Human umbilical vessels: responses to agents frequently used in obstetric patients

Fetal sex and the relative reactivity of human umbilical vein and arteries are key determinants in potential beneficial effects of phosphodiesterase inhibitors

Intrauterine growth restriction (IUGR) is a common complication of pregnancy. We previously demonstrated that IUGR is associated with an impaired nitric oxide (NO)-induced relaxation in the human umbilical vein (HUV) of growth-restricted females compared to appropriate for gestational age (AGA) newborns. We found that phosphodiesterase (PDE) inhibition improved NO-induced relaxation in HUV, suggesting that PDEs could represent promising targets for therapeutic intervention. This study aimed to investigate the effects of PDE inhibition on human umbilical arteries (HUAs) compared to HUV. Umbilical vessels were collected in IUGR and AGA term newborns. NO-induced relaxation was studied using isolated vessel tension experiments in the presence or absence of the nonspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX). PDE1B, PDE1C, PDE3A, PDE4B, and PDE5A were investigated by Western blot. NO-induced vasodilation was similar between IUGR and AGA HUAs. In HUAs precontracted with serotonin, IBMX enhanced NO-induced relaxation only in IUGR females, whereas in HUV IBMX increased NO-induced relaxation in all groups except IUGR males. In umbilical vessels preconstricted with the thromboxane A2 analog U46619, IBMX improved NO-induced relaxation in all groups to a greater extent in HUV than HUAs. However, the PDE protein content was higher in HUAs than HUV in all study groups. Therefore, the effects of PDE inhibition depend on the presence of IUGR, fetal sex, vessel type, and vasoconstrictors implicated. Despite a higher PDE protein content, HUAs are less sensitive to IBMX than HUV, which could lead to adverse effects of PDE inhibition in vivo by impairment of the fetoplacental hemodynamics.NEW & NOTEWORTHY The effects of phosphodiesterase inhibition on the umbilical circulation depend on the presence of intrauterine growth restriction, the fetal sex, vessel type, and vasoconstrictors implicated. The human umbilical vascular tone regulation is complex and depends on the amount and activity of specific proteins but also probably on the subcellular organization mediating protein interactions. Therefore, therapeutic interventions using phosphodiesterase inhibitors to improve the placental-fetal circulation should consider fetal sex and both umbilical vein and artery reactivity.

Functional and Histological Changes in Umbilical Artery and Myometrium Isolated from IUGR Complicated Pregnancies

Objective: To investigate the relaxation responses mediated by L-type Ca2+ channels and big-conductance Ca2+-activated K+ (BKCa) channels and histological changes in the human umbilical artery (HUA) and myometrium smooth muscle isolated from pregnancies complicated with intrauterine growth restriction (IUGR).Methods: The muscle reactivity and the histology of the smooth muscle of the HUA and myometrium retrieved from 14 women with IUGR and 14 controls were investigated by the isolated tissue bath and immunohistochemical method.Results: In HUA, the maximum relaxation responses and pD2 values of nifedipine and NS11021 (BKCa channel opener) were significantly increased and significant histopathological changes are observed in the IUGR group.Conclusions: The pathogenesis of IUGR might be associated with the impairment in the functional responses of L-type Ca2+ channels and BKCa channels in HUA smooth muscle. The increased staining of myometrium and UC with HIF-1α in IUGR may indicate apoptosis, histological damage, and impaired fetal growth.

