Kinetics of folate turnover in pregnant women (second trimester) and nonpregnant controls during folic acid supplementation: Stable-isotopic labelingof plasma folate, urinary folate and folate catabolites shows subtle effects of pregnancy on turnover of folate pools

To investigate the effects of pregnancy on folate metabolism, we conducted an 84-d study in second-trimester (gestational wk 14-25) pregnant women (n = 6) and nonpregnant controls (n = 6) with stable-isotopic tracer methods. All subjects were fed a diet containing similar to 272 nmol/d (120 mug/d) f olate from food, along with supplemental folio acid that contained 15% [3 ' ,5 '-H-2(2)] folic acid ([H-2(2)]folic acid) during d 1-41 and that was un labeled during d 42-84 to yield a constant total folate intake of 1.02 or 1 .93 mu mol/d (450 or 850 mug/d). Isotopic enrichment of plasma folate, urin ary folate and the urinary folate catabolites para-aminobenzoylglutamate (p ABG) and para-acetamidobenzoylglutamate (ApABG) was determined at intervals throughout the study. The labeling of pABG and ApABG reflected that of tis sue folate pools from which the catabolites originate. After the intake of labeled folic acid was terminated on d 41, labeling of urinary folate exhib ited a biphasic exponential decline with distinct fast and slow components. In contrast, during d 42-84, the enrichment of urinary pABG and ApABG exhi bited primarily monophasic exponential decline, and plasma folate underwent little decline of labeling during this period. Pregnant women and controls did not differ in estimates of body folate pool size and most aspects of t he excretion of labeled urinary folate and catabolites, rates of decline of excretion, and areas under the curves for folate and catabolite excretion. Pregnant women, however, tended to have a slower rate of decline of pABG t han ApABG and higher enrichment at d 42 of ApABG and pABG. These data suppo rt and extend our previous findings indicating that pregnancy (gestational wk 14-26) causes subtle changes in folate metabolism but does not elicit su bstantial increases in the rate or extent of folate turnover at these moder ately high folate intakes.