Transfer Of Antipyrine Research Articles

Placental transfer of doravirine, a recent HIV-1 NNRTI in the ex vivo human cotyledon perfusion model.

The recent HIV-1 NNRTI doravirine is likely to be used in pregnant women despite the complete lack of data on safety and exposure in the fetus. The objective of this study was to determine its placental transfer. Maternal-to-fetal transfer was investigated using the open-circuit ex vivo dually perfused human cotyledon model. Doravirine was added to a maternal perfusate (theoretical doravirine concentration of 250 ng/mL) containing 2 g/L human albumin and 20 g/L antipyrine, a marker to validate the cotyledon's viability, and cotyledons were dually perfused for up to 90 min. In five experiments, the median (IQR) doravirine concentrations in the maternal and fetal compartments were, respectively, 303 (178-420) and 40 (30-54) ng/mL, the fetal-to-maternal ratio was 16% (12%-18%) and the clearance index (in comparison with antipyrine transfer) was 48% (35%-64%). The median accumulation index in cotyledon tissue was 39% (range 10%-66%). Doravirine both crosses and accumulates in the placenta. This may be useful as pre/post-exposure prophylaxis to reduce the risk of vertical HIV transmission but carries the potential for fetal toxicities. Further investigation is required to determine the safety and efficacy of this new antiretroviral agent in pregnancy.

Placental transfer of the integrase strand inhibitors cabotegravir and bictegravir in the ex-vivo human cotyledon perfusion model.

: Data on placental transfer is lacking for the recent HIV integrase inhibitors, bictegravir and cabotegravir, although their future use in pregnancy is to be expected. The objective of this study was to determine their transplacental pharmacokinetics. Maternal-to-fetal transfer was investigated using the open-circuit ex-vivo dually perfused human cotyledon model. Cabotegravir or bictegravir was added to a maternal perfusate containing 2 g/l of human albumin and antipyrine, a marker to validate the cotyledon's viability, and cotyledons were dually perfused for up to 90 min. For cabotegravir, in five experiments, the median (IQR 25-75) concentrations in the maternal and in the fetal compartments were, respectively, 550 ng/ml (344-788) and 48 ng/ml (37-54), with a maternal-to-fetal ratio of 10% (5-16) and a clearance index (in comparison with antipyrine transfer) of 22% (19-28). The median cotyledon accumulation index was 10% (2-21). For bictegravir, in six experiments, the median (IQR 25-75) concentrations in the maternal and in the fetal compartments were, respectively, 1650 ng/ml (1455-1960) and 126 ng/ml (112-142), with a maternal-to-fetal ratio of 7% (6-9.5) and a clearance index (in comparison with antipyrine transfer) of 21% (17-29). The median cotyledon accumulation index was 4% (3-5). Placental transfer of cabotegravir and bictegravir were low. This may not only limit the potential for fetal toxicities but also be a limit to their usefulness at the time of labor and delivery to reduce the risk of vertical HIV transmission. The safety and efficacy of these new integrase inhibitors in pregnancy require more investigation.

Placental transfer and tissue accumulation of dolutegravir in the ex vivo human cotyledon perfusion model

ObjectiveTo determine the transplacental pharmacokinetics of the HIV integrase inhibitor dolutegravir.Study designMaternal-to-fetal transfer across the term human placenta was investigated with the ex-vivo dually perfused cotyledon model, in 5 closed-circuit, recirculating experiments. Dolutegravir was added to a maternal perfusate containing antipyrine, a marker to validate the cotyledon’s viability, and 2 g/liter of human albumin.ResultsAfter 3h of recirculating perfusion, the mean (± SD) DTG concentrations in the maternal and in the fetal compartments were respectively 2450 ± 286 ng/mL and 715 ± 369 ng/mL, with a fetal-to-maternal ratio of 34% ± 18% and a clearance index (in comparison with antipyrine transfer) of 79% ± 23%. The mean cotyledon accumulation index was 153% ± 25%.ConclusionFetal transplacental exposure to dolutegravir was considerable as well as accumulation in placental tissue. Whether this may lead to risks for the exposed fetus requires more investigation.