Vasorelaxant effect of (E,E)-farnesol in human umbilical vein ex vivo assays

(E,E)-farnesol is a sesquiterpene acyclic alcohol produced by bacteria, protozoa, fungi, plants, and animals. The literature describes its applications in food, pharmaceutical, and cosmetic industries, and also in the pharmacological context with a vasorelaxant effect. However, its effects on human umbilical vessels remain poorly investigated. Thus, this study aims to investigate, in a new way, the vasorelaxant effect of (E,E)-farnesol in human umbilical veins (HUV) from healthy donors. Rings obtained from isolated HUV were suspended in an organ bath to record their isometric tension in different experimental sections. (E,E)-farnesol (1 μmol/L to 1 mmol/L) promoted vasorelaxant effect in venous preparations contracted by depolarization (KCl 60 mmol/L) or pharmacological agonism (5-HT 10 μmol/L), with EC50 values of 239.9 μmol/L and 424 μmol/L, respectively. In calcium-free solution, this effect was also observable. (E,E)-farnesol was able to suppress contractions evoked by CaCl2 and BaCl2 suggesting a blockade of voltage-dependent (especially L-type) calcium channels. The vasorelaxant efficacy and potency of (E,E)-farnesol were affected in the presence of tetraethylammonium (1 and 10 mmol/L), glibenclamide (10 μmol/L) and BaCl2 (1 mmol/L) indicating a possible involvement of potassium channels (BKCa, KATP and KIR) in this effect. Our data suggest that (E,E)-farnesol has a promising potential to be applicable as a vasodilator in hypertensive conditions in pregnancy that alter HUV reactivity.

In vitro fertilization with frozen embryo transfer increased histamine-mediated contractile sensitivity via PKCβ in human umbilical vein

OBJECTIVE

In vitro fertilization-embryo transfer (IVF-ET) technologies (especially frozen ET) have been widely used, which might affect maternal and fetal health. Information regarding influence of IVF-ET on the vasoconstriction of human umbilical vein (HUV) is limited. This study determined effects of frozen ET on histamine-mediated vascular responses in HUV and related mechanisms.

METHODS AND RESULTS

HUVs were collected from frozen ET conceived pregnancy and spontaneously conceived pregnancy (control). Histamine concentration in umbilical plasma was higher in frozen ET group than the control. Histamine-mediated contractile response curve was left-shifted in the frozen ET group when comparing with the control. In isolated HUV rings, H1R showed a critical role in regulating vascular constriction, while H2R played little roles in regulating vessel tone. Iberiotoxin and 4-aminopyridine didn't significantly change histamine-mediated constriction in HUVs. Histamine-induced vasoconstrictions were significantly decreased by nifedipine, KN93, or GF109203X, while the inhibitory effects were significantly greater in the frozen ET group in comparison to the control. The constrictions by Bay K8644, phenylephrine, or PDBu were stronger in frozen ET, respectively. There was a decrease in the protein expressions of H1R and H2R, an increase in protein expressions of BK_Caα and PKCβ.

CONCLUSIONS

Histamine-induced constriction in HUV was mainly via H1R. The increased sensitivity to histamine in HUV following frozen ET cycles were linked to the enhanced PKCβ protein expression and function. The new data and findings in this study provide important insight into influences of frozen ET on fetal vessel development and potential influence in long-term.

Effects of bisphenol A on human umbilical arteries

Bisphenol A (BPA) is an endocrine-disrupting chemical widely used in the plastics industry, including food container, toys, and medical equipment. We analyzed the effect of BPA in human umbilical artery contractility and expression of some proteins modulating this function, such as ionic channels and proteins involved in the cGMP pathway. Using standard organ bath technique, rings of human umbilical arteries without endothelium were contracted by 5-HT (1 μM) and histamine (10 μM) and the effect of different concentrations of BPA (1 nM-100 μM) was analyzed. The results showed that BPA is a vasodilator of these arteries in a concentration-dependent way. Besides, qPCR studies on human umbilical smooth muscle cells (HUSMC) allowed to analyze the effects of BPA on gene expression. Thus, 12-h exposition to BPA induced reduction of expression of L-type calcium channels (LTCC), alpha subunit of BK_Ca channels, and Kvβ1 and Kvβ3 from Kv channels. BPA also decreased the expression of soluble guanylate cyclase (sGC) and natriuretic peptide receptor type A (NPRA), meanwhile increasing that of PKG, proteins involved in vasodilation of human umbilical arteries (HUA) by cGMP. Further studies will be necessary to increase knowledge about the implications of these changes induced by BPA exposure.

Comparison of relaxant effects of nifedipine and NS11021 on isolated umbilical arteries of healthy and preeclamptic pregnant women

OBJECTIVES

Potassium (K⁺) channel openers and calcium (Ca²⁺) channel blockers are currently used to treat acute severe hypertension in pregnancy. We aimed to investigate the vasorelaxant effect of NS11021, a potent and specific big-conductance Ca²⁺-activated K⁺ (BKCa) channel activator, and to compare it with the vasorelaxant effect of nifedipine on human umbilical arteries (HUAs) isolated from healthy and preeclamptic pregnants.

