NOTES
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by STANFORD UNIV. on 11/19/14 For personal use only.
Re-incorporationof Carbon Atoms into Plasma Glucose in Newborn Dogs SUSANE. W.HALLAND S . HETENYI JR. Department of'Plzysiology, Uni~vrsityyf'Ottawu, Ottawa, Ontcrrio K I N 9A9 Received May 8, 1975
HALL, S. E. H.. and H E T ~ N YG., I , JR. 11975. Re-incorporation of carbon atoms into plasma glucose in newborn dogs. Can. J. Physioi. Pharmacol. 53,967-968. The ratio of the total tu~noverrate ofglucose calculated with [2J Pi]glucose as the tracer and the irreversible disposal rate of glucose, calculated with [U-14C]glucoseas the tracer was found to be 1.35 t 0.28 SD ( t 0 . 0 8 SEM) in dogs 1-33 days of age. This value was unrelated to age and to the level of glucose in the plasma. Accordingly, under basal conditions the overall re-incorporation of carbon atoms into newly released glucose in pups is nearly identical with that found in grown dogs. HALL, S. E. H. et HETENYI, G., JR. 1975. Re-incorporation caf carbon atoms into plasma glucose in newborn dogs. Can. J. Physiol. Pharmacol. 53,967-968. Le rapport entre la vitesse de renouvellement totale du glucose, calculee au moyen d'[2-3H)glucose comme marqueur, et la vitesse d'utilisation irreversible du glucose, calculee avec le marqueur[U-14C]glucose, est evaluee B 1.35 + 0.28 SB (k0.08 SEM) chezdes chiens i g i s de 1-33 jours. Cette valeur est sans rapport avec 1'5ge et avec le taux de glucose plasmatique. Par condquent, dans les conditions basales, la reincorporaticbn totale des atomes de carbone dans le glucose neoformC est wnsiblement la mime chez les chiots et chez les chiens adultes. [Traduit par le journal]
In dogs (Issekutz et al. 1972), rats (Wetenyi and Mak 1972; Katz et ul. 19741, rabbits (Katz et al. 1974), and men (Van Hoof et al. 1972) the steady state turnover of glucose calculated by [2-WHlucose as tracer has been found to be considerably higher than the one calculated using [U-14Clglucose or [I -I4C]glucose. In dogs the ratio of the calculated apparent turnover rates amounted to 1.3- 1.35 (Issekutz et al. 1972). The difference has been attributed to the re-incorporation of the 14C-label into newly formed glucose via the Cori-cycle and other pathways. Tritium, attached to the second carbon atom of glucose, is not re-incorporated into newly synthesized glucose to bc released by the liver, since in the isomerization between glucose-6-P and fructose-6-P the label becomes detached and converted to water (Katz eb al. 1972) . Hence the turnover rate calculated with [Z-WHlucose as the tracer very closely approximates thc total rate of glucose released by the liver, irrespectivcly whether the glucose arises from glycogen, gluconeogenesis, or "futile" cycling, i.e. a process by which glucose is recycled and ATP consurried with no net flux of metabolites (e.g., by the simultaneous operation of hepatic glucokinase ( E C 2.7.1 -2) and glucose-6-phosphatase ( E C 3.1 .-
3.9) ). The turnover rate calculated with [U14C]glucose as tracer is actually a measure of the 'irreversible' disposal rate of glucose (Shipley et 01. 1967). The purpose of the experiments to be reported was to determine in the newborn dog the ratio of the total turnover rate of glucose as calculated using [2-3Hlglucose as tracer and the irreversible disposal rate of glucose, calculated by using [U-lT]glucose as the tracer. The re-incorporation of glucose-carbon from 3-carbon units by cyclical pathways does not result in a net gain of glucosc-carbon for the animal. However, the inability to recycle glucose-carbon rapidly and extensively would result in a diminished availability of C-atoms for incorporation into circulating glucose in pups. It is of interest therefore to establish whether recycled carbon contributes 60 the same extent to circulating glucose in pups as in adults. Moreover, such data on newborn pups could be utilized in building more comprehensive models of the glucoreg~alatsry system in the newborn animal. Steady state apparent turnover rates of glucose were calculated by the simultaneous application of 12-WH]glucosc and [U-14C]glucose in 13 pups 1-33 days of age. The pups were
CAN. J . PHYSYOL. PHARMACOL. VOL. 53, 1975
TABLE1.