Criteria and challenges of the human placental perfusion – Data from a large series of perfusions

Perfusion of human placental cotyledon has been used extensively to study transplacental transfer of endogenous and exogenous compounds. However, many challenges in the use of the method exist, including availability of placentas and complexity of the method itself. In Kuopio, Finland we have carried out human placental perfusions since 2005 using the same method with data now from over one hundred perfusions. This has allowed us to study whether the way of delivery, placental weight, and/or the length of pregnancy affect the two major criteria of a successful perfusion: volume loss (leak) from fetal to maternal circulation, and transplacental transfer of the reference compound antipyrine. The only statistically significant result was the reduction of the fetomaternal ratio of antipyrine by the placental age over 40weeks (p=0.0004). The success criteria were not affected by the weight of the placenta or the way of delivery. There was no effect by the antipyrine concentration on antipyrine transfer. In vitro incubation with different concentrations of study compounds and different tubing materials could offer an easy way to study potentially reduced recovery due to binding to perfusion system.

Meta-analysis of data from human ex vivo placental perfusion studies on genotoxic and immunotoxic agents within the integrated European project NewGeneris

In the EU integrated project NewGeneris, we studied placental transport of thirteen immunotoxic and genotoxic agents in three ex vivo placental perfusion laboratories. In the present publication, all placental perfusion data have been re-analyzed and normalized to make them directly comparable and rankable. Antipyrine transfer data differed significantly between the studies and laboratories, and therefore normalization of data was necessary. An antipyrine normalization factor was introduced making the variance significantly smaller within and between the studies using the same compound but performed in different laboratories. Non-normalized (regular) and normalized data showed a good correlation. The compounds were ranked according to their transplacental transfer rate using either antipyrine normalized AUC120 or transfer index (TI120(%)). Normalization generated a division of compounds in slow, medium and high transfer rate groups. The transfer rate differed slightly depending on the parameter used. However, compounds with passage similar to antipyrine which goes through the placenta by passive diffusion, and good recovery in media (no accumulation in the tissue or adherence to equipment) were highly ranked no matter which parameter was used. Antipyrine normalization resulted in the following ranking order of compounds according to AUC120NORM values: NDMA ≥ EtOH ≥ BPA ≥ IQ ≥AA ≥ GA ≥ PCB180 ≥ PhIP ≥ AFB1 > DON ≥ BP ≥ PCB52 ≥ TCDD. As the variance in all parameters within a study decreased after antipyrine normalization, we conclude that this normalization approach at least partially corrects the bias caused by the small methodological differences between studies.

Differential Bidirectional Transfer of Indinavir in the Isolated Perfused Human Placenta

The protease inhibitor (PI) indinavir may be used in the management of human immunodeficiency virus (HIV) infection during pregnancy. Poor maternal-to-fetal transfer of indinavir has been reported previously, but the mechanisms of transfer remain unknown. The bidirectional transfer of indinavir was assessed in dually perfused, isolated human placentae. Term placentae (n = 5) were obtained from non-HIV-infected pregnant women. To investigate transport mechanisms, the steady-state transfer of indinavir was compared to those of antipyrine (a marker of passive diffusion) and [(3)H]vinblastine (a marker of P-glycoprotein [P-gp] transport) in the maternal-to-fetal and fetal-to-maternal directions in each placenta. Indinavir and antipyrine perfusate concentrations were determined by using reverse-phase, high-performance liquid chromatography; [(3)H]vinblastine concentrations were measured by liquid scintillation. The antipyrine transfer clearance in each direction did not differ (P = 0.76), a finding consistent with passive diffusion. However, the maternal-to-fetal transfer clearance of vinblastine, normalized to that of antipyrine (clearance index) (0.31 +/- 0.05), was significantly lower than the fetal-to-maternal clearance index of vinblastine (0.67 +/- 0.17; P = 0.017), suggesting the involvement of placental P-gp. Similarly, the maternal-to-fetal clearance index of indinavir (0.39 +/- 0.09) was significantly lower than its fetal-to-maternal clearance index (0.97 +/- 0.12; P < 0.001). These results represent the first evidence for differential transfer of a xenobiotic in the intact human placenta. The use of transport modulators to increase the maternal-to-fetal transfer of PIs as a possible strategy to reduce mother-to-child transmission of HIV warrants investigation.

