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The effect of 5 days of sleep deprivation on the circadian rhythm of serum iron was studied in a group of six healthy male volunteers. The results were compared with a control group of five individuals, whose normal sleep cycle was preserved, but whose daily regimen was otherwise identical with the sleep deprivation group. Their biorhythm was processed mathematically using cosinor analysis. Sleep deprivation markedly reduced the mean level of iron, diminished the absolute and relative amplitude of oscillations, disturbed the shape of the daily course of serum iron and gradually decreased the computative acrophase, i.e., shortened the period of rhythm. Forty-eight hours of recovery resulted only in a partial normalization of all the observed changes. The potential mechanisms of the observed changes are discussed.

The effect of 120-h sleep deprivation on the activity of selected enzymes of energy metabolism in skeletal muscle was studied in seven healthy volunteers. The results showed a significant decrease in the activity of malate dehydrogenase, citrate synthase, glycerol-3-phosphate dehydrogenase and lactate dehydrogenase. Triosephosphate dehydrogenase, hexokinase, and hydroxyacyl-CoA-dehydrogenase activities showed an insignificant decrease. The findings are indicative of (1) decreased aerobic oxidation capacity; (2) reduced function of reducing-equivalent carriers from cytosol across the mitochondrial membrane; (3) relative accentuation of the non-aerobic glycolytic pathway; (4) a prediabetic type of muscle metabolism.

Prolonged sleep deprivation elicits a significant elevation of the plasma level of free tryptophan which appears to be involved in increased excretion of 5-HIAA during this state through enhanced 5-HT synthesis.