Showing papers in "Journal of Nutrition in 1965"

Amino Acid Diets and Maximal Growth in the Rat

Abstract: Amino acid diets fed in an agar gel have been found to support weight gains of rats as great or greater than those obtained with diets containing an equiva lent quantity of casein supplemented with methionine. Over 1% arginine, 0.6% asparagine and feeding the diet in gel form were necessary to obtain maximal weight gain. The diet contained amino acids in excess of the requirements of the rat, and hence it should be possible to improve the efficiency of utilization of the amino acid mixture. It was not until after the extensive in vestigations of Rose and co-workers had culminated in the discovery of threonine that amino acid diets of known composi tion could be prepared which would sup port growth. At the close of their work, Rose and associates (1) had developed amino acid diets that would support a moderate rate of growth but not a rate equivalent to that obtained with diets con taining intact protein. When it was ob served that intact protein increased weight gain of animals fed amino acid diets, the growth-stimulating factor was for some time considered to be peptide in nature. For example, Woolley (2) observed that a supplement of 2% of casein improved the growth of mice fed an amino acid diet and attributed the increased growth rate to a peptide growth factor which he isolated from enzymatic digests and designated strepogenin. A few years later Maddy and Elvehjem (3) reported equivalent growth rates for mice fed whole casein or an amino acid diet. Still later, however, (1952) Maddy and Swift (4) were not able to achieve maximal weight gains in rats fed amino acid diets. The quantity of protein required in amino acid diets for maximal growth of the rat is in fact, large. In table 1 are listed the weight gains of rats fed a complete amino acid diet, supplemented with in creasing increments of casein. Twelve per cent of casein was required before weight gain was equivalent to that of rats fed a diet containing 20% casein. (The amino acids in the diet did not prevent maximal weight gain from being attained.) From the late 1940's until the present there has been considerable controversy over the question of whether there is a specific compound in protein which in creases the growth rate of animals fed an amino acid diet. There have been several reports that amino acid diets supported growth rates equivalent to these obtained with diets containing intact protein and an even greater number indicating that protein would stimulate the growth of rats fed amino acid diets. An examination of the literature indicates that maximal growth rate has, in fact, never been ob tained routinely. One question has been the importance of using only the L-isomers of amino acids as compared with adding appreciable quantities of u-amino acids to the diets.

Tumor incidence patterns and nutrition in the rat.

Abstract: Levels of caloric and of protein intake were demonstrated to have a modifying influence on tumor incidence patterns in the male rat. The 5 uniform life long dietary regimens used differed only in allotments and intakes of protein (casein), carbohydrate (sucrose) or of total calories. Age-specific rate tables and tumor in cidence ratios aided in assessment of the nutritional effects. Total tumor risk was directly and exponentially related to caloric intake, but time differences for develop ment of each of the incidence patterns were related inversely to caloric intake. Among all the groups tumor incidences formed an exponential continuum when related to growth rate in early life and mature body weight. Within each dietary group, rats of heavier weight had greater tumor risk than lighter rats. Occurrence, the proportional incidence and the malignancy of certain tumors correlated with the level of protein intake. Malignant lymphomas were predominant in rats with high protein intake, whereas fibromas and fibrosarcomas predominated in rats with low protein intake. Tumor incidence patterns differed quantitatively, qualitatively or both. Thus, in 2 groups with identical caloric intake, risk for all tumor types was similar but the group with higher protein had a greater risk for malignancy. Rate patterns for benign tumors, but not for malignant tumors, were dependent upon the mortality rate patterns of their re spective populations. Lowest incidence, greatest delay in time of occurrence, absence of malignant epithelial tumors and greatest life expectancy, were observed when in takes of protein, carbohydrate and total calories were low. Different nutritional regimens affect the prevalence of many age-associated dis eases, the life span of the individual and, as a result, mortality patterns of a popula tion. A multidiscipline study, of which some aspects are presented here, was de vised to assess the influence of diet upon degenerative disease and mortality in the rat. Particular emphasis was placed upon the chronological sequence of biochemical, biological and pathological events and processes over the entire life span. The interrelationships among diet, age and hepatic enzyme activity (1-6) suggested that the enzyme activity levels and pat terns were related to processes of ageing and that modification of the rate of change of these and other tissue constituents by nutritional means would result in changing patterns of mortality and disease. It was learned that length of life was influenced not only by the degree of dietary restric tion but also by change in the ratio of the protein and carbohydrate components of the diets (7). The shortest life expect ancy was observed to be associated with the highest incidence of glomerulonephroJ. NUTRITION, 87: '65 sis, a condition noted commonly in rats fed a commercial diet ad libitum, whereas the greatest life expectancy and the lowest incidence of kidney lesions were found among rats whose intakes were low in pro tein, carbohydrate and calories (8). The influence of long-term caloric re striction in reducing the incidence of tu mors is well documented for the rat and the mouse (see reviews by Rusch (9), Tannenbaum and Silverstone (10), and White (11)). Experimental studies of the influence of diet on tumorigenesis have, for the most part, been concerned with induced or transplanted tumors, or with highly inbred mice predisposed to specific tumor types. In the rat, certain deficiencies have been shown to result in the appear ance of specific tumors not normally ob served in the strain of rats used, or to pro duce an increase in the incidence of spe cific tumors. The most notable of these Received for publication February 8, 1965. i This investigation was supported in part by Public Health Research Grants HD 00490 and HD 00086 from the National Institute of Child Health and Human

