Effect of the vascular endothelium on norepinephrine-induced contractions in uterine radial arteries from the nonpregnant and pregnant human uterus

Dystocic Labor and Adrenergic and Noradrenergic Neurotransmitters: A Morphological Experimental Study

Authors investigated the catecholaminergic neurotransmitters (chNs) quantitative modifications in pregnant uterine Lower Uterine Segment (LUS) during prolonged labor (PL) with the fetus in an occiput-posterior position (OPP), in occiput transverse position (OTP) and in fetal head asynclitism, all diagnosed by Intrapartum Ultrasonography (IU). The chNs neurotransmitters, particularly adrenaline (or epinephrine-A) and noradrenaline (or norepinephrine-N), were evaluated in LUS fragments sampled during CS of 34 patients undergoing urgent cesarean section (CS) in PL, compared to chNs fibers in the LUS of 36 women submitted to elective CS. All results were statistically analyzed to understand the differences in neurotransmitters morphological analysis by scanning electronic microscopy examination (SEM). The LUS fragments analysis revealed a reduction of A and N fibers in LUS during PL, compared with the expression of A and N fibers in LUS during elective CS. The PL for OPP, the OTP and asynclitism, all positions causing dystocia in labor lead to a reduction in neurotransmitters in LUS, with a uterine vascularization modification and a reduction in the contractility of smooth uterine cells. The A and N neurotransmitters reduction observed in PL negatively interferes with uterine contraction during labor.

Antidepressant use and risk for preeclampsia

BACKGROUND

Prior studies suggest that women who use antidepressants during pregnancy have an increased risk for preeclampsia, yet the comparative safety of specific antidepressants remains unclear. US nationwide Medicaid Analytic eXtract (MAX) data have not been used to study medication safety during pregnancy.

METHODS

We identified 100,942 pregnant women with depression from 2000 to 2007 MAX data. We used pharmacy dispensing records to ascertain exposure to selective serotonin reuptake inhibitor (SSRI), serotonin-norepenephrine reuptake inhibitor (SNRI), tricyclic, bupropion, other antidepressant monotherapy or polytherapy, and specific antidepressants, during the second trimester and first half of the third trimester. Relative risks (RRs) and 95% confidence intervals (CIs) were adjusted for delivery year, preeclampsia risk factors, depression severity proxies, other antidepressant indications, other medications, and healthcare utilization.

RESULTS

The risk of preeclampsia was 5.4% among women with depression and no antidepressant exposure. Compared with these women, the risk for preeclampsia was higher among those receiving SNRI (RR: 1.52, 95% CI = 1.26-1.83) and tricyclic monotherapy (RR: 1.62, 95% CI = 1.23-2.12), but not SSRI monotherapy (RR: 1.00, 95% CI = 0.93-1.07) or other antidepressants. Compared with women receiving SSRI monotherapy, preeclampsia risk was higher among women with SNRI (RR: 1.54, 95% CI = 1.28-1.86) and tricyclic (RR: 1.64, 95% CI = 1.25-2.16) monotherapy. None of the specific SSRIs was associated with preeclampsia. The RR with venlafaxine was 1.57 (95% CI = 1.29-1.91) and with amitriptyline 1.72 (95% CI = 1.24-2.40).

CONCLUSIONS

In this population, SNRIs and tricyclics were associated with a higher risk of preeclampsia than SSRIs.

Large conductance Ca2+-activated K+ channels modulate uterine α1-adrenergic sensitivity in ovine pregnancy

The uteroplacental vasculature is refractory to α-adrenergic stimulation, and large conductance Ca(2+)-activated K(+) channels (BK(Ca)) may contribute. We examined the effects of uterine artery (UA) BK(Ca) inhibition with tetraethylammonium (TEA) on hemodynamic responses to phenylephrine (PE) at 101 to 117 days and 135 to 147 days of ovine gestation, obtaining dose responses for mean arterial pressure (MAP), heart rate (HR), and uteroplacental blood flow (UPBF) and vascular resistance (UPVR) before and during UA TEA infusions. The UA α(1)-adrenergic receptors (α1-ARs) were assessed. The PE increased MAP and UPVR and decreased HR and UPBF dose dependently at both gestations (P < .001, analysis of variance). The %▵MAP was less at 135 to 147 days before and during TEA infusions (P ≤ .008); however, responses during TEA were greater (P ≤ .002). The PE increased %▵UPVR>>%▵MAP, thus %▵UPBF fell. The TEA enhanced PE-mediated increases in %▵UPVR at 135 to 147 days (P ≤ .03). The UA α(1)-AR expression was unchanged in pregnancy. Uterine vascular responses to PE exceed systemic vascular responses throughout pregnancy and are attenuated by BK(Ca) activation, suggesting BK(Ca) protect UPBF.

The role of nitric oxide in female reproduction

The cardiovascular system undergoes profound changes during pregnancy. Maternal intravascular volume begins to increase in the first trimester rising an average of 45% by term.1Cardiac output increases similarly2and is redistributed to organs whose functions are crucial for a successful pregnancy. In the guinea pig, uterine artery (UA) blood flow increases 3500%, while mesenteric and renal artery blood flows increase only 90% and 10% respectively.3Blood flow to the trunk actually diminishes. The mechanism underlying this redistribution is unknown. Coupled with the rise in cardiac output is a decrease in the systemic pressor response to angiotensin II (AII), norepinephrine(NE), and epinephrine.4–8There is also a decrease in the contraction response among some but not all vascular beds. For example, contraction of UA to NE and thromboxane is characteristically reduced by pregnancy, whereas the response of the carotid artery is unaltered8–10Since pregnancy does not alter neuroeffector mechanisms of NE such as release, receptor sensitivity, and accumulation11, changes in sympathetic control during pregnancy must be dependent on alterations at sites other than the neuroeffector junction. We have hypothesized that the mechanisms which alter vascular reactivity during pregnancy also mediate the redistribution of maternal cardiac output.9We have further hypothesized that many of these mechanisms involve endothelium-dependent factors which are modulated by sex hormones.

