Diurnal Variations in the Composition of Blood and Urine of Man Living in Hot Climate

Abstract

The diurnal variations in the composition of blood and urine during 24 h recumbency and the influence of 8 h of heavy physical work on the urinary excretory patterns were examined in nine young healthy subjects, permanent inhabitants of the hot region of Eilat near the Red Sea. The effects of change in posture, heat stress, light activity, aldosterone and dehydration on the midday sodium and water excretory patterns were studied on the same subjects. The diurnal rhythms exhibited during complete rest were similar to those described in temperate climate, except for an earlier excretory peak of potassium. Heavy physical work brought about the displacement of the midday peak water and sodium excretion to the evening and changed the hydrogen ion and phosphate excretory patterns. Potassium excretion was high during the working hours and decreased gradually thereafter to a minimum during the night. It was also found that in hot climate the peak midday natriuresis and the accompanying trough in hydrogen ion excretion, considered to be a constant feature of the diurnal urinary excretory patterns, are liable to changes even under the short-term influence of factors affecting sodium homeostasis. The possible role of body sodium homeostasis as a mechanism underlying the diurnal urinary excretory patterns is suggested.

The Hormonal and Non-Hormonal Control of Renal Excretion of Calcium and Magnesium

“…Most investigators have reported a diurnal variation in the urinary ex cretion of calcium and to a smaller extent magnesium, with a greater excretion of calcium occurring in the forenoon or midday and coinciding with, or slightly preceding the peak in sodium excretion [32,70,97,217,231], The mid day peak in calcium excretion is influenced by diet, and it was greatly reduced during fasting [97] or when food was given at four hourly intervals around the clock [141].…”