STUDY DESIGN

A total of 29 HUAs were isolated immediately after delivery from 14 healthy and 15 preeclamptic pregnant with severe features. The concentration-dependent relaxation responses were obtained to nifedipine and NS11021 on HUAs precontracted with endothelin-1 (ET-1) (10^-8 M) in an isolated tissue bath.

RESULTS

Both nifedipine and NS11021 caused concentration-dependent relaxation responses in HUAs from healthy and preeclamptic pregnants. While the maximum responses (Emax) and pD₂ values of nifedipine did not change significantly in both groups, the Emax and pD₂ values of NS11021 were significantly decreased in the preeclampsia group (Emax ± SEM; %75.57 ± 4.53 and %43.75 ± 14.00 and pD₂ ± SEM; 6.92 ± 0.26 and 5.24 ± 0.53 respectively, p < 0.05). In addition, the pD₂ value of NS11021 was not significantly different from that of nifedipine in the control group, but decreased significantly in the preeclampsia group (pD₂ ± SEM 7.1 ± 0.41 and 5.2 ± 0.53, p < 0.05, respectively).

CONCLUSIONS

Efficacy and potency of NS11021 decreased in HUAs from preeclamptic pregnants. Also, NS11021 is less potent than nifedipine in the preeclampsia group. BKCa channels may have a role in the pathogenesis of preeclampsia, however, further experimental studies are needed to elucidate that.

Vasorelaxant effect of monoterpene carvacrol on isolated human umbilical artery

Carvacrol is the main compound of essential oils extracted primarily from Thymus and Origanum species. Its various biological activities were confirmed: antioxidant, anti-inflammatory, antibacterial, antifungal, anti-tumour, antinematodal and vasorelaxant action. Although vasodilation mediated by carvacrol was previously described, the exact mechanism of its action has not yet been established. Hence, the aim of this study was to investigate carvacrol vasoactivity on human umbilical arteries (HUA) and different pathways involved in its mechanism of action using tissue bath methodology. Carvacrol caused a significant decrease in vascular tension of 5-HT-pre-contracted umbilical arteries, with EC50 of 442.13 ± 33.8 µM (mean ± standard error of the mean - SEM). At 300 µM, carvacrol shifted downward the 5-HT concentration-response curve with statistical significance of p < 0.001 obtained for the four highest concentrations. At concentration of 1 mM, carvacrol completely abolished BaCl2-induced contraction in Ca2+-free Krebs-Ringer bicarbonate solution (p < 0.001). Isopentenyl pyrophosphate, the antagonist of TRPV3 channel, was able to decrease the efficacy of carvacrol (p < 0.001). The vasorelaxant effect of carvacrol seems to involve the blocking of L-type of Ca2+ channels on smooth muscle cells. However, the role of TRPV3 channels in carvacrol-induced vasodilation of HUA cannot be excluded either.

Evaluation of magnesium sulfate effects on fetus development in experimentally induced surgical fetal growth restriction in rat

Objective: The objective of this study was to evaluate the effect of magnesium sulfate in the prevention of fetal growth restriction due to the impaired uterine blood supply in the rat model.Methods: A total number of 24 female rats were used in this study. They were mated overnight and randomly divided into control and treatment groups. After anesthesia and incising abdominal midline in day 17 of gestation, the uterine artery was occluded by an atraumatic clamp for 60 min. The rats of the control group received normal saline after surgery and the rats of treatment group received magnesium sulfate subcutaneously. The laparotomy was repeated on day 21 of gestation, and the number of alive and dead fetuses was counted in each horn. The viability of fetuses was evaluated. The weight of the placenta and fetuses and the distance between the head and tail as well as back to the abdomen of the fetuses were also measured. Samples of the amniotic fluid (AF) were collected during both surgeries for biochemical analyses of the glucose, urea, lactate, and pyruvate levels by an AutoAnalyzer.Results: Among the total fetuses in ischemic horn, only 50% survived in the control group. Dead fetuses had less body consistency and had a dark color. In contrary, only 7.6% of the fetuses in the treatment group were absorbed and 92.4% were completely healthy and developed. Parameters related to placenta weight, fetus weight, fetus length, and fetus width had significant differences and those of the treatment group were higher. Glucose and lactate levels of the AF in the treatment group were significantly lower and urea level was significantly higher than the control group in day 21 of gestation. The changes in pyruvate levels were not significant.Conclusion: In conclusion, magnesium sulfate may counteract with the effects of temporary uterine ischemia in pregnant rats and prevent intrauterine growth restriction.