Transplacental transfer of citalopram, fluoxetine and their primary demethylated metabolites in isolated perfused human placenta

Objective To investigate the transplacental transfer and the effects of protein binding on the transfer of citalopram, desmethylcitalopram, fluoxetine and desmethylfluoxetine in the isolated perfused human placenta model. Design Prospective observational study. Methods Fifteen term human placentas were obtained immediately after delivery with maternal consent and a 2-hour non-recirculating perfusion cycle of a single placental cotyledon was set up. Citalopram (1230 nmol/L) and desmethylcitalopram (600 nmol/L) or fluoxetine (1455 nmol/L) and desmethylfluoxetine (1525 nmol/L) were added to the maternal reservoir and their appearance to the fetal circulation was followed by repeated measurements. To investigate the effect of protein binding on the transfer of citalopram and fluoxetine, nine additional perfusions were performed without albumin in the perfusion medium. Citalopram and desmethylcitalopram concentrations were measured by reversed-phase high performance liquid chromatography. Fluoxetine and desmethylfluoxetine concentrations was measured by gas chromatography and antipyrine (used as a reference compound) concentrations spectrophotometrically. Results The mean (SD) steady-state transplacental transfer (TPT SS%) for citalopram, desmethylcitalopram, fluoxetine and desmethylfluoxetine was 9.1%, 5.6% ( P = 0.017 compared with citalopram), 8.7% and 9.1%, respectively, calculated as the ratio between the steady-state concentrations in fetal venous and maternal arterial sides. The TPT SS%s of citalopram, desmethylcitalopram, fluoxetine and desmethylfluoxetine were 86%, 50%, 88% and 91% of that of freely diffusable antipyrine. The absence of albumin significantly reduced the transfer of citalopram and fluoxetine (TPT SS% 1.1% and 4.8%, respectively) but not the transfer of antipyrine. Conclusion Citalopram, fluoxetine and desmethylfluoxetine all cross the human placenta, and may, therefore, affect the perinatal outcome of infants exposed to these drugs during pregnancy. The transfer of desmethylcitalopram was significantly lower, which in the clinical setting may suggest lower fetal exposure of serotonin re-uptake inhibition by citalopram compared with fluoxetine. The presence of albumin was necessary for the transplacental transfer of both citalopram and fluoxetine.

The effects of uterine and umbilical blood flows on the transfer of propofol across the human placenta during in vitro perfusion.

The safety of using propofol in parturients is controversial, and little information is available on the factors that influence the placental transfer of propofol. In this study, we investigated the effects of uterine and umbilical blood flows on the placental transfer of propofol by using the dually perfused human placental cotyledon. Placental transfer was evaluated on the basis of the placental clearances at various uterine and umbilical flow rates. The placental transfer of propofol was significantly facilitated by the increased uterine flow rates over the range from 7.5 to 25 mL/min. The placental clearances of propofol were also dependent on the umbilical flow rates over the range from 0.5 to 4.0 mL/min. In contrast, the placental transfer of antipyrine was flow dependent when the umbilical flow rate was <2.0 mL/min and became permeability limited when it was >2.0 mL/min. No differences in either maternal or fetal venous concentrations of propofol were observed as umbilical flow rates varied from 0.5 to 4.0 mL/min, suggesting that an equilibration across the placenta occurs at low flow rates. These results indicate that fetal uptake of propofol can be profoundly altered by the changes in both uterine and umbilical blood flows observed in various pathophysiologic conditions and that lipid solubility greatly influences placental transfer of drugs. Uterine and umbilical blood flows are determinant features in controlling the placental transfer of propofol, and, therefore, changes in these variables would significantly affect the extent of fetal exposure to propofol.