Absorption of calcium and phosphorus along the gastrointestinal tract of the laying fowl as influenced by dietary calcium and egg shell formation

Abstract: The apparent absorption of calcium, phosphorus and total dry matter along the gastrointestinal tract of the laying hen, was followed using yttrium-91 as a non-absorbed tracer. Percentage calcium and phosphorus absorption appeared to be greater in the proximal parts of the intestine than in the distal parts. This differ ence was smaller for total dry matter. Percentage calcium absorption was not signifi cantly influenced by its dietary level, nor did the latter influence the absorption of dry matter. Percentage absorption of phosphorus was, however, depressed by the higher dietary calcium level. Egg shell deposition was associated with increased calcium and to a smaller degree, phosphorus absorption. It did not influence dry matter ab sorption. A heavy endogenous phosphorus excretion was observed in the duodenum. The identification of the sites of mineral absorption is important for understanding the mechanism involved in the mineral absorption. This problem was studied mainly by in vitro and in situ experimenta tion. The in vitro studies such as those of Schachter and associates (1, 2) provide information on the capacity of various intestinal segments to absorb calcium. However, the rate and percentage of cal cium absorption may also depend on the rate of passage of food, which is quite variable in the various intestinal segments (3, 4). Therefore, in vitro methods can not measure the relative contribution of each segment to total calcium absorption in vivo. A different method for studying calcium absorption is the use of oral doses of 45Caor its injection into different parts of the intestine (5, 6). This method, how ever, measures mainly the outflux of cal cium from the intestine and not the net absorption which is the difference between the outflux and the influx. Chandler and Cragle (7) used I44Ceas a non-absorbed tracer to study calcium and phosphorus absorption in calves. The ratio of calcium and phosphorus to 144Ceat any point in the intestine measures the cumu lative percentage absorption up to this point. Similarly, Bolton (8) used cellulose as a tracer for estimation of protein and available carbohydrate absorption along the tract of chickens. Marcus and Lengemann (3) reported that 81Ywas not ab sorbed in the rat. Preliminary trials in this laboratory showed that this isotope was not absorbed by colostomized chickens. Following an oral dose of 91Ymixed in some feed, 93% of the dose was detected in the feces voided during the first 24-hour period, and 3% in the following 24-hour period. No activity could be detected in the urine of these animals. Therefore, 91Ywas used in the present trial to follow the absorption of calcium and phosphorus along the intestinal tract of laying hens. The possibility that dietary calcium and the presence of a calcifying shell in the uterus may modify the pattern of calcium and phosphorus absorption was also investigated.

Dietary regulation of pancreatic enzyme synthesis, secretion and inactivation in the rat.

Abstract: Dietary regulation of the synthesis, secretion and inactivation of trypsin, chymotrypsin and amylase was studied in rats fed a nitrogen-free ration or diets containing casein, whole-egg protein or hydrolysates of these proteins. Meas urements of the enzyme content of the pancreas after an 11-hour fast showed that substitution of the nitrogen-free diet for the casein diet depressed synthesis of the 3 enzymes, whereas replacement with whole-egg protein usually increased synthesis of trypsinogen and chymotrypsinogen but not amylase. Relatively more of the amino acid supply of the pancreas was diverted to chymotrypsinogen and less to amylase when whole-egg protein was fed. The reverse was true when casein was given. Rats fed the nitrogen-free diet synthesized relatively more trypsinogen. With respect to trypsino gen and chymotrypsinogen, the secretory response elicited by hydrolyzed casein and hydrolyzed egg protein was similar to the one evoked by casein. However, hydrolyzed egg protein was not equivalent to whole-egg protein. Interpretation of these results is based on the premise that dietary protein regulates pancreatic enzyme synthesis, in part, through amino acid pool(s) in the pancreas. The observation that the nitrogen- free diet retarded the rate of inactivation of amylase more than did the protein or hydrolyzed protein diets may be related to a protective effect of starch which was included in the nitrogen-free diet. The results of previous studies suggest that dietary proteins influence the tryptic, chymotryptic and amylolytic activities of