Nifedipine increases fetoplacental perfusion

AIM

Our aim is to evaluate the effect of nifedipine on fetoplacental hemodynamic parameters.

METHODS

A retrospective study was conducted at a tertiary center with 30 patients for whom nifedipine treatment was used as a tocolytic therapy for preterm labor. Initiation of this treatment was at 31.6±2.5 weeks of gestation. We combined the pulse Doppler imaging parameters with grayscale imaging via the Bernoulli theorem, which is called the "continuity equation", to get the fetoplacental perfusion (FPP). Evaluated parameters were the resistance index (RI), the pulsatility index (PI), systole/diastole ratios (S/D), the velocity-time integral of the umbilical artery (VTI), the radius of the umbilical artery, the peak systolic velocity and the mean pressure gradient in the umbilical artery. From these parameters, the FPP was acquired.

RESULTS

We found that the RI, the PI and the S/D ratio did not change after treatment with nifedipine. The mean pressure gradient, the VTI and the peak systolic velocity increased after treatment with nifedipine. Nifedipine increases FPP from 166±73.81 beat.cm3/min to 220±83.3 beat.cm3/min.

DISCUSSION

Although nifedipine had no effect on the PI, the RI or the S/D, it increased the mean pressure gradient, the VTI and FPP.

The Effects of Bumetanide on Human Umbilical Artery Contractions

The authors investigate the effect of bumetan ide, an inhibitor of NKCC1 and a loop diuretic, on the tone of human umbilical artery (HUA). Rings of HUA (n = 35) from vaginal deliveries were suspended for isometric tension recordings in organ baths. Cumulative concentration-response curves to serotonin, histamine, and KCl were performed in the absence (control) or in the presence of bumetanide. The relaxant effect of bumetanide was also evaluated in serotonin- and histamine-induced contractions. Bumetanide inhibited HUA tone in serotonin- and histamine-induced contractions with significant changes in the potency (pD(2)) and maximum contractile response (E(max)) values. However, only pD( 2) values for KCl-induced contraction significantly changed in the presence of bumetanide. Bumetanide caused concentration-dependent and sustained relaxations in serotonin-induced contraction; however, there was refractoriness in histamine-induced contraction. These findings raise the possibility that NKCC1 may play a role in the regulation of the umbilical artery tone.

The effect of loading dose of magnesium sulfate on uterine, umbilical, and fetal middle cerebral arteries Doppler in women with severe preeclampsia: A case control study

SYNOPSIS IV MgSO4 administration in women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices.

OBJECTIVE

To evaluate Doppler parameters of the umbilical artery (UmA), uterine artery (UA), and fetal middle cerebral artery (MCA) before and after MgSO4 administration in women with severe preeclampsia.

METHODS

A case control study included 100 pregnant women with severe preeclampsia. Umbilical artery, uterine artery, and fetal middle cerebral artery Doppler were measured before and 20 minutes after intravenous administration of 6 g of magnesium sulfate.

RESULTS

There was a significant difference between maternal systolic blood pressure (173.20 ± 22.72 vs. 156.60 ± 19.18), diastolic blood pressure (109.60 ± 9.14 vs. 101.90 ± 10.05), and heart rate (80.52 ± 11.52 vs. 88.48 ± 12.08) before and after administration of MgSO4 in the studied patients (p value < 0.001). There was a significant difference between umbilical artery, middle cerebral artery, and uterine artery Doppler parameters before and after administration of MgSO4 in the studied patients (p value < 0.001). There was no significant difference between umbilical artery/middle cerebral artery with regard to RI and PI. However, there was significant difference with regard to the S/D ratio (p value < 0.001). The decrease in the values of Doppler parameters before and after administration of MgSO4 was more in the middle cerebral artery than in the umbilical artery.

