Vettenranta K, Raivio K O
Children's Hospital, University of Helsinki, Finland.
Placenta. 1988 Jan-Feb;9(1):27-37. doi: 10.1016/0143-4004(88)90070-7.
Using density gradient centrifugation, human trophoblastic cells were enriched from mixed cell populations of enzymatically dispersed first- and third-trimester placentae. Over 95 per cent of the cells recovered were of epithelial (i.e., trophoblastic) origin, as evidenced by their cytokeratin intermediate filament positivity and vimentin negativity, examined using indirect immunofluorescence, and also by their high content of human chorionic gonadotrophin. The activities of key enzymes involved in purine degradation and re-utilization (5'-nucleotidase; AMP-deaminase; hypoxanthine phosphoribosyltransferase (HPRT); xanthine dehydrogenase/oxidase) as well as the total activity of alkaline phosphatase were measured in the trophoblastic cells. A six-fold increase in the trophoblastic alkaline phosphatase activity was noted between the first and third trimester. A 40 per cent decrease was noted in the activity of 5'-nucleotidase, which, on the basis of kinetic properties, appears to have a dominant role in the dephosphorylation of placental nucleoside-5'-monophosphates. The trophoblastic activities of AMP-deaminase, HPRT, and xanthine dehydrogenase/oxidase did not change as a function of the gestational age. In view of the relative activities of the latter two enzymes, hypoxanthine formed in the trophoblast appears more likely to be re-utilized than degraded to uric acid.
利用密度梯度离心法，从酶解分散的孕早期和孕晚期胎盘混合细胞群中富集人滋养层细胞。回收的细胞中超过95% 来源于上皮细胞（即滋养层细胞），这通过间接免疫荧光检测其细胞角蛋白中间丝阳性和波形蛋白阴性得以证明，同时也通过其高含量的人绒毛膜促性腺激素得以证明。在滋养层细胞中测量了参与嘌呤降解和再利用的关键酶（5'-核苷酸酶、AMP脱氨酶、次黄嘌呤磷酸核糖转移酶（HPRT）、黄嘌呤脱氢酶/氧化酶）的活性以及碱性磷酸酶的总活性。孕早期和孕晚期之间，滋养层碱性磷酸酶活性增加了6倍。5'-核苷酸酶的活性下降了40%，基于动力学特性，该酶似乎在胎盘核苷5'-单磷酸的去磷酸化过程中起主要作用。AMP脱氨酶、HPRT和黄嘌呤脱氢酶/氧化酶的滋养层活性并不随孕周而变化。鉴于后两种酶的相对活性，滋养层中形成的次黄嘌呤似乎更有可能被再利用而不是降解为尿酸。
