Extraction of radioactive rubidium and D-glucose from the artificially perfused intervillous space of the human placenta

Influence of nicotinamide on the radiosensitivity of normal and goitrous thyroid in the rat

Radioiodine is used to treat thyroid cancer and hyperthyroidism. In order to reduce radiation hazard to the patient and to people in contact with the patient it would be desirable to obtain the same therapeutic effect with lower activities of the radioisotope. This could be achieved by the simultaneous administration of a compound that increases tissue radiosensitivity. In this study we analyzed the use of nicotinamide (NA) as a radiosensitizer to radioiodine, to increase 131I efficacy. NA administered during 30 days to Wistar rats failed to alter thyroid weight. The influence of NA on radiothyroidectomy induced by increasing doses of 131I was examined in otherwise nontreated rats. NA produced a significant increase in the ablation caused by radioiodine. Goiter was then induced by the administration of methylmercaptoimidazol (MMI) to rats, followed by the treatment with radioiodine with and without simultaneous administration of NA. Thyroid weight per 100 g of body weight ratio was not changed by NA alone; 131I administration caused a 25% decrease in goiter size, while 131I plus NA produced a reduction of the ratio of 46% (p < 0.01 vs. NA). No changes were observed in adenosine diphosphate (ADP)-ribosilation of thyroid nuclear protein in NA-treated rats. Thyroid blood flow (determined by 86Rb uptake) was increased by 84% by NA. In conclusion, nicotinamide has a significant radiosensitizing effect to 131I both in normal and goitrous rats. This action is because of an increase in thyroid blood flow, which probably enhances tissue oxgenation.

Parallel mechanisms of Ca++ transfer across the perfused human placental cotyledon

OBJECTIVES

We dissected the paracellular and transcellular components of Ca++ transfer across the perfused human placental cotyledon and explored the nature of the transcellular component.

STUDY DESIGN

Transfer of 45Ca++ and ethylenediaminetetraacetic acid labeled with chromium 51 was measured across the in vitro perfused cotyledon of the human placenta, and paracellular and transcellular components of the transfer of Ca++ were calculated from the transfer of the two tracers.

RESULTS

The transcellular component of the Ca++ transfer in the maternal-fetal direction represented about one third of the total maternal-fetal transfer. It was saturable, sensitive to cyanide, and insensitive to verapamil. The transcellular component in the fetal-maternal direction was not different from zero. The in vitro transfer rates correlated well with the transfer rates estimated for the in vivo situation from data published in the literature.

CONCLUSION

There is a significant active transport of Ca++ across the human placenta in the maternal-fetal direction.

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.