CONCLUSION

Intravenous administration of magnesium sulfate in pregnant women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices with reduced resistance to blood flow in these vessels.

Effect of the loading dose of magnesium sulfate (MgSO4) on the parameters of Doppler flow velocity in the uterine, umbilical and middle cerebral arteries in severe preeclampsia

OBJECTIVE

To evaluate Doppler velocimetry parameters (resistance index [RI], pulsatility index [PI] and systolic/diastolic [S/D] ratio) of maternal-fetal circulation before and after magnesium sulfate administration in pregnant women with severe preeclampsia.

METHODS

A prospective observational cohort analysis of 40 women with severe preeclampsia was performed. Doppler ultrasonography scans were performed before and 20 minutes after intravenous administration of magnesium sulfate. Maternal parameters such as heart rate, and systolic, diastolic and mean arterial pressure were recorded. Doppler flow velocity parameters (RI, PI and S/D ratio) were evaluated in the uterine, umbilical and middle cerebral arteries. The different mean values obtained before and after magnesium sulphate were analyzed using the paired t-test.

RESULTS

There was a statistically significant increase in mean maternal heart rate and a statistically significant decrease in systolic, diastolic and mean maternal blood pressure before and after administration of magnesium sulphate (p < 0.001). Resistance index decreased in the umbilical (p = 0.003; 95% CI: 0.008 - 0.03) and middle cerebral artery (p = 0.001; 95% CI: 0.01 - 0.05) and in both uterine arteries. Likewise, there was a significant reduction in the PI and S/D ratio in all the arteries assessed.

CONCLUSIONS

Maternal administration of intravenous magnesium sulfate in preeclampsia leads to an increase in maternal heart rate and a decrease in systolic, diastolic and mean arterial blood pressure. A reduction in the resistance index, pulsatility index and S/D ratio was recorded in the uterine, umbilical and cerebral arteries.

Efficacy of different vasodilators on human umbilical arterial smooth muscle under normal and reduced oxygen conditions

The ability of the smooth muscle of the human umbilical artery to relax may vary under physiological and pathological conditions. We investigated the responsiveness of that preparation to relaxation, as well as the influence of reduced oxygen condition on these responses. Rings of human umbilical arteries from full-term Caesarian deliveries were suspended in modified Krebs-Henseleit solutions bubbled with a gas mixture of 95% O2:5% CO2 (normal oxygen condition) or 2.5% O2:8% CO2 balanced with N2 (reduced oxygen condition). These rings were contracted with potassium chloride, serotonin or the thromboxane A2 mimetic U46619, before being exposed to either the nitrovasodilator sodium nitroprusside, the potassium channel opener levcromakalim or the calcium channel antagonist amlodipine. While sodium nitroprusside elicited relaxation in this blood vessel, the maximal relaxation to the nitric oxide donor was significantly smaller than that induced by levcromakalim and amlodipine. The nature of the constrictor agent used, or changes of oxygen conditions did not significantly affect the relaxation profile of this human blood vessel. These data suggest that the smooth muscle of the human umbilical artery may be less responsive to vasodilators that act via the nitric oxide pathway. Moreover, vascular responses of umbilical arterial smooth muscle to relaxing agents do not alter under hypoxic or different vasoconstricting conditions.

Anti-hypertensive therapy and the feto-placental circulation: effects on umbilical artery resistance

OBJECTIVE

To investigate and compare the direct effects of compounds used in the treatment of hypertensive disease in pregnancy on human umbilical artery resistance in vitro.

METHODS

Isometric tension recordings were performed under physiological conditions on human umbilical arterial rings (n=30). The in vitro effects of labetolol, hydralazine, alpha-methyldopa, nifedepine and magnesium sulphate (at concentration ranges from 1 nanomolar to 1 millimolar), and their respective vehicle controls, were measured. Results were expressed as -logEC50 (pD2) and mean maximal inhibition values for each compound.

