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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 effect of eight hours water diuresis on electrolyte excretion and urinary acidification was studied in five permanent inhabitants of a hot region. The experimental design excluded the possible influences of the normal diurnal variations on electrolyte and hydrogen ion excretion. Water diuresis induced a marked increase in ammonia output and decrease in potassium excretion. A significant (p < 0.001) inverse relationship is demonstrated between the net hydrogen ion excretion and potassium output. Glomerular filtration rate, total solute, sodium, chloride, calcium, magnesium, and titratable acid excretion were not appreciably affected. The data presented demonstrate that prolonged water diuresis in permanent inhabitants of a hot region did not appreciably alter the excretion of electrolytes except for a significant fall in potassium output. Its effect on urinary acidification was similar to that previously reported during short term water diuresis.