The membrane lipid composition of human brain has been studied in 21 men and 18 women 60-97 years of age. This brain tissue series is unique, because it has been obtained only from individuals who lived a normal social life in their own homes and died suddenly and unexpectedly from arteriosclerotic heart disease or ruptured aortic aneurysms. They had no history of neurological or psychiatric disease. Macroscopic and microscopic examinations ruled out any signs of organic brain disorder. The percentage of solids diminished continuously during the whole period, but the marked individual differences suggested large variations in the hydration of the brain. The content of membrane lipids also diminished continuously up to 90 years of age, when a marked diminution in level of gangliosides and cerebrosides occurred, a result indicating a rapid reduction in amount of neuronal membranes and myelin. The clinical implications of the variation in brain hydration and the rapid loss of membrane lipids after 90 years of age are discussed.

In the renal tubules of the dog sulfate and thiosulfate are reabsorbed, and thiosulfate is secreted. Secretion of thiosulfate is maximally inhibited by carinamide at plasma levels as low as 20 µg/ml; sulfate transport is not affected. Sulfate and thiosulfate mutually inhibit each other's reabsorption. Simultaneous measurement of sulfate and thiosulfate reabsorption at varying concentration ratios of the two ions indicates that this mutual inhibition is of ‘competitive’ type. At normal sulfate levels, thiosulfate reabsorption increases in a semilogarithmic fashion with rising thiosulfate levels. By using a Lineweaver-Burk plot, thiosulfate Tm (transfer maximum) was estimated at 0.65 of sulfate Tm. Assuming this ratio to be identical with the ratio between the equilibrium constants for S2O3-carrier and SO4-carrier, theoretical reabsorption rates were calculated for thiosulfate and sulfate in each other's presence. The urinary excretion of thiosulfate at low plasma levels indicates that the site of tubular secretion is not distal to the site of reabsorption. Thiosulfate secretion is inhibited by sulfate. A common carrier is suggested for reabsorption of sulfate and thiosulfate and secretion of thiosulfate.

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