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Biomedical subjects

J Stulc

Publications and source records attributed to J Stulc.

43 records · Page 3Linked to original sources
PubMedDate not supplied

Transport of radioactive deoxyglucose by the isolated perfused human placental cotyledon as measured by the paired-tracer dilution method. Inconsistency of the transfer rates across the two trophoblast borders with the simultaneously measured rate of transplacental transfer.

The uptake of [3H]2-deoxy-D-glucose ([3H]2DG) by the maternal and fetal borders of the trophoblast was measured in the dually perfused human placental cotyledon by use of the paired-tracer dilution method. The uptake was estimated from the maximum extraction of the tracer. The transcellular component of transplacental transport of [3H]2DG was measured simultaneously. From the rates of uptake by the two trophoblast borders the rate of transcellular transport was predicted. The rate predicted was significantly lower than the rate observed. This was taken to indicate that the paired-tracer dilution method based on the maximum extraction underestimated the rates of uptake.

Biological Transport↗
PubMedDate not supplied

Effect of maternal hypokalaemia on unidirectional maternofetal and net potassium fluxes across the placenta of the anaesthetized rat.

Potassium (K+) fluxes across the placenta of rats, at 21 days gestation, fed a low K+ diet or a control diet were studied. The rats on the low K+ diet had a significantly (P less than 0.001) lower arterial plasma K+ concentration compared to those on the control diet (1.95 +/- 0.12 and 2.93 +/- 0.06 mmol/l respectively; mean +/- s.e., n = 17). Fetal umbilical arterial plasma K+ concentration was unaltered in maternal hypokalaemia and was significantly (P less than 0.001) higher than that of maternal plasma (4.58 +/- 0.15 and 4.66 +/- 0.12 mmol/l in low K+ and control groups respectively). Net K+ flux across the placentas (as measured by fetal accretion between days 20 and 21 of gestation) of hypokalaemic mothers (0.106 +/- 0.02 mumol/min/g placenta, n = 6) was not different to that in controls (0.104 +/- 0.01 mumol/min/g placenta, n = 8). Unidirectional maternofetal flux (Jmf) across the placentas, measured as the accumulation of 42K in the fetuses after injection of the radioisotope into maternal blood, was also not significantly different between the hypokalaemic and control mothers (0.5 +/- 0.08 mumol/min/g placenta, n = 8 versus 0.63 +/- 0.06 mumol/min/g placenta, n = 7, respectively). However, measurement of Jmf by perfusion of the placentas through their fetal circulations yielded a higher value than the accumulation method and in this analysis was significantly (P less than 0.02) lower in the low K+ than in the control group (0.75 +/- 0.10 mumol/min/g placenta, n = 11, and 1.27 +/- 0.14 mumol/min/g placenta, n = 9, respectively). These results show that net placental K+ fluxes are unaltered during maternal hypokalaemia but suggest that unidirectional maternofetal fluxes may be reduced.

Animals↗
PubMedDate not supplied

Transport of inorganic phosphate by the fetal border of the guinea-pig placenta perfused in situ.

Unidirectional flux of inorganic phosphate, Pi, from the umbilical vascular bed perfused in situ into the cell compartment of the guinea-pig placenta, Jfc , was estimated using the indicator dilution method, with 32P-phosphate and 14C-sucrose as the tracers. The flux did not depend on fetal weight; its mean value was 0.25 +/- 0.02 mumol/min (s.e., n = 19). Jfc decreased when the placenta was perfused with CN (10(-3)M) or with Na-free fluid. Elevation of the Pi concentration in the perfusate caused an increase in Jfc which, however, was not proportional. These properties of Jfc were taken to be compatible with a Na-dependent active transport mechanism. The flux in the opposite direction, Jcf , correlated with the fetal weight. It decreased when the umbilical concentration of Pi was elevated. The efflux of 32P from placentae preloaded with the tracer changed inversely with the umbilical concentration of Pi. It is concluded that there is a bidirectional transcellular transfer of Pi between the two sides of the placenta, the flux in the maternal-fetal direction being the prevailing one. The unidirectional transfer to the fetus seems to be regulated directly by the umbilical concentration of Pi.

Animals↗
PubMedDate not supplied

Extracellular binding of calcium in the guinea-pig placenta.

Extraction of 45Ca from the perfused umbilical vascular bed of the guinea-pig placenta was measured using 3H-sucrose or 24Na as reference substances at a constant inflow concentration of the tracers. La3+ (5mM) depressed extraction of 45Ca below zero for several minutes. This suggests that there is a significant amount of Ca bound extracellularly on the umbilical side of the placental barrier.

Animals↗