Enzyme activities in the sheep placenta during the last three months of pregnancy

Edwards, Elizabeth M.; Rattenbury, J M; Varnam, G.Carole E.; Dhand, Usha K.; Jeacock, Marjorie K.; Shepherd, David

doi:10.1016/0304-4165(77)90146-5

Cited by 32 publications

(13 citation statements)

References 24 publications

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“…The levels of activity found are higher than those of developing sheep placentae and lower than those of full-term human and sheep placentae [2,7]. The distinctly higher activity found here at 19 days is not found in the sheep at comparable developing stages.…”

Section: Discussioncontrasting

confidence: 67%

“…The alanine and aspartate transaminase activities have been determined in a number of points during the intra-uterine development of sheep [2], humans at term [5] and rats in different stages of development [1,4]; in spite of the data not being directly comparable, because of the use by these authors of highspeed supernatants for the determination of enzyme activities, the data fall in the same general range as ours. However, the developing patterns found in the literature for alanine and aspartate transaminases [l] in rat placenta do not coincide totally with ours, as the data presented here do not show significant differenccs (per unit of protein weight) between all three groups studied, in contrast with a significant decrease observed by these authors in both enzymes [I]; these differences can be partly due to methodological variations in the process of separation of the enzyme source.…”

Section: Discussionmentioning

confidence: 57%

“…The arginase activity of sheep and human placentae has been also measured [2,7]. The levels of activity found are higher than those of developing sheep placentae and lower than those of full-term human and sheep placentae [2,7].…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the enzyme activities found in placenta are considerable, and explain an active glucidic and intermediary metabolism [l, 21; however, the amino acid metabolism of the placenta has been only sparsely studied, mainly in relation to transaminases [I -51 ; but also adenylate deaminase [6] and arginase [2,7] have been isolated and/or studied. Human placental gluconeogenic amino acid oxidation has been also described [8].…”

mentioning

confidence: 99%

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Activities of Enzymes Involved in Amino‐Acid Metabolism in Developing Rat Placenta

Remesar

Arola

Palou

et al. 1980

European Journal of Biochemistry

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Aspartate transaminase, alanine transaminase, glutamate dehydrogenase, arginase, serine dehydratase, tyrosine transaminase, glutamine synthetase, glutaminase and adenylate deaminase activities were measured in crude homogenates of 12, 19 and 21-day rat placentae. There is a considerable quantitative importance in enzymes able to produce free ammonia, such as adenylate deaminase and glutamate dehydrogenase, activity that progressively decrease with the age of placenta. The glutamine synthetase and tyrosine transaminase activities increase with age, while serine dehydratase decreases considerably and aspartate and alanine transaminase do not change practically. Arginase shows a maximum at 19, with lower 12 and 21-day activities. No measurable glutaminase activity has been found.The possible implications of the enzymes studied upon the ammonia-producing activity of rat placenta are discussed together with the relative decreasing role of placenta for the overall metabolic activity of the foetus, especially during the last phases of its development.The placenta is the interface through which the embryo first, and then the foetus, receive. the foodstuffs needed for their development at the expense of the maternal organism. The vital cycle of the placenta is related to its size relative to that of the foetus; it initially carries on many metabolic functions that are later taken up by other foetal organs, ending its physiological use with birth, when it is totally discarded.The metabolic functions of the placenta are manifold in addition to its main connecting and transporting role. Thus, the enzyme activities found in placenta are considerable, and explain an active glucidic and intermediary metabolism [l, 21; however, the amino acid metabolism of the placenta has been only sparsely studied, mainly in relation to transaminases [I -51 ; but also adenylate deaminase [6] and arginase [2,7] have been isolated and/or studied. Human placental gluconeogenic amino acid oxidation has been also described [8].

