Glutamine synthetase activity in rat tissues during pregnancy and lactation

The glutamine synthetase activities of liver, striated muscle, kidney, brain, stomach, adipose tissue, small intestine and skin of rats during pregnancy, lactation and post-lactation were investigated as a probe of glutamine--and thus of ammonia--metabolism under a situation of altered amino acid utilization. There were significant increases in muscle activity in mid-pregnancy and in post-lactation. A transient relative decrease was observed in muscle enzyme on day 20 of lactation, compensated by an increase in small intestine activity. The results are discussed in light of the transporting role of nitrogen between peripheral and splanchnic tissues attributed to glutamine, as well as to the detoxyfying role of the enzyme for removal of nitrogen generated by the conceptus and by catabolism of amino acids under the increasing demand for energetic fuels in the peak of lactation.