Transplacental transfer of amitriptyline and nortriptyline in isolated perfused human placenta.

Although tricyclic antidepressants (TCAs) have gained wide acceptance for use in the treatment of depression in pregnant women, their pharmacokinetics during pregnancy have been poorly characterized. The aim of the present study was to investigate the transplacental transfer of amitriptyline (AMI) and its main active metabolite nortriptyline (NOR) in isolated perfused human placenta. Nine term human placentae were obtained immediately after delivery with maternal consent and a 2-h non-recirculating perfusion of a single placental cotyledon was performed. AMI (200 ng/ml) and NOR (150 ng/ml), with antipyrine as a reference compound, were added to the maternal reservoir and their appearance to the fetal circulation was followed for 2 h. AMI and NOR concentrations were measured by high performance liquid chromatography (HPLC) and antipyrine concentrations spectrophotometrically. The mean (SD) transplacental transfers (TPT(SS)%) for AMI and NOR were 8.2 (2.3)% and 6.5 (1.8)%, respectively, calculated as the ratio between the steady-state concentrations in fetal venous and maternal arterial sides. The TPTs of AMI and NOR were 81% and 62% of the freely diffusable antipyrine. The absolute fraction of the dose that crossed the placenta (TPT(A)) was moderately, but significantly higher for AMI (7.7%) than for NOR (5.7%) (P=0.037). In all perfusions, steady state at the fetal side was reached by 30 min for AMI and by 50 min for NOR in the fetal side. The viability of the placentae was retained during the 2-h perfusion, as evidenced by unchanged pH of the perfusate and by stable perfusion pressures in fetal artery and stable antipyrine transfer. Both AMI and NOR cross the human placenta. However, the fetal exposure with NOR may be somewhat smaller compared with AMI, probably due to the higher lipophilicity of AMI.

Pharmacokinetics of oxcarbazepine and carbamazepine in human placenta.

To study the transfer and metabolism of oxcarbazepine (OCBZ) and 10-hydroxy-10,11-dihydrocarbamazepine (10-OH-CBZ) and carbamazepine (CBZ) metabolism and its possible induction in human placenta. A dual recirculating human placental perfusion system, blood sampling, high performance liquid chromatography (HPLC), reverse transcriptase-polymerase chain reaction (RT-PCR), and enzyme assays. OCBZ was metabolized into 10-OH-CBZ in five human placental cotyledons perfused for 2 h in a dual recirculating perfusion system. The same metabolite was found by HPLC in three sample pairs of maternal and cord blood taken during delivery from patients on OCBZ therapy. In all of the clinical samples, 10,11-trans-dihydroxy-10,11-dihydrocarbamazepine (10,11-D) was also found, but not in the perfusions. In addition, 10-OH-CBZ was not metabolized in the placental perfusions. The transfer of OCBZ through the perfused placentas was quicker than the transfer of antipyrine, while the transfer of 10-OH-CBZ was slower. Both OCBZ and 10-OH-CBZ also accumulated in placental tissue. CBZ metabolism was studied in three perfusions using placentas from mothers on CBZ therapy. No metabolism could be detected in the perfused placentas, while metabolites were found in both maternal and cord blood of the same mothers. Another series of placentas of mothers on CBZ therapy did not differ significantly from the placenta of a healthy mother as to CYP activities or the level of CYP3A4 mRNA. OCBZ is metabolized into 10-OH-CBZ to some extent in human placenta in vitro, suggesting that the placenta also participates in the metabolism of OCBZ in vivo. On the contrary, the placenta does not participate in the metabolism of CBZ. No induction of placental CBZ metabolism in vitro can be detected after maternal CBZ treatment during pregnancy.

Transfer of clonidine and dexmedetomidine across the isolated perfused human placenta.

