Plasma amino acid profiles at various reproductive stages in female rats

We measured the plasma levels of amino acids at various reproductive stages in femalerats, including the estrous cycle, pregnancy and lactation, and compared the resultingamino acid profiles using two- or three-dimensional figures. These figures revealed thatthe amino acid profiles of pregnant and lactating dams differed considerably from thoseduring the estrous cycle or in male rats. The plasma levels of individual amino acids werealmost the same between proestrus, estrus, metestrus and diestrus, and their profiles didnot differ significantly. However, the amino acid profiles changed during pregnancy andlactation in dams. The plasma Ser level decreased significantly in mid and late pregnancy,whereas Tyr, Gly and His decreased significantly in the late and end stages of pregnancy,and Trp and Lys significantly decreased and increased at the end of pregnancy,respectively. Much larger changes in amino acid profiles were observed during lactation,when the levels of many amino acids increased significantly, and none showed a significantdecrease. Plasma Pro, Ser and Gly levels increased continuously from day 1 until day 15 oflactation, whereas Asn and Met increased significantly from days 1 and 5 respectivelyuntil the end of lactation. These results suggest that the profiles of plasma amino acidsshow characteristic changes according to reproductive stage and that it may be necessaryto consider such differences when performing amino acid-based diagnosis.