Abstract
Based on studies of glutamine flux in the ovine placenta, we hypothesize that the human placenta is capable of substantial glutamine synthesis via glutamine synthetase (GS) and has little capacity to deaminate glutamine via glutaminase (GA). GS and GA activities and GS transcript were examined on freshly obtained homogenates from term human placenta and compared to values obtained from other organs known to be primarily producers or consumers of glutamine. The activity of GS and transcript size (1.8 and 2.8 kB species) in human placenta is comparable to that observed in adult rat lung, an organ known to be an important glutamine producer involved in glutamine homeostasis. GS activity in the placenta is higher than that in adult rat small intestine which is a major glutamine consumer rather than a glutamine producer. Placental GA shows low activity (0.21 ± 0.29 μmoles • mg protein-1 indicating that the human placenta converts very little glutamine to glutamate. Low activity of GA suggests that the placenta has little need to convert glutamine to glutamate. The human placenta may, like the ovine placenta, derive sufficient glutamate from the fetus for incorporation into the citric acid cycle. These results: 1) suggest that the human placenta, like the rat lung, is a glutamine producing organ; and 2) are consistent with the presence of an ovine-like glutamine-glutamate shuttle between the human placenta and fetal liver. Supported by NIH Grant#RO1-HD29279. Table
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