Glycine betaine and proline betaine in human blood and urine

Abstract

In healthy human subjects, glycine betaine concentrations in the blood plasma are normally between 20 and 60 μmol/l, adult males tending to have higher concentrations than females. Proline betaine concentrations are more variable, ranging from undetectable to about 50 μmol/l. Both betaines are present urine. Whereas the urinary excretion of proline betaine relects plasma concentrations, with high clearance rates, there is no correlation between plasma and urine glycine betaine concentrations. The apparent clearance rates are low (usually less than 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 circulation and urine. These data suggest that glycine betaine, but not proline betaine, is important in human and other mammalian biochemistry.