose-fed chicks. These results suggest that dietary cellulose may affect lipid metabolism in growing chicks.

Models of infantile undernutrition in rats: effects on milk.

Abstract: Although there are at least six commonly used methods for producing malnutrition in suckling rat pups, no attempt has been made to determine the quality of the nutrients available to the pups in each of these methods. In the present study, milk composition was determined for each of these methods and related to maternal nutritional status. These methods were: 1) large litters were fostered on the dams; 2) the dams were fed low protein diets; 3) the dams were fed a reduced amount of good quality diet; 4) and 5) the pups were removed from the dams and kept 4) with a non-lactating female or 5) in an incubator for half of the day; and 6) some of each dams' teats were destroyed. Maternal nutritional status was affected only in the cases where the dams' diet was deficient (methods 2 and 3), producing weight loss and lowered hematocrits in both cases and lowered serum protein when the low protein diet was fed. The low protein diet condition resulted in a lower nitrogen content and an elevated total fat content of the mild. It was concluded that previous consideration of all of the above methods as equivalent in terms of the quality of the milk produced is not justified.

Taurine deficiency in the kitten: exchange and turnover of [35S] taurine in brain, retina, and other tissues.

Abstract: Kittens fed a purified diet containing partially-purified casein as the source of protein become taurine-deficient and develop retinal degeneration. The present studies report the exchange and turnover of taurine in different areas of brain, retina and other tissues and fluids of control and taurine-deficient kittens. The various tissues and fluids have different rates of exchange and different half-lives of taurine; taurine deficiency causes a range of changes in these parameters. Generally, tissues and fluids from taurine-deficient kittens accumulated more [35S] taurine and had a longer half-life of taurine than tissues and fluids from control kittens. Nine areas of brain were studied and, of these areas, olfactory bulb had the greatest concentration of taurine. Olfactory bulb resisted taurine depletion to a greater extent than other areas; and, in contrast to other areas of brain, in taurine-deficient kittens, it accumulated [35S] taurine for most of the experiment. Retina resisted taurine depletion and, in taurine-deficient kittens but not in control kittens, it accumulated [35S] taurine throughout the experiment. The amount of taurine conjugated to bile acids was unchanged by the taurine depletion, but the kinetic behavior was altered and was similar to that of retina. The results provide support for the suggestion that, in the kitten at least, taurine is most important for the functions of bile and retina and that taurine depletion affects retina before bile. Taurine may have special importance in olfactory bulb but not necessarily in other regions of brain.

Effect of level of feed intake on lactate and acetate metabolism and lipogenesis in vivo in sheep.

Abstract: Experiments were conducted to investigate the relative importance of acetate and lactate as precursors for fatty acid synthesis in vivo in sheep fed ad libitum (3.3 Meal of metabolizable energy (ME)/ day) or a restricted level of feed intake (1.7 Meal of ME/day). Tritiated water (3H2U) was also used to estimate fatty acid synthesis from all carbon precursors rather than from a specific carbon precursor. In experi ment 1, the amount of tritium (3H) incorporated into adipose tissue fatty acids increases with time up to 6 hours after intravenous 3H2O injection in perirenal, mesenteric, omental, shoulder, rump, backfat and abdominal adipose tissue from ad libitum fed sheep. The rate of incorporation did not differ significantly between tissue sites. The 3H2Oequilibrated rapidly with body water and the plasma 3H;ÂiO specific activity did not change signifi- cantA¬y for 3 hours after 3H^.Oinjection. Plasma acetate turnover rate was not influenced by ad libitum versus restricted feeding and averaged 2.99 ± 0.28 mmole/hour/kg of body weight. Plasma lactate turnover was decreased significantly in restricted versus ad libitum fed sheep and averaged 0.99 ± 0.01 and 1.76 ± 0.07 mmoles/hour/kg of body weight, respectively. Re stricting feed intake for 14 days decreased the total weight of perirenal, mesenteric, and omental adipose tissue masses compared to ad libitum fed sheep. Total 3H incorporated into fatty acids in restricted fed sheep was only 11% to 13% of that in the ad libitum fed sheep in perirenal and omental adipose tissue; treatment differences in 3H incorporation were much smaller in the total carcass adipose tissue. On the basis of the ("CJlipid relative specific activity, lactate was incorporated into carcass adipose tissue fatty acids at 38% of the rate for acetate in ad libitum fed sheep and only 16% and 21% of the rate for acetate in perirenal and omental adipose tissue. Lactate appears to have been more important as a lipid precursor in ad libitum fed than in restricted fed sheep. J. Nutr. 108: 926-935, 1978.

Zinc absorption and metabolism by isolated, vascularly perfused rat intestine

Abstract: An isolated vascularly perfused rat intestine system was utilized to examine various aspects of zinc absorption in an attempt to more clearly examine the mechanisms involved. The lumen was perfused with a modified tissue culture medium containing 65Zn. The vascular system was perfused from the superior mesenteric artery to the portal vein, with Krebs-Ringer bicarbonate buffer containing 5% rat serum. The criterion for absorption was the amount of radioactivity transferred to the vascular perfusate. When the intestines were obtained from rats that had consumed a zinc-deficient diet the amount of zinc absorbed increased markedly. Conversely, elevation of zinc status decreased the amount of 65Zn that could be transferred to the vascular perfusate. These data strongly suggest that the isolated, perfused rat intestine retains the ability to exercise homeostatic control over 65Zn absorption. Transfer of infused 65Zn to the vascular perfusate was significantly decreased by aspirin, phytate, and prostaglandin E2. Uptake of 65Zn from the lumen into the intestinal cells was significantly increased by histidine and significantly decreased by phytate and prostaglandin E2. Thus, the isolated, vascularly perfused rat intestine appears to be capable of differentiating between the cellular uptake and cell to plasma transfer phases of zinc absorption.

Threonine Metabolism in Vivo: Effect of Threonine Intake and Prior Induction of Threonine Dehydratase in Rats

Abstract: The metabolic fate of threonine was investigated in young male rats fed 15% amino acid diets containing from 0.15% to 0.85% of L-threonine. Liver serine-threonine dehydratase (S-TDH) activity did not increase with increasing dietary threonine content. The level of threonine required for maximum weight gain was not greater than 0.55% of the diet (or about 600 mumoles/day). Tissue free threonine content of rats fed the diets with 0.15% or 0.3% of threonine was very low but increased sharply with increasing dietary threonine content above 0.3%. During ad libitum feeding of these diets containing L-[U-14C]threonine, rate of oxidation of threonine was low when intake was in the range of the requirement for maximum growth, but increased, thereafter as threonine intake increased. A 30-fold induction of liver S-TDH, by prior feeding of an 80% casein diet, did not result in increased oxidation of threonine when dietary threonine content was 0.15%. When dietary threonine content was increased to 0.5%, oxidation of threonine increased slightly but significantly. With 3% of threonine in the diet, rats previously fed a 15% casein diet had extremely high tissue threonine concentrations whereas those with high S-TDH activity, due to the previous feeding of the 80% casein diet, oxidized threonine rapidly and tissue threonine concentrations were elevated much less.