Urinary Free Amino Acid Excretions During Successive Pregnancies

Abstract

Investigators( 1-9) have shown that there is little correlation between the quality or quantity of protein ingested and the amounts of amino acids excreted. Wallraff (lo) reported that the free, rather than the total amino acids are excreted in significantly higher amounts during pregnancy. A study in this laboratory of 15 women during the reproductive cycle( 11) disclosed that the excretion of specific free amino acids may be used as an index of physiological adaptation of the maternal body to the growth and development of the products of conception. In the investigation reported here, 24-hour collections of urine from one woman during 3 successive reproductive cycles were analyzed for free threonine, histidine, lysine, tryptophan, phenylalanine, isoleucine, valine, leucine, arginine, and met hionine .The subject of study is a white American woman 5 feet, 7 inches tall and weighing approximately 150 lb, who was studied while she was 23 to 25 years old. Her blood type is B, Rh negative. Before pregnancy she had a basal metabolic rate of -23 and between the second and third pregnancies, the rate was + l . Frequent medical examinations before and throughout the study showed her to be in good physical health. For the subject, ranges of weight, blood pressure, hemoglobin, red and white blood counts during the 30-month study period are given in Table I. Estimated length of gestation and the infants' birth weights also are included. Carefully-checked dietary history and food intakes recorded for each 24-hour period in which urine samples were collected indicated that the subject's dietary habits were good. Eighteen 24-hour urine samples were collected for amino acid analysis. One sample was obtained when the woman was nulligravid; 8 samples were collected at approximately monthly intervals during her first pregnancy, Experimental.the first in the second month (44 days after the last menstrual period), and a sample was procured during lactation, 47 days postpartum; 6 samples were obtained during the second reproductive cycle, one 6 months postpartum when the subject was not lactating; and during the third pregnancy, urine samples were collected in the second and fourth months. All samples were preserved with small amounts of glacial acetic acid stored at -20°C pending analysis. Microbiological methods reported previously( 12) were used in determining the 10 free amino acids. The organisms used were Lactobacillus plantarum for leucine, isoleucine, and valine ; Leuconostoc mnesenteroides for histidine, lysine, methionine, and phenylalanine ; and Streptococcus faecalis for arginine, threonine, and tryptophan. Total assay volume was 3 ml and growth responses were measured turbidimetrically. Amino acid values reported are averages of 2 or more assays in which determinations were run in duplicate at 5 levels. Duplicate assays which did not check with t S % were repeated.

Maternal-fetal metabolism in normal pregnancy and preeclampsia

“…The concentration of most amino acids in the maternal circulation decrease early in pregnancy, remain lower throughout pregnancy and increase to nonpregnant levels after delivery (115,116). The mechanism responsible for this change in maternal plasma amino acids during pregnancy is likely related to changes in renal function since amino acids are readily filtered by the glomerulus and amino acid reabsorption by the proximal tubules is decreased during pregnancy (116)(117)(118)(119). In addition, these changes in circulating amino acid concentrations are likely affected by changes in metabolism, specifically increases in protein synthesis needs (120).…”