Involvement of gamma-glutamyltransferase in amino-acid uptake by the lactating mammary gland of the rat.

1. Arteriovenous differences of amino acids across the lactating mammary gland have been measured in normal rats and in rats injected with serine--borate (an inhibitor of gamma-glutamyltransferase). 2. Comparison of the arteriovenous differences show that gamma-glutamyltransferase is involved in amino-acid uptake by the gland. 3. Reduced-glutathione content of isolated acini incubated with high concentrations of amino acids was lower than that of the controls. 4. High concentrations of amino acids had no effect on reduced-glutathione content of isolated acini when serine--borate was added to the incubation medium. 5. The findings provide evidence for the functioning of the gamma-glutamyl cycle in the lactating mammary gland in vivo.