AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 1 89-R96, Copyright © 1994 by American Physiological Society

ARTICLES

Glutamate metabolism in fetus and placenta of late-gestation sheep

R. R. Moores Jr, P. R. Vaughn, F. C. Battaglia, P. V. Fennessey, R. B. Wilkening and G. Meschia
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262.

Glutamate is produced by the fetal liver and taken up by the placenta. To explore the functional meaning of this exchange, the disposal rate (DR), clearance, conversion to glutamine, and decarboxylation rate of fetal plasma glutamate were studied at 129 +/- 2 days of gestation in seven fetal lambs infused via a systemic vein with L-[2,3,3,4,4-2H5]glutamate and L-[1-14C]glutamate. In two experiments, L-[1-13C]glutamate was also infused. The mean glutamate DR and clearance were 11.9 +/- 1.3 mumol.min-1.kg-1 and 200 +/- 8 ml.min-1.kg-1, respectively. The placenta extracted 88.5 +/- 0.8% of the tracer glutamate carried by the umbilical circulation and contributed to 61.3 +/- 3.2% of the glutamate DR. Most of the 14C infused as L-[1-14C]glutamate was converted to 14CO2: 37 +/- 4% by the fetus and 41 +/- 6% by the placenta. Of the labeled glutamate taken up by the placenta, 6.2 +/- 1.5% was returned to the fetus as glutamine. The glutamine-to-glutamate enrichment ratio in fetal arterial plasma was 0.066 +/- 0.008. We conclude that fetal plasma glutamate has an exceptionally high clearance because the flux of glutamate into the placenta is virtually equal to umbilical glutamate delivery rate. The main pathway of fetal plasma glutamate disposal is oxidation by placental and fetal tissues. Placental conversion of glutamate to fetal glutamine is a relatively small component of the placental metabolism of fetal glutamate.

This article has been cited by other articles:

				M. Timmerman, R.B. Wilkening, and T.R.H. Regnault Induction of Glutamate Dehydrogenase in the Ovine Fetal Liver by Dexamethasone Infusion during Late Gestation Experimental Biology and Medicine, January 1, 2003; 228(1): 100 - 105. [Abstract] [Full Text] [PDF]

				C. Teng, F. C. Battaglia, G. Meschia, M. R. Narkewicz, and R. B. Wilkening Fetal hepatic and umbilical uptakes of glucogenic substrates during a glucagon-somatostatin infusion Am J Physiol Endocrinol Metab, March 1, 2002; 282(3): E542 - E550. [Abstract] [Full Text] [PDF]

				D. Novak, F. Quiggle, C. Artime, and M. Beveridge Regulation of glutamate transport and transport proteins in a placental cell line Am J Physiol Cell Physiol, September 1, 2001; 281(3): C1014 - C1022. [Abstract] [Full Text] [PDF]

				P. J. Thureen, S. M. Anderson, and W. W. Hay Jr. Regulation of uterine and umbilical amino acid uptakes by maternal amino acid concentrations Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2000; 279(3): R849 - R859. [Abstract] [Full Text] [PDF]

				M. Timmerman, C. Teng, R. B. Wilkening, P. Fennessey, F. C. Battaglia, and G. Meschia Effect of dexamethasone on fetal hepatic glutamine-glutamate exchange Am J Physiol Endocrinol Metab, May 1, 2000; 278(5): E839 - E845. [Abstract] [Full Text] [PDF]

				F. C. Battaglia Glutamine and Glutamate Exchange between the Fetal Liver and the Placenta J. Nutr., April 1, 2000; 130(4): 974 - 974. [Abstract] [Full Text]

				P. W. Aldoretta and W. W. Hay Jr. Effect of glucose supply on ovine uteroplacental glucose metabolism Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R947 - R958. [Abstract] [Full Text] [PDF]

				J. C. Matthews, M. J. Beveridge, M. S. Malandro, J. D. Rothstein, M. Campbell-Thompson, J. W. Verlander, M. S. Kilberg, and D. A. Novak Activity and protein localization of multiple glutamate transporters in gestation day 14 vs. day 20 rat placenta Am J Physiol Cell Physiol, March 1, 1998; 274(3): C603 - C614. [Abstract] [Full Text] [PDF]

				M. Chung, C. Teng, M. Timmerman, G. Meschia, and F. C. Battaglia Production and utilization of amino acids by ovine placenta in vivo Am J Physiol Endocrinol Metab, January 1, 1998; 274(1): E13 - E22. [Abstract] [Full Text] [PDF]