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Section: Discussioncontrasting

confidence: 67%

Section: Discussionmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Activities of Enzymes Involved in Amino‐Acid Metabolism in Developing Rat Placenta

Remesar

Arola

Palou

et al. 1980

European Journal of Biochemistry

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“…This could occur by catabolism of arginine to ornithine and urea in the placenta via arginase action. Arginase reaches maximal concentrations in the sheep placenta in late gestation (25). Whether its concentration or activity could be augmented by increased arginine uptake by the placenta is not known.…”

mentioning

confidence: 99%

Ovine Placental and Fetal Arginine Metabolism at Normal and Increased Maternal Plasma Arginine Concentrations

et al. 2002

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Arginine (A) may play a significant role in fetal growth, by stimulating insulin secretion and as a precursor for both polyamine synthesis and nitric oxide production. To determine whether increased maternal plasma A concentrations can enhance delivery of A to the fetus, uterine, umbilical, and net uteroplacental (UP) A uptake rates were measured in 12 pregnant ewes at 129.6 Ϯ 0.4 d gestation (mean Ϯ SEM) during normal and after 3 h of increased maternal plasma A concentrations. With a 2.7-fold increase in maternal plasma A concentrations (p Ͻ 0.001), there were significant increases in uterine A uptake (13.8 Ϯ 1.0 to 41.3 Ϯ 7.7 mol/min, p Ͻ 0.005), umbilical A uptake (3.3 Ϯ 0.5 to 5.2 Ϯ 0.8 mol·min Ϫ1 ·kg Ϫ1 fetus, p Ͻ 0.005), UP A uptake (17.8 Ϯ 6.2 to 89.2 Ϯ 20.3 mol·min Ϫ1 ·kg Ϫ1 placenta, p Ͻ 0.01), fetal arterial A concentration (98.7 Ϯ 6.3 to 137.1 Ϯ 9.9 M, p Ͻ 0.001), maternal A disposal rate (143.7 Ϯ 9.4 to 217.0 Ϯ 6.7 mol/min, p Ͻ 0.001), fetal A disposal rate (7.9 Ϯ 0.8 to 9.9 Ϯ 1.1 mol·min Ϫ1 ·kg Ϫ1 , p Ͻ 0.05), fetal A oxidation rate (1.31 Ϯ 0.24 to 1.84 Ϯ 0.36 mol·min Ϫ1 ·kg Ϫ1 , p Ͻ 0.05), and plasma insulin concentration in both fetus (16 Ϯ 2 to 20 Ϯ 2 U/mL, p Ͻ 0.001) and mother (24 Ϯ 3 to 32 Ϯ 4 U/mL, p Ͻ 0.001). Thus, increased maternal plasma A concentration increases maternal, UP, and fetal A net uptake, and increases insulin secretion in mother and fetus. The 4.2-fold larger increase in UP than net fetal A uptake could represent preferential UP A metabolism relative to fetal A metabolism, relatively limited placental-fetal A transport capacity compared with uterine A uptake capacity, or both; responsible mechanisms remain unknown. Arginine is a conditionally indispensable amino acid in the mammalian fetus and neonate (1, 2), and maintenance of fetal arginine supply and plasma concentrations are important for optimal fetal growth. The mechanisms by which arginine promotes fetal growth, however, are multifaceted and have not been adequately investigated. Arginine is an insulin secretagogue in ovine and human fetuses (3-7) and in human newborns (8 -10); thus the role of arginine in fetal growth may include an insulin-mediated anabolic effect. In addition, arginine could stimulate growth as a precursor for polyamine synthesis (11) and nitric oxide production (12-14).In contrast, arginine deficiency has been shown to induce growth restriction in experimental animals (15, 16). A potential therapy for fetal growth restriction, therefore, could include maternal plasma arginine supplementation in an attempt to increase fetal arginine supply. It is not known, however, whether increasing maternal plasma arginine concentration could increase net fetal arginine uptake, fetal plasma arginine concentration, or fetal insulin concentration. In addition, the characteristics of placental arginine uptake, metabolism, and transport to the fetus have not been determined. Therefore, this study was designed to determine how maternal arginine supplementation affects maternal, uteroplacental, and fetal arginine net ...

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Nitric Oxide Dysfunction in the Pathophysiology of Preeclampsia

Lowe¹

2000

Nitric Oxide

146

106

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Enzyme activities in the sheep placenta during the last three months of pregnancy

Cited by 32 publications

References 24 publications

Activities of Enzymes Involved in Amino‐Acid Metabolism in Developing Rat Placenta

Activities of Enzymes Involved in Amino‐Acid Metabolism in Developing Rat Placenta

Ovine Placental and Fetal Arginine Metabolism at Normal and Increased Maternal Plasma Arginine Concentrations

Nitric Oxide Dysfunction in the Pathophysiology of Preeclampsia

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