TY - JOUR
T1 - Tracer disequilibrium in CO2 compartments during NaH14CO3 infusion
AU - Hamel, N.
AU - Divertie, G.
AU - Silverberg, J.
AU - Persson, M.
AU - Miles, J.
N1 - Funding Information:
From the Endocrine Research Unit, Mayo Medical School, Rochester, MN. Submitted Mav 28, 1992; accepted August 19. 1’492. Supported in part by grants from the US Public Health Service (DK-38092 and RR-00585) and the Mayo Foundation. Address reprint requests to J. Miles. MD, Endocrine Research Umt. Mayo Clinic, Rochester, MN 55905. Copyright 0 1993 by W.B. Saunders Cornpan\ 0026O495/9.?fJ208-0012$03.00/0
PY - 1993/8
Y1 - 1993/8
N2 - The failure of labeled CO2 to equilibrate between extracellular and intracellular CO2 compartments may influence the accuracy of substrate oxidation measurements during infusion of carbon-labeled tracers because it may generate errors in estimate of fixation of labeled CO2 derived from control experiments in which labeled bicarbonate is infused. In this study, normal volunteers received a 14-hour overnight primed continuous infusion of NaH14CO3. Over the last 4 hours of the study, steady-state conditions were achieved in the specific activities (SAs) of expired 14CO2 and plasma urea, which was used as a probe for hepatic intracellular CO2 SA. Plasma urea SA was approximately 17% lower than expired CO2 SA (46.4 ± 5.6 v 56.8 ± 3.9 disintegrations per minute · μmol-1, P < .02). Fractional 14CO2 recovery was 94.8% ± 0.8%; when corrected for failure to equilibrate with intracellular CO2, fractional recovery was 89.5% ± 1.9%. These data indicate that compartmentalization of CO2 may occur in humans. The duration of our experiments, required because of the long half-life of plasma urea, may have minimized the apparent magnitude of compartmentalization. Furthermore, it is possible that compartmentalization in extrahepatic tissues could be of either lesser or greater magnitude than that which we observed in liver. Whether this phenomenon contributes to incomplete recovery of 14CO2 during NaH14CO3 infusion cannot be determined from our results. Additional studies using different experimental approaches will be required to better measure CO2 compartmentalization.
AB - The failure of labeled CO2 to equilibrate between extracellular and intracellular CO2 compartments may influence the accuracy of substrate oxidation measurements during infusion of carbon-labeled tracers because it may generate errors in estimate of fixation of labeled CO2 derived from control experiments in which labeled bicarbonate is infused. In this study, normal volunteers received a 14-hour overnight primed continuous infusion of NaH14CO3. Over the last 4 hours of the study, steady-state conditions were achieved in the specific activities (SAs) of expired 14CO2 and plasma urea, which was used as a probe for hepatic intracellular CO2 SA. Plasma urea SA was approximately 17% lower than expired CO2 SA (46.4 ± 5.6 v 56.8 ± 3.9 disintegrations per minute · μmol-1, P < .02). Fractional 14CO2 recovery was 94.8% ± 0.8%; when corrected for failure to equilibrate with intracellular CO2, fractional recovery was 89.5% ± 1.9%. These data indicate that compartmentalization of CO2 may occur in humans. The duration of our experiments, required because of the long half-life of plasma urea, may have minimized the apparent magnitude of compartmentalization. Furthermore, it is possible that compartmentalization in extrahepatic tissues could be of either lesser or greater magnitude than that which we observed in liver. Whether this phenomenon contributes to incomplete recovery of 14CO2 during NaH14CO3 infusion cannot be determined from our results. Additional studies using different experimental approaches will be required to better measure CO2 compartmentalization.
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U2 - 10.1016/0026-0495(93)90012-D
DO - 10.1016/0026-0495(93)90012-D
M3 - Article
C2 - 8393958
AN - SCOPUS:0027650468
SN - 0026-0495
VL - 42
SP - 993
EP - 997
JO - Metabolism
JF - Metabolism
IS - 8
ER -