RESULTS

All compounds investigated, except alpha methyldopa, exerted a significant relaxant effect on umbilical arterial tone. Alpha-methyldopa was significantly less potent when compared to all other compounds (mean maximal inhibition value [20.89+/-7.99%] versus all other agents [range 63.15+/-8.70-84.12+/-3.84%] (P<0.01)). The dose response curve of nifedipine yielded a significantly greater PD2 value when compared to that of hydralazine, labetalol, and magnesium sulphate (PD2 value [5.82+/-0.34] versus the above groups [range 3.10+/-0.09-3.52+/-0.14] (P <0.01)).

CONCLUSION

These findings demonstrate that agents commonly used for the treatment of hypertensive disease in pregnancy, excluding alpha-methyldopa, have significant direct effects on the feto-placental circulation. These results suggest that alpha-methyldopa administration during pregnancy is less likely to produce significant direct effects on fetal vasculature then other agents used.

Magnesium-induced vasodilation in the dorsal hand vein

OBJECTIVE

Magnesium affects blood pressure by modulating vascular tone and reactivity. In obstetric patients, magnesium is administered to prevent eclamptic seizures and as a tocolytic to treat preterm labour. Prior to studying vascular sensitivity in women with pre-eclampsia, we sought to determine the effect of magnesium on venous tone in healthy women of childbearing age.

DESIGN

Dose-response study.

SETTING

Columbia-Presbyterian Medical Center, New York.

POPULATION

Ten healthy non-pregnant women (age range 21-47 years).

METHODS

Vascular response to magnesium sulphate (MgSO4) was measured in a dorsal hand vein using the linear variable differential transformer (LVDT) technique. Complete dose-response curves to MgSO4 (0.0000275-0.088 mmol/min) were determined after 50% preconstriction of the vein with phenylephrine.

MAIN OUTCOME MEASURES

The ED50 of MgSO4 (dose resulting in 50% of maximal effect, Emax) was determined. Blood samples from the contralateral upper extremity were obtained to assess total plasma magnesium levels at baseline and at the highest infused dose of magnesium. ED50 results are expressed as geometric mean (95% confidence interval, CI). Emax results and magnesium plasma concentrations are expressed as mean [SD].

RESULTS

The ED50 of MgSO4 was 0.000307 mmol/min (95% CI 0.138, 0.666) and Emax was 102% [20%].

CONCLUSION

Magnesium induces dose-dependent venodilation in healthy women in the absence of systemic haemodynamic effects. The dose resulting in vasodilation using the LVDT/hand vein model is two to three orders of magnitude less than the therapeutic doses of magnesium used for tocolysis or seizure prophylaxis. Studies of the effect of systemically administered therapeutic doses of magnesium on vascular reactivity in pre-eclampsia will be of interest.

Involvement of calcitonin gene-related peptide in control of human fetoplacental vascular tone

Calcitonin gene-related peptide (CGRP), one of the most potent endogenous vasodilators known, has been implicated in vascular adaptations and placental functions during pregnancy. The present study was designed to examine the existence of CGRP-A receptor components, the calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1), in the human placenta and the vasoactivity of CGRP in the fetoplacental circulation. Immunofluorescent staining of the human placenta in term labor using polyclonal anti-CRLR and RAMP1 antibodies revealed that labeling specifically concentrated in the vascular endothelium and the underlying smooth muscle cells in the umbilical artery/vein, chorionic artery/vein, and stem villous vessels as well as in the trophoblast layer of the placental villi. In vitro isometric force measurement showed that CGRP dose dependently relaxes the umbilical artery/vein, chorionic artery/vein, and stem villous vessels. Furthermore, CGRP-induced relaxation of placental vessels are inhibited by a CGRP receptor antagonist (CGRP8–37), ATP-sensitive potassium (KATP) channel blocker (glybenclamide), and cAMP-dependent protein kinase A inhibitor (Rp-cAMPS) and partially inhibited by a nitric oxide inhibitor ( Nω-nitro-l-arginine methyl ester). We propose that CGRP may play a role in the control of human fetoplacental vascular tone, and the vascular dilations in response to CGRP may involve activation of KATP channels, cAMP, and a nitric oxide pathway.