Turnover rates of glucose in pups calculated with [2-3H]glucose and [U-14C]glucoseas the tracer. Mean values SD are shown
+
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by STANFORD UNIV. on 11/19/14 For personal use only.
Turnover rate, mg-kg- l -min- l Age (days) 0-2 3-8 22-33 All pups
No. of pups
Plasma glucose, mgl100 ml
5 5 3
48-t 20 126f 29 128 22
[2-3H]glucose [U-14C]glucose
+
13
anesthetized with an intraperitoneal injection of Nembutal. In seven pups, 25-30 &i each of the two tracers were injected simultaneously into the carotid artery, and blood samples were collected over the next 120 min via the same cannula. In six pups the tracers were infused into the jugular vein ( [2-3H jglucose, 0.11 ,&i/min and [U-"CC]glucose, 0.10 ,Xi/ min) over 1 h, following their simultaneous injection of 2.5 ,Xi and 2 ,Li, respectively. Rates were calculated from the steady levels of the specific activity of plasma glucose between 40 and 60 min. Details of the methodology have been published (Varma et al. 1973). Apparent turnover rates were calculated by the Stewart-Hamilton principle in the first series, and as the ratio of the rate of the tracer infusion ovcr the mean specific activity of plasma glucose in the second. The two methods have proven to be equivalent (Norwich and Hetenyi 1 97 1 ) and, as expected, gave similar results, therefore, they are presented on a single table (Table 1 ) . Plasina glucose has beell determined with a Beckman glucoseanalyzer and was isolated and counted as the penta-acetate (Jones 1965) . As shown on the table the ratio of the total glucose turnover rate and the irreversible disposal rate was found to be 1.35 with a standard deviation of k0.28 and a standard error of the mean of tO.08. This ratio does not vary significantly with age or with the plasma glucose level in pups. The ratio of 1.34 found by Issekutz et al. (1972) in grown dogs is within the confidence limits of the mean ratio in all age groups. Therefore, in spite of the age-
7 . 6 5 0.8 S.321.9 7.42 1.2
6.2k0.1 6.322.4 5.1k0.8
Ratio of tur nover rates 1.22k0.11 1.41 k 0 . 4 1 1.46k0.19 1 . 3 5 2 0.28
related differences in plasma glucose levels, the overall rate of the re-incorporation of carbon atoms into circulating glucose by recirculation via 3-carbon atom fragments and by futile cycles was not found to be dependent on age. The authors thank Mrs. lleana Popescu and Mrs. Isabel Barnes for their skillful and devoted assistance, and Mrs. Marie Gagni for secretarial help. The study was supported by a generous grant from the Medical Research Council of Canada.
HETENYI,G., JR., and PVIAK, D. 1970. 3H-2-glucose as tracer in turnover studies. Can. J. Physiol. Pharmacol. 48.732-734. ISSEKUTZ, B., JR., ALIEN, M . , and BORKOW,I. 1972. Estimation of the glucose turnover in the dog with Am. C . J. Physiol. 222, glucose-2-T and g l ~ c o s e - U - ~ ~ 710-712. JONES,G. B. 1965. Determination of the specific activity of labelled blood glucose by liquid scintillation using glucose pentaacetate. Anal. Biochem. 12,249-253. KATZ,J., DUNN,A., CHENOWETH, M . , and GOLDEN, S. 1974. Determination of synthesis, body mass of glucose in rats and rabbits in vivo with ? H and I4C-labelledglucose. Biochern. J. 142, 171-183. NORWICH, K. H., and HETENYI,G., JR. 1971. Basic studies on metabolic steady states. Bull. Math. Biophys. 33,403-412. SHIPLEY,R. A., CHUDZIK,E. B., GIBBONS,A. P.. JONGEDYK, K., and BRUMMOND, D. 0. 1967. Rate of glucose transformation in the rat by whole body C . J. Physiol. 213, analysis after g l u ~ o s e - ~ ~Am. 1149-1 158. VAN HOOF, F., HUE, L., BARSY,T., JACQUEMIN, P., Devos, P., and HERS,PI. G. 1972. Glycogen storage diseases. Biochimie, 54,745-751. S., RAKUSAN, K., COWAN,J. S., and HETENYI, VARMA, G., JR. 1973. Stimulation of glucose production by hypoxia in newborn dogs. Can. J . Physiol. Pharrnacol. 51,464-471.
