ABSTRACT
The primary objective of this study was to characterize an in-vitro model of the human placenta using morphological, biochemical and physiological parameters. Placental villi were obtained from normal first trimester and term pregnancies. The villi were incubated with Dulbecco's modified Eagle's medium: Ham's F12 nutrient mixture in a shaking water bath at 37 degrees C for up to 310 min. The viability was determined by the production of beta human chorionic gonadotrophin (HCG) and lactic dehydrogenase (LDH) and the incorporation of [3H]thymidine, [3H]L-leucine and L-[U14C]arginine, while ultrastructure was assessed by transmission electron microscopy. In the first and third trimester group, the release into the medium of the intracellular enzyme LDH remained unaltered throughout the experiment. By contrast, beta-HCG concentrations increased linearly and concentrations were higher in the first trimester than term villi (354.5 +/- 37.8 versus 107 +/- 8.1 IU/g villi protein; P < 0.001). Electron microscopy confirmed preservation of tissue viability for up to 4 h of incubation. The incorporation of thymidine (12.2 +/- 2.9 versus 5.2 +/- 0.5 nmol/g villi protein; P < 0.05), leucine (9.4 +/- 2.1 versus 1.9 +/- 0.4 nmol/g villi protein; P < 0.02) and arginine (17 +/- 4.4 versus 4.2 +/- 0.5 nmol/g villi protein; P < 0.05) were markedly higher in early than in term placenta. Furthermore, placental uptake of L-leucine by the first (9.4 +/- 2.1 versus 17 + 4.4 mol/g villi protein; P < 0.001) and third trimester placental villi (1.9 +/- 0.4 versus 4.2 + 0.5 mol/g villi protein; P < 0.001) was less than that of L-arginine. This study describes a simple technique using placental explants to determine relative rates of uptake of substrate amino acids throughout gestation.