The vasodilatory effects of hydralazine, nicardipine, nitroglycerin, and fenoldopam in the human umbilical artery

We studied the effects of hydralazine, nicardipine, nitroglycerin, and fenoldopam (a dopamine D1-agonist) on isolated human umbilical arteries (HUA) from patients classified as normotensive and with pregnancy-induced hypertension (PIH). Umbilical artery rings were contracted with the thromboxane A(2) analog (U46619; 10(-8) M) and then exposed to cumulative concentrations of fenoldopam, hydralazine, nicardipine, and nitroglycerin. Second, rings were preexposed to prazosin (10(-5) M), phenoxybenzamine (10(-5) M), or none, and the constriction responses to increasing doses of fenoldopam or dopamine were recorded. Nitroglycerin, hydralazine, and nicardipine produced concentration-dependent relaxation of U46619-preconstricted HUA segments from normotensive and PIH patients. Fenoldopam and dopamine induced umbilical artery constriction in both normal and PIH rings at concentrations > or = 10(-5) M and > or = 10(-3) M, respectively. Phenoxybenzamine, but not prazosin, pretreatment irreversibly abolished fenoldopam-induced contraction. In this in vitro study, nitroglycerin was the most potent vasodilator of the HUA constricted with U46619, followed by nicardipine and hydralazine. However, fenoldopam constricted HUA rings only at supratherapeutic concentrations. No significant differences of vascular responses to fenoldopam (P = 0.3534), nitroglycerin (P = 0.7416), nicardipine (P = 0.0615), and hydralazine (P = 0.5514) between rings from normotensive or hypertensive pregnant patients were shown.

Influence of magnesium sulphate and isradipine on human placental cotyledon fetal vessels in vitro

Increased systemic vascular resistance and blood pressure during pregnancy may be due to impaired prostacycline PGI(2)-thromboxan (TX) A(2) balance. The aim of the study was to compare the influence of magnesium sulphate and isradipine on the placental vascular resistance induced by stable thromboxan A(2) analogue U 46619 in experimental bilateral perfusion of the human placental cotyledon. The research used the experimental model described by Schneider et al. [Am. J. Obstet. Gynecol. 114 (1972) 822]. The control group consisted of six placental lobule perfusions lasting 120 min each. Constant increase in perfusion pressure of mean value 185% of the initial pressure was obtained from about the 60th min of the experiment and maintained till the end. Having obtained constant increase in perfusion pressure from the 60th min of the experiment, magnesium sulphate and isradipine were administered along with thromboxan A(2) analogue U 46619 into the fetal circulation. Both drugs lowered perfusion pressure, experimentally increased by thromboxan A(2) analogue U 46619. The onset of magnesium sulphate activity was quicker than isradipine. According to the results of our in vitro study, magnesium sulphate and isradipine may have a beneficial effect on vascular resistance of cotyledon vessels in PIH in vivo, too.

Isolated human chorionic vascular reactivity: technical considerations for fresh preparations

1. Sixty chorionic vascular rings from normal term placentas were immersed in an organ bath for isometric tension recording to study (A) the contractile response to 120 mM of potassium chloride (KCl) after adjustment and equilibration to 1-5 g of passive tension; and (B) the concentration-response curve to KCl after adjustment and equilibration to the optimal passive tension. 2. Adjustment to 4 g of passive tension elicited the maximal (P < 0.007) and the latest (P < 0.006) KCl-induced contraction among arterial rings. Venous rings showed the greatest contraction when adjusted to 3 g, but the differences were not significant except when compared to 1 g of passive tension (P < 0.03). 3. The EC50 for chorionic arteries and veins was 14.2 and 25.7 mM, respectively (P < 0.003). The maximal contraction was already obtained with 40 mM of KCl. 4. Our results suggest that (A) the optimal passive tension for fresh human chorionic arteries is 4 g; (B) chorionic venous reactivity is less influenced by the initial tension; and (C) the optimal concentration of KCl to be used as a contracting agent of these tissues is 40 mM.

Magnesium sulfate attenuates peroxide-induced vasoconstriction in the human placenta

OBJECTIVE

Magnesium sulfate is used to prevent convulsions in preeclamptic women. It acts as a calcium antagonist but may also stimulate prostacyclin. Because magnesium sulfate readily crosses the placenta, we evaluated whether it might have a beneficial effect on placental blood flow.

