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Vet Res Commun DOI 10.1007/s11259-008-9167-2 ORIGINAL ARTICLE

Equine placenta expresses glutamine synthetase
Hélio C. Manso Filho & Helena E. Costa & Guoyao Wu & Kenneth H. McKeever & Malcolm Watford

Accepted: 8 August 2008 # Springer Science + Business Media B.V. 2008

Abstract In most mammalian species the developing fetus utilizes large amounts of glutamine derived both from thematernal circulation and synthesized de novo in the placenta. The present study was designed to determine the role of the placenta in glutamine synthesis in the horse. The placentae from eight Standardbred mares were sampled immediately after parturition together with additional tissues obtained at necropsy from three Standbred mares during diestrous. Glutamine synthetase protein was detectable in thenon-pregnant horn of the placenta in amounts similar to those seen in gluteus muscle, but the amount in the pregnant horn was two times greater than in the non-pregnant horn. Glutamine was the second most abundant amino acid in amniotic fluid at a concentration of 310±26 μmole/L with that of glycine being 535±48 μmole/L. The most abundant amino acids in placental tissue were glycine (3,732±194μmole/Kg), glutamate (3,500± 343 μmole/Kg) and glutamine (2,836±208 μmole/Kg). The results illustrate the importance of glutamine to the equine fetus and establish that the placenta, particularly the pregnant horn, has considerable capacity for glutamine synthesis. Keywords Amino acids . Equine . Horse . Glutamine . Glutamine synthetase . Placenta
H. C. Manso Filho : K. H. McKeever Equine ScienceCenter, Department of Animal Sciences, Rutgers University, New Brunswick, NJ 08901, USA H. C. Manso Filho : H. E. Costa Federal Rural University of Pernambuco, Pernambuco, Brazil H. E. Costa : M. Watford Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ 08901, USA G. Wu Department of Animal Sciences, Texas A & M University, College Station, TX 77843, USA M. Watford (*)Department of Nutritional Sciences, School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, Thompson Hall, New Brunswick, NJ 08901, USA e-mail: Watford@aesop.rutgers.edu

Vet Res Commun

Introduction In many species the concentration of most amino acids, particularly glutamine, is considerably higher in fetal plasma than in the maternal circulation, reflectingthe importance of amino acid supply to the growing fetus (Chung et al. 1998; Cetin 2001; Parimi et al. 2002; Kwon et al. 2003, 2004; Wu et al. 1995). It has been reported, however, that in the fetal horse only a few plasma amino acids are present at higher concentrations than in the maternal plasma but, although such measurements are limited, they do indicate that glutamine is concentrated in theequine fetus (Silver et al. 1994; Zicker et al. 1994; Pere 2003). Glutamine is the most abundant free alpha amino acid in the circulation of most mammals (Curthoys and Watford 1995; Newsholme et al. 2003) and it plays important roles in the transport of nitrogen, carbon and energy between tissues, including a large uptake across the placenta during pregnancy. In keeping with an important role forglutamine in fetal development glutamine is the most abundant free alpha amino acid in amniotic fluid in pigs (Wu et al. 1995) and rats (Gurekian and Koski 2005). Glutamine is synthesized from glutamate and ammonia through the action of glutamine synthetase (GS; ATP glutamate-ammonia ligase; EC 6.3.1.2) which is highly expressed in those tissues, liver, skeletal muscle, lungs and adipose tissue,that show net release of glutamine into the circulation and also in the brain (Curthoys and Watford 1995; Lie-Venema et al. 1998; van Straaten et al. 2006). The presence of glutamine synthetase activity has also been reported in rat placenta (Remesar et al. 1980) and this has been confirmed in other species, including humans (DeMarco et al. 1997) and pigs (Self et al. 2004 ), where the activity...