Gastric proteases in the human infant.

The electrophoretic mobilities of proteases present in gastric juice taken within 10 h of birth from 5 healthy, premature infants were compared with calf chymosin, pig pepsin A and human adult gastric juice. The juice from 2 infants contained predominantly a chymosin-like enzyme, another had almost exclusively pepsins similar to those of the adult juice, while the other two contained a mixture of both. The pepsins consisted of two elements, probably pepsin A (EC 3.4.23.1), and pepsin C (EC 3.4.23.3). Single radial immunodiffusion gave a definite reaction to calf anti-chymosin serum in five samples taken from a further 17 infants. These results indicate that some human infants secrete chymosin. The reaction in the immunodiffusion assay indicated a much lower enzyme activity than that implied from electrophoretic separations. It is suggested that species differences resulted in poor cross-reactivity of the antiserum.

Growth, digestion, and protein metabolism in neonatal pigs given diets containing whey as the predominant or only source of milk protein.

Milk substitutes containing ratios of casein/whey protein ranging from 80:20 to 0:100 were given to neonatal pigs. A ratio of 60:40 gave maximum growth rate, efficiency of feed utilization and nitrogen retention, and the lowest concentration of urea in blood plasma. This ratio is close to that in sow's milk, suggesting the hypothesis that in each species the milk may be adapted to the protein requirements of their young; by analogy, a casein/whey protein ratio of 20:80 in humanized milk formula might lead to more efficient protein utilization by the infant. In general, changes in the proportion of casein and whey proteins in the diet produced similar effects on the free amino acids in blood plasma as were found in clinical studies reported in the literature, providing further evidence of similarities in the protein metabolism of infants and neonatal pigs. The amount of nitrogen in the digesta remaining in the stomach at 1 h after a meal indicated that whey proteins empty from the stomach more rapidly than casein.

Evaluation of the neonatal pig as a model for infant nutrition: effects of different proportions of casein and whey protein in milk on nitrogen metabolism and composition of digesta in the stomach.

Neonatal pigs were evaluated as a model for protein metabolism of infants. Milks were given in which the protein (15 or 30 g/liter) was supplied by casein and whey in the proportions of 80:20 or 40:60. Severe or moderate restriction of feed intake was also compared. Whey-predominant milks reduced the concentration of urea N in blood plasma and the proportion of urea N in urinary total N. These effects are consistent with most previously reported data from infants, particularly those of low birth weight. The efficiency of N retention was improved at the higher concentration of dietary protein. Whey-predominant milks also reduced the amount of N retained in the stomach. The magnitude of some of these effects was influenced by the level of feed intake. Total N retention reflected protein intake but was not affected by protein source. N retention determined by a balance procedure exceeded that calculated from carcass analysis, but the effect of protein intake was similar from either procedure.

Trace-nutrient-binding proteins in milk and the growth of bacteria in the gut of infant rabbits.

1. The influence of trace-nutrient-binding proteins on the growth of coliforms, streptococci and lactobacilli in the gastrointestinal tract was examined in neonatal rabbits delivered germ-free and dosed with an artificial flora (ESL), or born conventionally and dosed with ESL or rabbit faeces. 2. In the stomach and small intestine of both gnotobiotic and conventional animals the counts of coliforms were usually atypically high and those of streptococci were always low. In the colon the counts of coliforms and streptococci were high. Lactobacilli usually became established in the gut of the gnotobiotic animals but were not found in the conventional rabbits. 3. Sterilization (freeze-drying followed by gamma-irradiation) of the milk decreased its capacity to bind added iron by 45% and vitamin B12 by 30%. When compared with raw milk, feeding of radiation-sterilized milk did not affect the viable count of coliforms and streptococci in the gut of gnotobiotic animals. 4. Saturating the nutrient-feeding proteins in milk with Fe, folic acid and vitamin B12 had no effect on the numbers of coliforms, streptococci and lactobacilli recovered from the intestine.

The effects of pregnancy and lactation on the activities of trypsin and alpha-chymotrypsin in the rat pancreas.

1. The food intake, pancreas weight and trypsin (EC 3.4.21.4) and alpha-chymotrypsin (EC 3.4.21.1) activities in the pancreas were measured in rats during pregnancy and lactation and after the young were weaned. 2. All the quantities measured increased significantly during lactation and had returned to their original values by 4 weeks after weaning. Food intake and pancreas weight were highest after the second week of lactation. Total trypsin and alpha-chymotrypsin activity, and the activity per g tissue, fell during pregnancy and rose during lactation, reaching a maximum 1 week after weaning. 3. From these and other results it is suggested that the hypertrophy and hypersecretion of pregnancy and lactation are initiated by changes insulin secretion and mediated by the trophic effects of gut hormones, and that differences in the nature and timing of the response may be controlled by nutrient availability.

Absence of immunological hypertensitivity to dietary cow's-milk proteins in infant rabbits.

1. Rabbits hand-reared on a diet based on cow's milk frequently experience convulsive and sometimes fatal reactions to their feed. These have been thought to be caused by immunological hypersensitivity to cow's milk. 2. This explanation has been re-examined and found to be untenable.

The modified anaphylaxis hypothesis for cot death. Anaphylactic sensitization in guinea-pigs fed cow's milk.

Guinea-pigs on a normal diet, but given cow's milk to drink instead of water, very soon became anaphylactically sensitive to cow's milk and may be fatally shocked following either i.v. injection or intratracheal inhalation of cow's milk.