STUDY DESIGN

Isolated human placental cotyledons (n = 6) were perfused for 20-minute intervals with control Krebs-Ringer-bicarbonate buffer, 200 mumol/L t-butyl hydroperoxide, magnesium sulfate (6 mEq/L), peroxide plus magnesium sulfate, and peroxide plus magnesium sulfate plus calcium chloride (6.25 mEq/L). Peroxide perfusion was used to stimulate thromboxane to induce vasoconstriction. Fetal perfusion pressure was continually monitored. Maternal and fetal effluent samples were analyzed for thromboxane and prostacyclin by their stable metabolites, thromboxane B2 and 6-keto-prostaglandin F1 alpha.

RESULTS

Compared with control Krebs-Ringer-bicarbonate buffer perfusion, peroxide perfusion significantly increased (p < 0.05) vascular resistance (12.9 +/- 1.2 vs 21.1 +/- 2.6 mm Hg.min/ml, mean +/- SE) and thromboxane B2 secretion (fetal -0.22 +/- 0.08 vs 0.73 +/- 0.11 ng/min, maternal -1.5 +/- 0.4 vs 4.4 +/- 0.7 ng/min). Subsequent perfusion with magnesium sulfate significantly attenuated (p < 0.05) peroxide-induced vasoconstriction (15.1 +/- 1.7 mm Hg.min/ml), which was reversed by the addition of calcium (19.7 +/- 2.2 mm Hg.min/ml). Magnesium sulfate partially, but significantly (p < 0.05), inhibited the peroxide-induced increase in maternal thromboxane B2 secretion (3.2 +/- 0.6 ng/min) but not fetal thromboxane B2 secretion (1.1 +/- 0.3 ng/min). Magnesium sulfate did not affect 6-keto-prostaglandin F1 alpha secretion.

CONCLUSIONS

(1) Magnesium sulfate attenuates peroxide-induced vasoconstriction in the human placenta. (2) This effect is mediated by inhibition of thromboxane synthesis and antagonism of calcium.

Drug-induced vasodilation in an in vitro and in vivo study: the effects of nicardipine, papaverine, and lidocaine on the rabbit carotid artery

Extreme arterial vasoconstriction (vasospasm) is a common problem encountered in microvascular surgery. An ideal pharmacologic tool able to counteract ischemia during microsurgery should be easy to apply and exert its action both locally and distally in the microcirculation of the flap. We have compared in vitro and in vivo vascular properties of nicardipine, papaverine, and lidocaine in the rabbit carotid artery. In vitro, rings from the rabbit carotid artery (n = 7) were bathed in Krebs-Ringers solution and stretched progressively to an optimal tension of 3.7 to 4.2 g. The specimens were contracted with norepinephrine (1 microM), and a cumulative dose response curve was established. In vivo, microvascular anastomoses were performed bilaterally in the rabbit carotid artery in 35 animals using 9-0 nylon suture and standard microsurgical techniques. During and after the anastomoses, nicardipine (0.1, 0.01 mg topical, or 0.1 mg/hour IV), papaverine (30 mg/cc topical), and lidocaine (2% with and without epinephrine) were applied (blinded) at the anastomotic site in five rabbits each. Heparinized sodium chloride was used as topical irrigation for control and to clean the anastomosis. Blood flow changes were monitored continuously with the transonic Doppler for 30 minutes after the procedure. The systemic blood pressure was also monitored in a group of pilot experiments. A documented decrease in blood flow was noted in all animals after the microvascular anastomosis. Nicardipine and papaverine evoked a concentration-dependent relaxation to precontracted rings to norepinephrine. Nicardipine was greater than papaverine in inducing relaxation. Lidocaine demonstrated a biphasic response with low concentrations potentiating contraction. Systemic nicardipine and papaverine significantly increased the blood flow in the rabbit carotid artery. Topical application of nicardipine and lidocaine did not significantly alter the blood flow; however, the application of nicardipine demonstrates a trend toward increased flow. Lidocaine with epinephrine significantly decreased the blood flow. No drug was found to alter the blood pressure of the animals. Our results demonstrate that nicardipine and papaverine seem to be pharmacologic tools able to increase the blood flow in anastomotic arteries. In contrast, the use of 2% lidocaine as a spasmolytic agent should be re-evaluated, since this substance may act as a partial agonist.