B. Assel et al., GLUCOSE-METABOLISM DURING FASTING THROUGH HUMAN-PREGNANCY - COMPARISON OF TRACER METHOD WITH RESPIRATORY CALORIMETRY, The American journal of physiology, 265(3), 1993, pp. 50000351-50000356
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.