SUMMARY A study was made of the effect of two antioxidants, butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT), with variation in the type and quantity of dietary fat, on growth, food consumption, reproduction, mortality, organ weights and post‐mortem pathology of the rat. The normal cellular behaviour of experimental animals fed diets containing one hundred times the amount of the antioxidant normally expected to be present in human foods (normal testing dose, NTD), is the conventional yardstick of non‐toxicity. The NTD of BHA produced no apparent changes in any of the parameters measured. When BHT was fed at a dietary level of 0·1 p.c. (the NTD) in conjunction with a 20 p.c. lard supplement, it significantly reduced the initial growth rate and mature weight of male rats. No such significant effect was noted in female rats or in male rats with a 10 p.c. lard supplement. A paired feeding experiment showed that this inhibition of growth was a direct toxic effect of BHT and could not be explained by a reduction in the palatability of the diet. At the NTD, BHT produced a significant increase in the weight of the liver relative to the body weight. The mean absolute weight of the liver was also increased. A significant loss of hair on the top of the head occurred in animals whose diet contained the NTD of BHT. This effect was only noted in animals under conditions of increased stress and was enhanced by an increase in the lard content of the diet. Anophthalmia occurred in 10 p.c. of the litters born of parents fed BHT. Even when present in the diet at a concentration of 0·5 p.c., BHA and BHT had no effect on one reproductive cycle of the rat, or the histology of the spleen, kidney, liver, testes or skin, or the ratio to total body weight of the weight of the heart, spleen and kidney. If the conventional NTD be accepted, BHA fulfilled the requirements of non‐toxicity. BHT, at the NTD, on the other hand, produced deleterious deviations from normal cellular behaviour which cast doubt on the advisability of permitting this antioxidant in foodstuffs for human consumption.

Erythrocyte and plasma potassium, magnesium, sodium and calcium were estimated before and after dialysis in 32 studies on 14 patients undergoing recurrent haemodialysis. Predialysis erythrocyte magnesium was raised while sodium and calcium were depressed. Erythrocyte potassium varied depending on the total body potassium status of the patient. During dialysis erythrocyte potassium and magnesium fell but sodium and calcium increased. Changes in erythrocyte water or blood pH did not account for the shift of erythrocyte cations during dialysis. With recurrent dialysis changes in erythrocyte cations reflected the cumulative effect of individual dialysis and were towards a normal erythrocyte electrolyte composition. Erythrocyte magnesium resisted depletion despite low serum levels. Low dialysate magnesium levels (0.3–0.5 mg/100 ml) are required to maintain near normal serum and cellular magnesium concentrations.

Total body, Erythrocyte and Serum potassium changes during haemodialysis were studied on 29 occasions in 15 patients on maintenance dialysis with a low dialysate potassium concentration (1 mEq/l). The loss in total body potassium during haemodialysis (measured with a whole body counter) varied widely and was significantly related to the pre-dialysis body potassium state of the patient as assessed by total body potassium per kg body weight in spite of a constant high serum to dialysate concentration gradient in all patients. Serum potassium levels did not correlate well with changes in total body potassium or erythrocyte potassium. Erythrocyte potassium was shown to be a reliable and useful index of the direction and magnitude of changes in total body potassium during haemodialysis.

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