The placental transfer of the alpha 2 receptor agonist clonidine, earlier used as an adjuvant in obstetric epidural analgesia, was compared with the transfer of the newer and more alpha 2-selective agonist dexmedetomidine. Term placentas were obtained immediately after delivery with maternal consent and a 2-hour recycling perfusion of a single placental cotyledon was performed. Disappearance from the maternal circulation, accumulation in placental tissue and appearance in the fetal circulation of clonidine or dexmedetomidine with the reference compound antipyrine were followed in 4 experiments for both drugs. At 2 hours the percent dexmedetomidine found in the fetal circulation was 12.5 (SD 5.1)%, while 48.1 (SD 20.3)% was found in the perfused placental cotyledon. A higher mean clonidine than dexmedetomidine concentration was achieved in the fetal circulation (1.90 vs. 0.56 nmol/l, P < 0.05). At 2 hours the percent clonidine found in the fetal circulation was 22.1 (SD 2.4)% (P < 0.05), while 11.3 (SD 3.3)% (P < 0.05) was retained in the perfused placental cotyledon. The transfer indexes, describing maternal-to-fetal transfer of dexmedetomidine and clonidine normalized with the transfer of antipyrine, were 0.88 (SD 0.07) and 1.04 (SD 0.08) respectively (P < 0.05). Dexmedetomidine disappeared faster than clonidine from the maternal circulation, while even less dexmedetomidine was transported into the fetal circulation. This was due to its greater placental tissue retention, the basis for which probably is the higher lipophilicity of dexmedetomidine.

Effects of fetal pH on local anesthetic transfer across the human placenta.

Fetal acidemia increases umbilical venous bupivacaine concentrations in the in situ rabbit model. The authors studied the effects of decreasing fetal pH on the rate of maternal to fetal (M-->F) clearances of lidocaine, bupivacaine, 2-chloroprocaine, and antipyrine (a nonionic marker of placental transfer) across the isolated, dual perfused, human placental cotyledon. Maternal to fetal clearances of bupivacaine, lidocaine, 2-chloroprocaine, and antipyrine were determined at fetal pH (7.4), during progressive fetal acidemia (pH 7.2-->7.0-->6.8), and after recovery to fetal pH 7.4 in experiments with both low protein state and in those with in vivo maternal and fetal protein-binding potentials. Placental transfer of all three agents increased linearly as the fetal pH decreased. Antipyrine transfer was unaffected. Clearance of lidocaine and bupivacaine, but not 2-chloroprocaine, returned to baseline when fetal pH was restored to 7.4. When maternal and fetal protein-binding potentials were increased, clearance at fetal pH 7.4 of bupivacaine, but not lidocaine, decreased significantly. During fetal acidemia, the transfer of both agents increased, but to a lesser extent than in the low protein concentration experiments. Increasing the pH difference between maternal and fetal perfusates promotes M-->F passage of unionized lidocaine, bupivacaine, and 2-chloroprocaine. This likely results from an increased proportion of ionized local anesthetic in the acidemic fetal perfusate and consequent widening of the M-->F concentration gradient of the unionized form. Transfer of lidocaine and bupivacaine was limited by the maternal protein binding.

The transfer of interleukin-8 across the human placenta perfused in vitro

To assess the placental transfer of interleukin (IL)-8 in vitro. Eighteen placentas obtained immediately after delivery were perfused with a mixture of 125I-labeled IL-8 (IL-8*) and unlabeled IL-8 in two different concentrations. Antipyrine was coinfused in all experiments as a reference compound. Fetal-to-maternal and maternal-to-fetal perfusions were performed. Radioactivity was measured in a gamma counter at the end of each perfusion experiment. In four experiments, unlabeled IL-8 was analyzed in addition to labeled IL-8 to exclude a change in the IL-8/IL-8* ratio resulting from membrane transfer. Two of the 18 experiments had to be discarded because of poor transfer of antipyrine. There was only faint accumulation of radioactivity in the transplacental compartment, regardless of whether the test substance was added maternally or fetally. Because measurement of unlabeled IL-8 yielded negative results, the radioactivity is clearly attributable to free iodine 125, which is generated during IL radiolabeling or which disassociates from IL-8 in small amounts after radiolabeling. Interleukin-8 does not appear to cross the placenta by simple diffusion, regardless of the concentration or the perfusion rate. The impermeability of the placenta to the diffusion of IL-8 might explain why there is insufficient correlation between serum and amniotic fluid cytokine concentrations of pregnant women and the presence of the amnion infection syndrome.