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by STANFORD UNIV. on 11/19/14 For personal use only.
Re-incorporationof Carbon Atoms into Plasma Glucose in Newborn Dogs SUSANE. W.HALLAND S . HETENYI JR. Department of'Plzysiology, Uni~vrsityyf'Ottawu, Ottawa, Ontcrrio K I N 9A9 Received May 8, 1975
HALL, S. E. H.. and H E T ~ N YG., I , JR. 11975. Re-incorporation of carbon atoms into plasma glucose in newborn dogs. Can. J. Physioi. Pharmacol. 53,967-968. The ratio of the total tu~noverrate ofglucose calculated with [2J Pi]glucose as the tracer and the irreversible disposal rate of glucose, calculated with [U-14C]glucoseas the tracer was found to be 1.35 t 0.28 SD ( t 0 . 0 8 SEM) in dogs 1-33 days of age. This value was unrelated to age and to the level of glucose in the plasma. Accordingly, under basal conditions the overall re-incorporation of carbon atoms into newly released glucose in pups is nearly identical with that found in grown dogs. HALL, S. E. H. et HETENYI, G., JR. 1975. Re-incorporation caf carbon atoms into plasma glucose in newborn dogs. Can. J. Physiol. Pharmacol. 53,967-968. Le rapport entre la vitesse de renouvellement totale du glucose, calculee au moyen d'[2-3H)glucose comme marqueur, et la vitesse d'utilisation irreversible du glucose, calculee avec le marqueur[U-14C]glucose, est evaluee B 1.35 + 0.28 SB (k0.08 SEM) chezdes chiens i g i s de 1-33 jours. Cette valeur est sans rapport avec 1'5ge et avec le taux de glucose plasmatique. Par condquent, dans les conditions basales, la reincorporaticbn totale des atomes de carbone dans le glucose neoformC est wnsiblement la mime chez les chiots et chez les chiens adultes. [Traduit par le journal]
In dogs (Issekutz et al. 1972), rats (Wetenyi and Mak 1972; Katz et ul. 19741, rabbits (Katz et al. 1974), and men (Van Hoof et al. 1972) the steady state turnover of glucose calculated by [2-WHlucose as tracer has been found to be considerably higher than the one calculated using [U-14Clglucose or [I -I4C]glucose. In dogs the ratio of the calculated apparent turnover rates amounted to 1.3- 1.35 (Issekutz et al. 1972). The difference has been attributed to the re-incorporation of the 14C-label into newly formed glucose via the Cori-cycle and other pathways. Tritium, attached to the second carbon atom of glucose, is not re-incorporated into newly synthesized glucose to bc released by the liver, since in the isomerization between glucose-6-P and fructose-6-P the label becomes detached and converted to water (Katz eb al. 1972) . Hence the turnover rate calculated with [Z-WHlucose as the tracer very closely approximates thc total rate of glucose released by the liver, irrespectivcly whether the glucose arises from glycogen, gluconeogenesis, or "futile" cycling, i.e. a process by which glucose is recycled and ATP consurried with no net flux of metabolites (e.g., by the simultaneous operation of hepatic glucokinase ( E C 2.7.1 -2) and glucose-6-phosphatase ( E C 3.1 .-
3.9) ). The turnover rate calculated with [U14C]glucose as tracer is actually a measure of the 'irreversible' disposal rate of glucose (Shipley et 01. 1967). The purpose of the experiments to be reported was to determine in the newborn dog the ratio of the total turnover rate of glucose as calculated using [2-3Hlglucose as tracer and the irreversible disposal rate of glucose, calculated by using [U-lT]glucose as the tracer. The re-incorporation of glucose-carbon from 3-carbon units by cyclical pathways does not result in a net gain of glucosc-carbon for the animal. However, the inability to recycle glucose-carbon rapidly and extensively would result in a diminished availability of C-atoms for incorporation into circulating glucose in pups. It is of interest therefore to establish whether recycled carbon contributes 60 the same extent to circulating glucose in pups as in adults. Moreover, such data on newborn pups could be utilized in building more comprehensive models of the glucoreg~alatsry system in the newborn animal. Steady state apparent turnover rates of glucose were calculated by the simultaneous application of 12-WH]glucosc and [U-14C]glucose in 13 pups 1-33 days of age. The pups were
CAN. J . PHYSYOL. PHARMACOL. VOL. 53, 1975
TABLE1.
