Effect of season and exercise on dermal nitrogen losses and their relation to urinary nitrogen excretion

The present study was designed to estimate dermal nitrogen losses in summer and winter under the conditions of minimal daily activities, on a diet of standard Japanese protein intake level and to determine whether the increased dermal nitrogen losses induced by hot climate or exercise were compensated for by the decrease in urinary nitrogen excretion. Six healthy male university students served as the subjects. The daily dermal nitrogen losses (mean +/- SD) were 0.22 +/- 0.07 g or 3.10 +/- 0.58 mg/kg in winter and 0.44 +/- 0.19 g or 6.35 +/- 2.46 mg/kg in summer, showing significantly higher dermal nitrogen losses in summer than in winter. On the contrary, urinary nitrogen excretion tended to be larger in winter than in summer. Thus, renal compensation seemed to exist for the seasonal changes in dermal nitrogen losses. In the summer experiment, the subjects took light exercise besides the minimal daily activities for a 2-day exercise period. The pooled mean of daily dermal nitrogen losses during the exercise period was significantly larger than that during the sedentary period, while the urinary nitrogen excretion was almost the same in the two periods. No compensatory reduction in the urinary nitrogen excretion during the exercise period was observed under the conditions of the present study.