FURTHER STUDIES OF THE CALCIUM CONTENT OF THE BODY AS INFLUENCED BY THAT OF THE FOOD

325. A study of the balance of certain milk nutrients in the making of Cheddar, Cheshire and Stilton cheeses, and of their fate during the ripening of the cheeses

1. Cheshire, Cheddar and Stilton cheeses were made on one occasion from winter, and on another from summer, milk.

2. The distribution of vitamin A and carotenoids, vitamin B1, riboflavin and vitamin C between milk, whey and curd was measured during cheese-making.

3. The fate of these vitamins during ripening was determined.

4. Some 80% of vitamin A and carotene, 15% of vitamin B1and 25% of riboflavin originally present in milk were recovered in the green cheese and persisted throughout ripening.

5. Vitamin C disappeared progressively during cheese-making and was absent from the cheeses.

6. Vitamin B1and especially riboflavin were recovered in cheese in larger proportions than would be expected from the partition of water between curd and whey, indicating that they were partly present in milk in combination with the coagulable solids.

Physiologically based models for bone-seeking elements. I. Rat skeletal and bone growth

A review of features of bone structure and bone growth critical to the development of a physiologically based model of the whole-body kinetics of bone-seeking elements is presented. Allometric equations describing the volume and weight of the bone, bone marrow, and skeleton during growth of the rat from birth to maturity are derived. Weights of body calcium and bone ash are also expressed allometrically as functions of body weight during growth. The simplicity of these functions will allow them to form the basis of a flexible model of the movement of bone-seeking elements in and out of bone. Blood flow rates to bone and bone marrow are incorporated into the model of the mature skeleton. The predictions of the skeletal growth model are in good agreement with measured quantities of bone, skeletal ash, and calcium in growing rats.

Effect of level of dietary calcium on the skeleton of the rat

1. The total body calcium (Expt 1) of litter-mate male rats given a diet adequate in phosphorus and high (0·74%) or low (0·13%) in Ca from the age of 3 weeks was determined after 21, 48 and 60 weeks on the diet. In Expt 2, the ash content of ten groups of bones from 10-week-old rats given these same diets for 7 weeks was studied to ascertain whether all groups were equally affected by the difference in dietary Ca level. Four groups of bones, i.e. skull and mandibles, vertebras, the shafts and the ends of long bones, were consequently chosen for examination in Expt 3 where their growth and composition were studied in rats given the Ca diets for 24, 48 or 60 weeks from the age of 3 weeks.

2. Total body Ca (Expt 1), expressed as g Ca or as a percentage of the net body-weight or of net dry, fat-free carcass weight, was always significantly higher in rats given the higher level of Ca. The dietary effect was greatest after 21 weeks.

3. The higher level of dietary Ca led to a highly significant increase in the weight of the dry, fat-free bone and in the percentage ash content of all ten bone groups after 7 weeks (Expt 2). The greater treatment differences in ash content occurred with the less well mineralized bones.

4. In Expt 3, irrespective of diet, the four groups of bones developed at different rates. In rats given the diets for 24 weeks or longer, the vertebras and the shafts of long bones showed the greatest proportional increase in weight of dry, fat-free bone and ash relative to the corresponding values for 3-week-old rats; the greatest change in percentage ash content occurred in the ends of the long bones.

5. Increasing the level of Ca in the diet increased the weight of the dry, fat-free bone and its ash content. The effect of diet decreased with increasing time on the diets, in general persisting most strongly in the skull and mandibles and declining most rapidly in the ends of the long bones. The percentage Ca and P content of the bone ash was only slightly affected by diet and, except for the Ca in the ash of vertebras, significant differences were only found in the composition of the ash of bones from 27-week-old rats.