Turnover rates of glucose in pups calculated with [2-3H]glucose and [U-14C]glucoseas the tracer. Mean values SD are shown
+
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by STANFORD UNIV. on 11/19/14 For personal use only.
Turnover rate, mg-kg- l -min- l Age (days) 0-2 3-8 22-33 All pups
No. of pups
Plasma glucose, mgl100 ml
5 5 3
48-t 20 126f 29 128 22
[2-3H]glucose [U-14C]glucose
+
13
anesthetized with an intraperitoneal injection of Nembutal. In seven pups, 25-30 &i each of the two tracers were injected simultaneously into the carotid artery, and blood samples were collected over the next 120 min via the same cannula. In six pups the tracers were infused into the jugular vein ( [2-3H jglucose, 0.11 ,&i/min and [U-"CC]glucose, 0.10 ,Xi/ min) over 1 h, following their simultaneous injection of 2.5 ,Xi and 2 ,Li, respectively. Rates were calculated from the steady levels of the specific activity of plasma glucose between 40 and 60 min. Details of the methodology have been published (Varma et al. 1973). Apparent turnover rates were calculated by the Stewart-Hamilton principle in the first series, and as the ratio of the rate of the tracer infusion ovcr the mean specific activity of plasma glucose in the second. The two methods have proven to be equivalent (Norwich and Hetenyi 1 97 1 ) and, as expected, gave similar results, therefore, they are presented on a single table (Table 1 ) . Plasina glucose has beell determined with a Beckman glucoseanalyzer and was isolated and counted as the penta-acetate (Jones 1965) . As shown on the table the ratio of the total glucose turnover rate and the irreversible disposal rate was found to be 1.35 with a standard deviation of k0.28 and a standard error of the mean of tO.08. This ratio does not vary significantly with age or with the plasma glucose level in pups. The ratio of 1.34 found by Issekutz et al. (1972) in grown dogs is within the confidence limits of the mean ratio in all age groups. Therefore, in spite of the age-
7 . 6 5 0.8 S.321.9 7.42 1.2
6.2k0.1 6.322.4 5.1k0.8
Ratio of tur nover rates 1.22k0.11 1.41 k 0 . 4 1 1.46k0.19 1 . 3 5 2 0.28
related differences in plasma glucose levels, the overall rate of the re-incorporation of carbon atoms into circulating glucose by recirculation via 3-carbon atom fragments and by futile cycles was not found to be dependent on age. The authors thank Mrs. lleana Popescu and Mrs. Isabel Barnes for their skillful and devoted assistance, and Mrs. Marie Gagni for secretarial help. The study was supported by a generous grant from the Medical Research Council of Canada.
HETENYI,G., JR., and PVIAK, D. 1970. 3H-2-glucose as tracer in turnover studies. Can. J. Physiol. Pharmacol. 48.732-734. ISSEKUTZ, B., JR., ALIEN, M . , and BORKOW,I. 1972. Estimation of the glucose turnover in the dog with Am. C . J. Physiol. 222, glucose-2-T and g l ~ c o s e - U - ~ ~ 710-712. JONES,G. B. 1965. Determination of the specific activity of labelled blood glucose by liquid scintillation using glucose pentaacetate. Anal. Biochem. 12,249-253. KATZ,J., DUNN,A., CHENOWETH, M . , and GOLDEN, S. 1974. Determination of synthesis, body mass of glucose in rats and rabbits in vivo with ? H and I4C-labelledglucose. Biochern. J. 142, 171-183. NORWICH, K. H., and HETENYI,G., JR. 1971. Basic studies on metabolic steady states. Bull. Math. Biophys. 33,403-412. SHIPLEY,R. A., CHUDZIK,E. B., GIBBONS,A. P.. JONGEDYK, K., and BRUMMOND, D. 0. 1967. Rate of glucose transformation in the rat by whole body C . J. Physiol. 213, analysis after g l u ~ o s e - ~ ~Am. 1149-1 158. VAN HOOF, F., HUE, L., BARSY,T., JACQUEMIN, P., Devos, P., and HERS,PI. G. 1972. Glycogen storage diseases. Biochimie, 54,745-751. S., RAKUSAN, K., COWAN,J. S., and HETENYI, VARMA, G., JR. 1973. Stimulation of glucose production by hypoxia in newborn dogs. Can. J . Physiol. Pharrnacol. 51,464-471.
