Biological effects of alkali-treated soya protein and lactalbumin in the rat and mouse

Abstract

Diets containing 20% alkali-treated soya protein and providing 1370–2630 ppm dietary lysinoalanine produced nephrocytomegaly in the pars recta of the proximal tubule in male Sprague-Dawley and Wistar rats. The frequency of abnormally large pars recta nuclei exceeded 33% in rats fed alkali-treated soya protein providing dietary lysinoalanine levels of 2080 or 2630 ppm. There were no quantitative or qualitative differences between the renal responses of Sprague-Dawley and Wistar rats fed the same diets. Swiss-Webster mice fed alkali-treated soya protein had slightly more than twice as many enlarged pars recta nuclei as did the control group, but the shift in size distribution was not significant at the 5% level. Sprague-Dawley rats developed only minimal karyomegaly on a diet of 20% alkali-treated lactalbumin, despite a dietary lysinoalanine level of 4970 ppm. Diets containing 8 or 10% untreated lactalbumin in addition to 12% alkali-treated soya protein or 10%, alkali-treated lactalbumin did not induce nephrocytomegaly or karyomegaly, despite providing dietary lysinoalanine levels of 1753 and 2490 ppm, respectively. Sprague-Dawley and Wistar rats fed 20% alkali-treated soya protein showed elevated plasma levels of glutamic-pyruvic transaminase (GPT) and blood urea nitrogen (BUN), and had a significantly lower plasma protein content than control animals after 8 or 12 wk on the diet. Sprague-Dawley rats fed 20% alkali-treated lactalbumin had elevated GPT levels, but BUN and total plasma protein were normal; replacement of half the protein content of the diet with non-nutritive cellulose caused elevation of GPT, with no change in the BUN or plasma protein values. In rats fed 20% alkali-treated soya protein, approximately 33% of the lysinoalanine ingested daily was found in the faeces and 1·2% in the urine. No lysinoalanine was detected in liver or blood but a quantity equivalent to about 0·6% of the daily intake was found in the kidneys. Higher urinary lysinoalanine excretion (2–7% of the intake) was found in animals fed alkali-treated lactalbumin.