Dietary protein quality and zinc levels in growing rats

Abstract

Previous studies from our laboratory have shown that the intake of a low quality dietary protein during either a short or a long period, causes thymus atrophy of growing rats with a significant reduction in the number of cells and the mature T cell population. Moreover, thymus atrophy was associated with Zinc deficiency. The aim of this study was to determine if the intake of this diet induced a concomitant Zinc deficiency. Rats of the Wistar strain were fed from weaning and during 10 days a 6.5% maize protein diet (M10) or a 6.5% casein diet (C10). An age-matched control group was run simultaneously (C). The only dietary variable was the protein quality, being the Zinc content the same. Food intake (g/day) was similar: (M10: 6.5±1.4, C10: 6.8±1.1). Zn levels were determined by atomic absorption spectrophotometry in plasma (P), whole blood (WB), liver (L) and thymus (T) and expressed as μg/ml and μg/g wet tissue, respectively. No differences were found in WB (M10: 3.85±0.24, C10: 3.88±1.00, C: 3.67±0.34) nor L (M10: 42.50±11.30, C10: 36.30±6.70, C: 39.10±8.60). However, P levels decreased in M10 and C10 when compared to C (M10: 1.84±0.63, C10: 1.79±0.41, C: 2.43±0.37, P<0.04) while a significant increase in thymus Zn was only found in M10 compared to C10 and C (M10: 40.00±13.20, C10: 26.50±2.70, C: 27.10±3.60, p<0.01). These results show that the intake of a low quality dietary protein might alter the distribution of plasma Zinc with a concomitant uptake of Zinc by the thymus.