The actions of prostaglandins and their interactions with angiotensin II in the isolated perfused human placental cotyledon

The prostaglandins PGE1, PGE2, PGD2, PGF2 alpha, U46619 and 6 beta-PGI1 were administered as bolus injections both separately and in combination with angiotensin II into the fetal circulation of isolated human placental cotyledons perfused in vitro. PGF2 alpha and PGD2 caused small dose-dependent increases in fetal perfusion pressure when compared with U46619 which acted as an extremely potent vasoconstrictor of the fetal-placental vasculature. PGE1 caused very small dose-dependent decreases in fetal perfusion pressure when injected on its own. In combination with angiotensin II, PGE1, PGD2 and 6 beta-PGI1 caused significant, dose-related attenuations of the angiotensin II vasoconstrictive response whereas PGE2, PGF2 alpha and U46619 potentiated the response. Injections of angiotensin II after the infusion of indomethacin into the fetal circulation resulted in a potentiation of angiotensin II induced vasoconstriction. The results indicate that prostaglandins exert their effects on the fetal-placental circulation by modulating the actions of angiotensin II.     

The actions of prostaglandins and their interactions with angiotensin II in the isolated perfused human placental cotyledon

Summary. The prostaglandins PGE₁, PGE ₂, PGD ₂, PGF _2α., U46619 and 6_β-PGI_l were administered as bolus injections both separately and in combination with angiotensin II into the fetal circulation of isolated human placental cotyledons perfused in vitro . PGF_2α, and PGD₂, caused small dosedependent increases in fetal perfusion pressure when compared with U46619 which acted as an extremely potent vasoconstrictor of the fetal-placental vasculature. PGE₁, caused very small dose-dependent decreases in fetal perfusion pressure when injected on its own. In combination with angiotensin 11, PGE₁, PGD₂, and 6_β-PG1₁, caused significant, dose-related attenuations of the angiotensin II vasoconstrictive response whereas PGE₂, PGF_2α, and U46619 potentiated the response. Injections of angiotensin II after the infusion of indomethacin into the fetal circulation resulted in a potentiation of angiotensin II induced vasoconstriction. The results indicate that prostaglandins exert their effects on the fetal-placental circulation by modulating the actions of angiotensin II.     

Prostaglandin production and stimulation by angiotensin II in the isolated perfused human placental cotyledon

Levels of prostaglandins E and F2 alpha, thromboxane B2, and 6-oxo-prostaglandin F1 alpha were measured by radioimmunoassay in the maternal and fetal effluents of isolated human placental cotyledons perfused in vitro. All prostaglandins measured were released in greater amounts by the maternal side than by the fetal side of the perfused cotyledon although there were no consistent concentration gradients between the two sides. The approximate rank order of prostaglandin release into the maternal side was thromboxane B2 greater than prostaglandin F2 alpha congruent to prostaglandin E congruent to 6-oxo-prostaglandin F1 alpha, and that into the fetal side was thromboxane B2 congruent to prostaglandin F2 alpha congruent to prostaglandin E congruent to 6-oxo-prostaglandin F1 alpha. Injection of angiotensin II (0.5 microgram) into the fetal circulation stimulated prostaglandin E and 6-oxo-prostaglandin F1 alpha but not thromboxane B2 and prostaglandin F2 alpha release into the fetal circulation and had no effect on maternal release. Angiotensin II (0.5 microgram) had no effect on either side of the perfused cotyledon when injected into the maternal circulation. It is proposed that prostaglandin release into both maternal and fetal circulations may be flow-dependent and that the angiotensin II-stimulated release of prostaglandin E and 6-oxo-prostaglandin F1 alpha may serve to modulate the vasoactive actions of angiotensin II on the fetal vasculature.     

Condition and performance of the perfused human placental cotyledon

The perfused human placental cotyledon was examined with respect to its viability, metabolic state, and performance. During the ischemic period before the start of perfusion, tissue adenosine triphosphate concentration and other measures of energy state fell rapidly to about half of the estimated in vivo value. During the subsequent perfusion, energy levels remained relatively stable but did not recover appreciably toward in vivo values. A very low transplacental leakage of inulin and a small cellular potassium loss indicate relative intactness of membrane function, but there were differences from the in vivo state in levels and balance of metabolic regulators adenosine triphosphate, adenosine monophosphate, and adenosine triphosphate/adenosine monophosphate ratio, and a more reduced cytoplasmic reduced nicotinamide adenine dinucleotide/ionized nicotinamide adenine dinucleotide couple. However, rates of oxygen and glucose consumption and lactate production and the maintenance of physiologic upward maternal-to-fetal concentration gradients of amino acids lead us to conclude that despite differences in energy and metabolic states the perfused cotyledon remains substantially intact and functions in certain respects comparably with the in vivo state.     