Magnesium Requirement of the Baby Pig

Abstract: The magnesium requirement of baby pigs receiving a purified caseinglucose diet containing 0.8% of Ca, 0.6% of P and 1800 IU of vitamin D3/kg was studied in two 5-week trials using levels of dietary Mg from 25 to 825 ppm. Pigs receiving less than 125 ppm of Mg exhibited poor growth, poor food utilization, weak ened pasterns, stepping syndrome, tetany and death. Pigs receiving 125 ppm of Mg exhibited all of these symptoms except tetany and death. Pigs receiving 225 ppm of Mg or more exhibited no overt symptoms of magnesium deficiency. Serum and bone Mg concentrations were reduced in all pigs receiving 225 ppm or less of dietary Mg. Values of serum Ca and Mg concentration were significantly related. Values of serum and bone Mg concentration were also positively related. A dietary Mg level of 325 ppm was adequate to meet all criteria and under the conditions of this study is judged to be the minimal magnesium requirement of the baby pig. Studies by Mayo et al. ( 1) with pigs weaned at 3 and 9 weeks of age indicated magnesium requirements for maximal growth rate of 334 and 241 ppm, respec tively, and 400 and 505 ppm, respectively, for the prevention of deficiency symptoms. On the basis of balance studies with pigs 3 to 5 weeks of age, Hartley et al. (2) recommended a dietary magnesium con centration of 400 ppm. Estimated mag nesium requirements of 400 and 505 ppm are listed by the NRC (3) and Lucas and Lodge (4), respectively, for pigs weighing over 4.5 kg. Studies have not been reported of determinations of the magnesium re quirement of pigs weaned prior to 3 weeks of age. The present studies were conducted to determine the magnesium requirement of baby pigs weaned at one day of age and reared with a purified diet. Criteria of dietary magnesium adequacy were similar to those used in previously reported studies of mineral requirements (5-7). MATERIALS AND METHODS Two trials were conducted using 36 Yorkshire-Hampshire crossbred pigs of either sex. Pigs were taken from the sow during the first day of life and reared in individual metal cages. Adjustment of the pigs to a purified diet in dry meal form was facilitated by means described earlier (7) and pigs were assigned to experimen tal levels of dietary magnesium at one week of age. The purified diet was very similar to that used in earlier studies (7) and distilled water was measured and sup plied ad libitum as the only source of drinking water. This seemed advisable be cause the magnesium concentration in tap water at our laboratory is about 25 ppm and the distilled water contained less than 1 ppm. The purified diet consisted of 30% of casein,3 5% of lard, 5% of cellu lose,4 54% of glucose,5 6% of minerals (table 1) and vitamins (8). During the final 2 weeks of each of the 5-week trials, casein was reduced to 20% of the diet and glucose was increased to 64% of the diet. Dietary calcium and phosphorus levels were maintained at 0.8 and 0.6% , respec tively, by adjusting the mineral mixture ingredients as shown in table 1. The basal purified diet contained 25 ppm of mag nesium and supplemental levels of zero, 100, 200 and 400 ppm of magnesium were supplied in the first trial and 50, 200, 300, 400 and 800 ppm of added mag nesium in the second trial. All suppleReceivedfor publicationJuly 30, 1964. 1Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal article no. 3434. 2Presented in part before the meeting of the American Society of Animal Science, Chicago, Novem ber, 1962 (J. Animal Sci., 21: 1006, 1962, abstract). 3 "Vitamin-Free" Test Casein, General Biochemicals, Inc., Chagrin Falls, Ohio. 4Solka Floe, Brown Company, Berlin, New Hamp shire. 5Cerelose, Corn Products Company, Argo, Illinois. J. NUTRITION, 85: '65 13 Downloaded from https://academic.oup.com/jn/article-abstract/85/1/13/4777638 by Washington University in St. Louis user on 02 July 2018 14 E. R. MILLER AND OTHERS