GLYCINE BETAINE AND PROLINE BETAINE IN HUMAN BLOOD AND URINE

In healthy human subjects, glycine betaine concentrations in the blood plasma are normally between 20 and 60 mu mol/l, adult males tending t o have higher concentrations than females. Proline betaine concentrati ons are more variable, ranging from undetectable to about 50 mu mol/l. Both betaines are present in urine. Whereas the urinary excretion of proline betaine reflects plasma concentrations, with high clearance ra tes, there is no correlation between plasma and urine glycine betaine concentrations. The apparent clearance rates are low (usually less tha n 5%). The proline betaine content of human kidney tissue is less than 0.1% of the glycine betaine content, and this is true also of rabbit tissue despite high concentrations of both betaines in rabbit circulat ion and urine. These data suggest that glycine betaine, but not prolin e betaine, is important in human and other mammalian biochemistry.