GLUCOSE-METABOLISM DURING FASTING THROUGH HUMAN-PREGNANCY - COMPARISON OF TRACER METHOD WITH RESPIRATORY CALORIMETRY

Glucose turnover and glucose oxidation were quantified in six normal p regnant women serially throughout pregnancy, using [U-C-13]glucose tra cer in combination with open-circuit indirect respiratory calorimetry. Five normal nonpregnant women were studied for comparison. With advan cing gestation and increase in maternal body weight, there was a propo rtionate increase in the rate of appearance (R(a)) of glucose so that R(a) expressed per kilogram body weight did not change from the first to third trimester. The tracer measured rate of glucose oxidation expr essed per kilogram body weight also did not change significantly throu ghout pregnancy. Oxygen consumption (VO2) in pregnant subjects did not differ from that in nonpregnant subjects. However, the respiratory ex change ratio (RER) increased significantly during pregnancy (0.88 +/- 0.53 3rd trimester and 0.76 +/- 0.50 nonpregnant, P < 0.01). The estim ated contribution of carbohydrate to VO2 measured by respiratory calor imetry was greater than that measured by the tracer method. This discr epancy became wider as the respiratory quotient increased in late preg nancy. These data suggest that maternal glucose metabolism adjusts thr oughout pregnancy to meet the increased demands of the conceptus. The discrepancy between tracer method and respiratory calorimetry was prob ably due to the contribution of (fetal) lipogenesis and (maternal) glu coneogenesis to RER.