Carbamazepine and Its Metabolites in Human Perfused Placenta and in Maternal and Cord Blood

Placental transfer and metabolism of carbamazepine (CBZ) was studied in a dual recirculating placental cotyledon perfusion system and was also evaluated in 16 pairs of maternal venous and cord blood samples. Among the parameters studied as possible indicators of a successful perfusion, volume changes in perfusate divided the perfusions into two groups, whereas no significant differences between perfusions were noted in blood gas analysis or in antipyrine transfer. CBZ added into the maternal circulation crosses the placenta in the beginning quicker than antipyrine which is in agreement with the different lipid solubilities of these compounds. Because the transfer rates of antipyrine and CBZ were about the same, the mechanism of transfer of CBZ is probably similar to that of antipyrine (passive diffusion). No metabolites of CBZ could be detected in the perfusate by high-performance liquid chromatography (HPLC) or gas chromatography/mass spectrometry. With the improved HPLC methodology for CBZ metabolites, six metabolites were detected in clinical samples, including 10-hydroxy-10,11-dihydro-CBZ (10-OH-CBZ), which has been described earlier in only 1 uremic patient. Relative levels of metabolites showed significant individual differences. CBZ crosses perfused placenta rapidly, but this does not contribute to CBZ metabolites detected in maternal and fetal circulation.

Effect of inorganic mercury on in vitro placental nutrient transfer and oxygen consumption

The effect of mercury (HgCl 2) on placental amino acid and glucose transfer as determined by the use of their nonmetabolizable radioactive analogues, aminoisobutyric acid (AIB) and 3- o-metyhl glucose (3MG), respectively, was studied in an in vitro perfusion model of a term human placenta. Hg 2+ was found to decrease the transfer and accumulation of AIB without affecting 3MG transfer. It was also found to decrease the placental oxygen consumption rate. Placental circulation and tissue morphology remained intact, as demonstrated by the antipyrine transfer rate, and by electron microscopy, respectively. The mechanism by which Hg 2+ may interfere with placental amino acid transfer and accumulation is discussed. Although much higher concentrations than those found in the ordinary polluted environment were used, this is the first report showing that Hg 2+ interferes with an essential human placental function in a system employing a whole human placental cotyledon. This finding may indicate the possible involvement of Hg 2+ in impaired organogenesis in early pregnancy or deranged fetal growth during the last trimester.

Transplacental Transfer of Ritodrine and Its Effect on Placental Glucose and Oxygen Consumption in an in vitro Human Placental Cotyledon Perfusion

Maternofetal transfer of ritodrine and its effect on placental glucose and oxygen consumption were studied using a recycling perfusion of maternal and fetal circulations of an isolated cotyledon of a term human placenta. 3H-labeled ritodrine was introduced into the maternal side of the perfusion system. Transfer was calculated from the linear rise of ritodrine concentrations on the fetal side and was found to be 7.31 +/- 1.02 ng/g placental wet weight/min (SEM) when 1.4 micrograms/ml of ritodrine was used (n = 3) and 14.7 +/- 1.06 ng/g placental wet weight/min when the concentration was 2.8 micrograms/ml (n = 5). The antipyrine transfer rate, 4.1 +/- 0.51 mg/kg/min (n = 8), was used to demonstrate perfusion adequacy and served as an internal standard. Upon computing the mass balance of ritodrine and antipyrine at the end of the experiment, it was found that 17% of ritodrine disappeared from the perfusion system compared to 0.7% of antipyrine (p less than 0.01). The introduction of ritodrine into the perfusion system did not affect placental glucose and oxygen consumption rates of 0.35 +/- 0.01 mumol/g/min (n = 7) and 0.19 +/- 0.013 mumol/g/min (n = 5), respectively.

