The artificially perfused guinea-pig yolk sac placenta: Transfer and uptake of water, glucose and amino acids

Abstract

The development of a new technique to investigate maternal fetal transfer across the near term guinea pig yolk sac placenta by in-situ perfusion of the yolk sac vessels is described. The maternal fetal transfer of labeled water, d- and l-glucose, O-methyl- d-glucose (oMDG), d- and l-alanine, d- and l-aspartate, L-lactate and alphaamino- isobutyric acid (AIBA) was investigated after injection of these substances into the maternal circulation. After 15 min of perfusion at 0.5 ml/min the water clearance was 132 ± 12 μ/ min ( SEM, n = 30). The clearances for d- or l-glucose were less than 1.2,μl/min. The activity of label in the venous yolk sac perfusate of all other substances was not different from background activity when 14C-label was used. The clearance of 3H- l-alanine approached the clearance value of water. The total uptake (as defined for single-injection double tracer dilution experiments) from the perfusate of d-glucose, oMDG, alanine and aspartate in comparison to l-glucose was also studied. Mean d-glucose uptake was 11.2 ± 1.9 per cent ( n = 8), it was significantly reduced to 4.9 ± 2 per cent ( n = 5) by cytochalasin B (1 × 10 −4 mmol/l), and by increasing concentrations of d-glucose (1 to 20 mmol/l, n = 4). The uptake of oMDG was 8.8 ± 1.5 per cent ( n = 8). l-alanine uptake was 25 ± 3.4 per cent, d-alanine uptake was 8.3 ± 1.5 per cent ( n = 12). Both uptake values were decreased significantly by 10 mmol/l l-alanine, but unaffected by [Na +] (< 15 mequ/l). There was no uptake of AIBA. The uptakes of l-aspartate were 34.9 ± 3.7 per cent and oft-aspartate 40.4 ± 4.8 per cent ( n = 11). Both uptake values were significantly and reversibly reduced by 1 mmol/l l-aspartate and d-aspartate, and by low [Na +] (< 15 mequ/l). It is concluded that water can move by diffusion from maternal circulation into the yolk sac capillaries in considerable amounts whereas the contribution of the yolk sac placenta to fetal nutrition with d-glucose, l-alanine and l-aspartate is negligible. The membranes of yolk sac cells contain specific transport systems for d-glucose, d-/l-alanine and d-/l-aspartate transfer. The function of the vitelline placenta in the near-term guinea-pig is comparable more to the gut than to the chorio-allantoic placenta.