The effects of the components of the renin-angiotensin system on the isolated perfused human placental cotyledon

Angiotensins I, II, and III, renin substrate, and des-Asp¹-angiotensin I were injected as a bolus into either the maternal or fetal circulation of human placental cotyledons perfused in vitro. All drugs tested produced dose-related increments in fetal perfusion pressure when injected into the fetal circulation, with the order of potency being angiotensin I ≈ angiotensin II ≈ angiotensin III ? des-Asp¹-angiotensin I ? renin substrate. The responses to all the drugs could be blocked by the competitive inhibitor of angiotensin II, (Sar¹, Ala⁸)-angiotensin II, but only the actions of angiotensin I, renin substrate, and des-Asp¹-angiotensin I could be blocked by angiotensin converting enzyme inhibitor. When the agents were injected into the maternal circulation, only angiotensins II and III caused dose-related increments in fetal perfusion pressure. Possibly, the placenta may be the main site of conversion of angiotensin I to angiotensin II in the fetoplacental unit, and angiotensin II produced by the placenta could act locally to control fetoplacental blood flow.     

The effect of magnesium sulfate on the placental corticotropin-releasing factor (CRF) and CRF binding protein mRNA expression in perfused human placental cotyledon

Objectives: Stress stimuli and inflammation influence the secretion of the placental corticotropin-releasing factor CRF (CRF) that has a significant role in controlling the timing of birth. The CRF-binding protein (CRF-BP) binds CRF with high affinity and inhibits its activity. Magnesium sulfate (MgSO₄) has been known to ameliorate maternal, fetal and gestational tissue-associated inflammatory response. We aimed to study the effect of MgSO₄ on the CRF and CRF-BP mRNA expression levels in perfused human cotyledon.

Methods: Placentas from elective caesarean section were obtained and selected cotyledons were cannulated and dually perfused ex-vivo within 30?min. MgSO₄ (7?mg/dl) was added to the maternal reservoir. Each perfusion experiment was conducted for 180?min. At the end of the experiment, RNA was extracted from the perfused cotyledon, and RT-PCR was performed to quantify the expression of CRF and CRF-BP. Human HPRT gene served as a reference gene.

Results: Perfusion with MgSO₄ (n?=?3) induced a significantly lower CRF and higher CRF-BP mRNA expression compared to placentas perfused only with medium (n?=?3).

Conclusion: In the human placenta, MgSO₄ possibly exerts its action through different modulation on the CRF and CRF-BP expression.     

Hypoperfusion causes increased production of interleukin 6 and tumor necrosis factor alpha in the isolated, dually perfused placental cotyledon

OBJECTIVE: Our purpose was to determine whether exposure of the isolated, perfused human placental cotyledon to different fetal circuit perfusion rates, and to concomitant pressure differences, alters placental production of interleukin 6 and tumor necrosis factor alpha. STUDY DESIGN: The maternal and fetal circulations of 2 cotyledons from 5 placentas were perfused for 4 hours. The fetal circulation of 1 cotyledon was perfused at a low rate of 1 mL/min, and the other at a high rate of 10 mL/min. The maternal circulation of each cotyledon was perfused at 10 mL/min. Effluents from the fetal circulation were collected at hourly intervals, and concentrations of interleukin 6 and tumor necrosis factor alpha were determined by enzyme-linked immunosorbent assay. Concentrations of interleukin 6, obtained from a prior study with an estimated physiologic fetal circulation rate of 4 mL/min, were compared with the low and high perfusion rate results. RESULTS: Concentrations of interleukin 6 and tumor necrosis factor alpha were greater at the perfusion rate of 1 mL/min, in comparison with the perfusion rate of 10 mL/min, with statistically significant differences achieved at 2 and 4 hours for interleukin 6 and at 4 hours for tumor necrosis factor alpha. Concentrations of both cytokines increased exponentially with time. Placental perfusion pressures were significantly greater at the perfusion rate of 10 mL/min. CONCLUSION: Placental hypoperfusion results in an increased production of both interleukin 6 and tumor necrosis factor alpha. This finding links placental perfusion abnormalities to the myriad of disorders associated with elevated concentrations of inflammatory cytokines, including cerebral palsy.     