Effects of pH on Antipyrine Transfer across the Human Placenta ex vivo

The influence of pH variations on transplacental transfer of antipyrine was studied using a human placental cotyledon perfused ex vivo. The antipyrine transfer rate is positively correlated with the pH in the fetal circulation and negatively correlated with the pH in the maternal circulation. Thus, the transfer rate is negatively correlated with the difference between pH values in maternal and fetal circulations. The antipyrine transfer rate is also positively correlated with the flows in maternal and fetal circulations. The above parameters allowed to explain 50% of the variance on the transfer rates obtained in various experimental conditions. In a final series of experiments where these parameters for each placenta were fixed at identical values, a good reproducibility in the results was obtained, the variation coefficient being 17%. Thus, establishing the effect of variations in pH allowed a good standardization of the perfused cotyledon model. This effect cannot be explained by modifications in the ionized fraction of the antipyrine molecular and is probably due to physiological mechanisms.

Flow-dependent transfer of antipyrine in the human placenta in vitro.

Placental transfer of antipyrine, a small liposoluble molecule, was investigated at varying flow rates using dual perfusion of human placental lobules. With a flow ratio equal to unity, the foetal transport fraction (foetal vein concentration X 100/maternal artery concentration) of antipyrine averaged 0.33. It has been suggested that effectiveness of exchange in the lobule perfused in vitro approximated that of a concurrent model with an antipyrine 'd' coefficient between 0.6 and 1.2, including shunting which diverted 16 p. 100 of foetal and 13 p. 100 of maternal flow rates from the exchange area. These observations have been discussed in relation to data obtained in other mammalian placentas and in man in vivo.

The transfer and metabolism of corticosteroids in the perfused human placenta

The transfer and metabolism of cortisol, prednisolone, betamethasone, and dexamethasone were investigated in vitro in the perfused human placenta. Maternal and fetal circuits were established but the steroid was added to the former only. The clearance expressed as a fraction of the antipyrine transfer rate varied from 0.27 to 0.50, but there were no significant differences among the four steroids. All the steroids were metabolized extensively to their respective 11-ketosteroids and again there were no material differences among the steroids. The metabolic conversions of dexamethasone and betamethasone were far greater in the perfused placenta than in minced placenta. From the standpoint of placental transfer and metabolism, as observed in the perfusion studies, none of the four corticosteroids offers a decisive advantage in the antepartum maturation of the fetal pulmonary surfactant system.

Effect of Protein Binding on Transfer and Metabolism of Cortisol in Perfused Human Placenta*

The transfer and metabolism of cortisol and cortisone and the effect of protein binding on these processes have been investigated in vitro in the perfused human placenta. The clearance of cortisol in buffer, expressed as a fraction of the antipyrine transfer rate (clearance index), was 0.50 +/- 0.05 SEM in either direction. Extensive conversion to cortisone (85%) occurred during transfer. Addition of corticosteroid-binding globulin (CBG) in amounts sufficient to bind 50% of the cortisol reduced the clearance (0.40 +/- .026) insignificantly, whereas human serum albumin (HSA) in amounts sufficient to bind 50% of the cortisol reduced the clearance to 0.28 +/- 0.012 (P less than 0.001) even though the association constant for albumin is approximately 1000-fold less. The percent of conversion to cortisone did not change significantly with protein binding. The clearance index of cortisone from a protein-free perfusate was 0.74. With CBG and albumin in the same concentrations as used in the cortisol experiments, the binding of cortisone to CBG was 23% and its clearance was 0.70; with albumin, the binding was 45% and the clearance index was 0.45. The addition of albumin and CBG to the same perfusate resulted in a cortisol clearance equal to that obtained with perfusate containing only albumin. Binding to albumin may be more significant than binding to CBG in controlling the transfer rate of cortisol to the fetus.