Ammonia production and glutamine incorporation into glutathione in the functioning rat kidney

Abstract

Incorporation of glutamine''s .gamma.-glutamyl moiety into glutathione was studied in the isolated perfused rat kidney under 2 conditions: a resting state and during reabsorption of a filtered glycylglycine load (designed to stimulate glutathione breakdown). Glutamine uptake and ammonia production were monitored simultaneously with [14C]glutamine (.gamma.-glutamyl moiety) incorporation into glutathione. Renal glutathione content was highly dependent upon the presence of glutamine. In its absence, glutathione levels fell 40% in 30 min, indicating synthesis does not keep pace with degradation. Presenting the kidney with a glycylglycine load doubled the rate of glutathione degradation. Perfusing kidneys with physiological L-glutamine concentration (1 mM) maintained glutathione levels significantly above those in glutamine''s absence in either condition 1 or 2. Evidence that glutamine functions as the .gamma.-glutamyl donor in glutathione synthesis was established by the significant incorporation of [14C]glutamine into glutathione during condition 1 and the accelerated incorporation rate during glycylglycine loading (condition 2). Stimulating glutathione breakdown (condition 2) resulted in a significant increase in renal glutamine uptake and ammonia production apparently via the .gamma.-glutamyltransferase pathway since inhibiting this activity blocked the incremental rise in glutamine uptake during glycylglycine loading. Stimulating .gamma.-glutamyl cycle activity with a .gamma.-glutamyl acceptor (glycylglycine) accelerates .gamma.-glutamyl donor uptake (glutamine) and ammonia production via the .gamma.-glutamyltransferase pathway.