Determination of metformin transfer across the human placenta using a dually perfused ex vivo placental cotyledon model

OBJECTIVE: The aim of the study was to quantify and characterize metformin transfer across the human placenta using an ex vivo placental perfusion model. STUDY DESIGN: Placentas were obtained from vaginal deliveries or caesarean sections and selected cotyledons were cannulated and dually perfused. Metformin (1 microg/ml) and a permeability reference marker, antipyrine (50 microg/ml), were added to the maternal circulation. Each perfusion experiment was conducted for 180 min while samples were taken from the maternal and fetal compartments. The integrity and viability of the placenta were determined by measuring the flow rates, fetal artery inflow pressure, and hCG production during the experiments. RESULTS: Six complete experimental set-ups were completed. The maternal-fetal transport rates for metformin and antipyrine were 10.61+/-2.85% and 30.98+/-5.62%, respectively. The clearance index, calculated as the ratio between the permeabilities of metformin and antipyrine, was 0.34+/-0.05. CONCLUSION: The results indicate that metformin is able to cross the mature human placenta; thus, fetal exposure must be considered when treating pregnant women with metformin.     

Trimethoprim and sulfamethoxazole transfer in the in vitro perfused human cotyledon

Utilizing the in vitro human placental model, we studied the placental transfer of trimethoprim and sulfamethoxazole. At trimethoprim concentrations of 7.2 micrograms/ml, only 1.4 micrograms/ml was transported across the placenta after 1 h, and at concentrations of 1.0 microgram/ml, one half the usual serum level, only 0.08 microgram/ml was transported across the placenta. Maternal concentrations of sulfamethoxazole of 29.6 and 127.7 micrograms/ml resulted in concentrations of 5.1 and 14.8 micrograms/ml on the fetal side, respectively. Thus, it would appear that trimethoprim is slowly transported across the placenta and in low concentrations whereas sulfamethoxazole readily crosses the placenta. The combination of these drugs is useful for treatment of bacteriuria. It may also prove to be especially useful for Pneumocystis carinii infections in pregnant women with AIDS. With a half-life of 13 h for trimethoprim and 6 h for sulfamethoxazole, the drugs are not likely to achieve toxic levels in the fetal compartment. Thus, it would appear that trimethoprim and sulfamethoxazole may be both efficacious and safe for the treatment of both these infections during pregnancy.     

Determination of metformin transfer across the human placenta using a dually perfused ex vivo placental cotyledon model

Objective

The aim of the study was to quantify and characterize metformin transfer across the human placenta using an ex vivo placental perfusion model.

Study design

Placentas were obtained from vaginal deliveries or caesarean sections and selected cotyledons were cannulated and dually perfused. Metformin (1 μg/ml) and a permeability reference marker, antipyrine (50 μg/ml), were added to the maternal circulation. Each perfusion experiment was conducted for 180 min while samples were taken from the maternal and fetal compartments. The integrity and viability of the placenta were determined by measuring the flow rates, fetal artery inflow pressure, and hCG production during the experiments.

Results

Six complete experimental set-ups were completed. The maternal–fetal transport rates for metformin and antipyrine were 10.61 ± 2.85% and 30.98 ± 5.62%, respectively. The clearance index, calculated as the ratio between the permeabilities of metformin and antipyrine, was 0.34 ± 0.05.

Conclusion

The results indicate that metformin is able to cross the mature human placenta; thus, fetal exposure must be considered when treating pregnant women with metformin.     

Determination of pentamidine transfer in the in vitro perfused human cotyledon with high-performance liquid chromatography

Pentamidine is used to treat Pneumocystis carinii pneumonia. The incidence of this infection in pregnancy has paralleled the increasing incidence of acquired immunodeficiency syndrome in pregnancy. Using the in vitro bidirectionally perfused human placenta, we studied the transfer of pentamidine across the placenta. Pentamidine was added to the maternal circulation at therapeutic concentrations (2 micrograms/ml). No transfer of pentamidine was detectable with a newly devised high-performance liquid chromatography method sensitive to 0.05 micrograms/ml of pentamidine. Increasing the pentamidine concentration tenfold produced a low level of transfer to the fetal circuit. Fetal concentrations were far below maternal perfusate concentrations. Placental tissue levels were higher than media levels. These data are suggestive of minimal drug transfer to the fetus and significant concentration of the drug in placental tissue.