SummaryThe purpose of this study was to clarify the effects of nutrients on the gonadal development of male rats kept under constant darkness as a model of disturbed daily rhythm. The present study examined protein and vitamins, and their interactions. This study was based on three-way ANOVA; the three factors were lighting conditions, dietary protein and dietary vitamins, respectively. The levels of dietary protein were low or normal: 9% casein or 20% casein. The levels of dietary vitamins were low, normal or high: 1/3.3 of normal (AIN-93G diet) content, normal content, or three times the normal content, respectively. Other compositions were the same as those of the AIN-93G diet, and six kinds of experimental diet were prepared. Four-week-old rats (Fischer 344 strain) were kept under constant darkness or normal lighting (12-h light/dark cycle) for 4 wk. After 4 wk, the gonadal weights and serum testosterone content were evaluated. In the constant darkness groups (D-groups), the low-protein diet induced reduction of gonadal organ weights and serum testosterone concentrations. This reduction of gonadal organ weights was exacerbated by progressively higher levels of dietary vitamins. In the case of a normal-protein diet, the depression of gonadal development was not accelerated by high-vitamin intake. In the normal lighting groups (N-groups), the low-protein and high-vitamin diet slightly depressed gonadal development. These results suggest that the metabolism of protein and vitamins is different in rats being kept under constant darkness, and that excess dietary vitamins have an adverse effect on gonadal development in rats fed a low-protein diet.
230The number of people living under disturbed daily rhythm has been increasing due to the globalization of business and social activities as well as the diversifi cation of the forms of labor. Such irregularities in daily rhythm adversely affect bio-regulatory mechanisms, resulting in an abnormal diurnal rhythm that can impede biological activities structurally and functionally. However, there is currently no source of collected basic data on the nutritional aspects of maintaining or promoting health under the condition of disturbed daily rhythm. The perspective behind this research is as follows: as basic data on the relationship between nutritional status and gonadal development in rats with disturbed daily rhythm accumulate, these data can be used for human research, and fi nally, dietary reference intakes can be compiled for persons living under disturbed daily rhythm.Lighting is one of the key external factors for the formation of daily rhythm. Rats kept under constant darkness develop disturbances in their feeding and motoractivity rhythms, and suffer from altered rhythms of hormone secretion and enzyme activity (1, 2). Esashi et al. (3,4) have reported that rats kept under constant darkness showed depressed gonadal development and a decreased delivery rate. The depression of gonadal development in these rats was accelerated by a low-protein diet (4). These fi ndings indicate that the gonads have high sensitivity to constant darkness and nutrients.In previous papers, we have reported the effects on rat gonadal development of protein, methionine, vitamins, minerals and oil (5), minerals (6), amino acids, an AIN-76 diet and an AIN-93G diet (7), the interaction between protein and vitamins (8), water-and fat-soluble vitamins (9) and each of the fat-soluble vitamins (10). We have demonstrated that a high level (three times the normal (AIN-93G)) of water-soluble vitamin and a low level (1/3.3 of normal) of fat-soluble vitamin diet mitigated the depression of gonadal development in rats kept under constant darkness (9). Therefore, as a next step, we attempted to clarify the effects on gonadal development of nine kinds of water-soluble vitamins under a diet with a low level of fat-soluble vitamins. In this experiment, the content of each water-soluble vitamin was normal or six times the normal content. This study was divided into two experiments, because a single experiment to test all nine water-soluble vitamins couldn't be done. In the fi rst experiment (Ex. 1) we examined seven water-soluble vitamins, and in the second experiment (Ex. 2) we examined two water-soluble vitamins. Experiment 1 was carried out using an orthogonal array (11, 12), which is the experimental design we applied in previous studies (5-7, 10), and Ex. Summary The purpose of this study was to clarify the effects of nutrients on the gonadal development of male rats kept under constant darkness as a model of disturbed daily rhythm. In the present study we examined the effects of nine water-soluble vitamins. We selected 7 water-soluble vitam...
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