Comparison of the effects of dietary protein on the sexual organ development of male mice and rats kept under constant darkness.

The purpose of this study was to determine whether the effects of dietary protein on sexual organ development were different in mice and rats kept under constant darkness. Four-week-old mice (ICR strain) and rats (F344 strain) were kept under constant darkness (D) or normal lighting (N; 12-h light/dark cycle) for 4 wk. The dietary protein level was 9% casein with the addition of 0.135% cystine (9PC) or without it (9P); other components of the diet were based on the AIN-93G diet. The testes and epididymides weights (g/100 g BW) of the rats given the 9P diet in the D-group were lower than those of the rats given the 9P diet in the N-group. In the mice, lighting conditions and diet did not affect testes or epididymides weights. Body weight and food intake in the rats were affected by diet, and these values were lower in the 9P diet group; however, body weight and food intake in the mice was not affected by diet. The serum albumin concentration in the rats was lower in the 9P diet group, while that of the mice was lower in the 9PC diet group. In the rats kept under constant darkness, a diet lacking in cystine accelerated the suppression of sexual organ development and decreased serum albumin concentration, but this diet had no such effects on the mice. The finding that the effects of dietary protein were different in mice and rats suggests that protein requirements of mice are different from those of rats.