Contribution of coupling between human myometrial beta2-adrenoreceptor and the BK(Ca) channel to uterine quiescence

The beta(2)-adrenergic receptor (beta(2)-AR) and the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel have been shown, separately, to be involved in mediating uterine relaxation. Our recent studies reveal that the levels of both beta(2)-AR and BK(Ca) channel proteins in pregnant human myometrium decrease by approximately 50% after the onset of labor. We present direct evidence in support of a structural and functional association between the beta(2)-AR and the BK(Ca) channel in pregnant human myometrium. Localization of both proteins is predominantly plasmalemmal, with 60% of beta(2)-AR colocalizing with the BK(Ca) channel. Coimmunoprecipitation studies indicate that BK(Ca) and beta(2)-AR are structurally linked by direct protein-protein interactions. Functional correlation was confirmed by experiments of human myometrial contractility in which the BK(Ca) channel blocker, paxilline, significantly antagonized the relaxant effect of the beta(2)-AR agonist ritodrine. These novel findings provide an insight into the coupling between the beta(2)-AR and BK(Ca) channel and may have utility in the application of this signaling cascade for therapeutic potential in the management of preterm labor.

Noradrenaline-induced vasoconstriction in the uterine vascular bed of pregnant rats chronically treated with L-NAME: role of prostanoids

Vascular reactivity to vasoconstrictors has been observed in preeclamptic vessels. In this investigation, the possible role of endothelin-1 and endoperoxide/thromboxane receptor activation in the exaggerated response of the uterine vascular bed from rats with experimentally induced preeclampsia-like syndrome to noradrenaline was studied. The mean blood pressure in non-pregnant rats was 126.0 +/- 8.7 mm Hg (n = 5) while in pregnant rats, the mean blood pressure was 110.0 +/- 4.7 mm Hg (n = 5). Corresponding values in l-NAME-treated non-pregnant and pregnant rats were 167.5 +/- 6.9 mm Hg (n = 6) and 167.5 +/- 6.9 mm Hg (n = 6). These values were not significantly (P > 0.05) different from each other but were significantly (P < 0.05) different from corresponding values in control rats (not treated with l-NAME). Noradrenaline (10-10-10-6 mol) produced potent and reproducible vasoconstriction in isolated perfused rat uterine vascular bed from l-NAME-treated and untreated pregnant and non-pregnant rats. There was no significant difference in the potency of noradrenaline. However, there was an increase in the absolute maximum response to noradrenaline in uterine vascular bed from l-NAME-treated pregnant rats when compared with the other groups. Noradrenaline-induced vasoconstriction was not significantly affected by AT1-receptor antagonist, ZD 7155 or SB 209670, a potent ETA/ETB receptor antagonist. Vasoconstrictor responses to noradrenaline were however significantly reduced by indomethacin and SQ 29548 in l-NAME-treated pregnant rats. These observations would suggest that in pregnant rats treated with l-NAME, cyclooxygenase products play a significant role in noradrenaline-induced vasoconstriction of this preparation.

Insulin-mediated vasorelaxation in pregnancy

OBJECTIVE

To investigate insulin-mediated vasorelaxation in pregnancy, and the role of nitric oxide in this response.

DESIGN

In vitro study of isolated subcutaneous resistance arteries from pregnant and non-pregnant women.

METHODS

Small arteries (mean vessel diameter <300 microm) were isolated from biopsies of subcutaneous fat from 14 pregnant and seven non-pregnant women. Insulin-mediated attenuation of the vasoconstriction response to noradrenaline, before and after nitric oxide synthase inhibition, was studied in isolated arteries using wire myography. Vessel responses to noradrenaline following incubation with insulin were also tested after endothelial denudation. Maximum responses were compared using one-way ANOVA and Bonferroni's post hoc test for multiple comparisons.

RESULTS

In pregnancy, the maximum vasoconstriction produced by noradrenaline was increased (P < 0.01). Insulin significantly reduced this response in pregnant women (P < 0.01), while inhibition of nitric oxide synthase with Nomega-nitro-L-arginine methyl ester (L-NAME) resulted in potentiation (P < 0.05). Following inhibition of nitric oxide synthase with L-NAME, addition of the insulin was still able to produce a significant attenuation in maximum vasoconstriction to noradrenaline in pregnant women (P < 0.01). Furthermore, the absence of functioning endothelium did not abolish the attenuating effect of the insulin on noradrenaline-induced vasoconstriction in pregnant women (P < 0.01).

CONCLUSIONS

The vasodilatory effect of insulin is not diminished in pregnancy, despite the development of insulin resistance. Furthermore, the attenuation of vasoconstrictor tone is via an endothelium-independent mechanism. This suggests that the vascular dysfunction associated with diabetes mellitus does not occur with physiological insulin resistance.

In vivo regulation of vasomotricity by nitric oxide and prostanoids during gestation

Pharmacological studies using the Doppler technique revealed that pregnancy decreases the systemic blood pressure and enhances uterine blood velocity in rats. The reactivity of the uterine artery to alpha-adrenoceptor and muscarinic receptor agonists was higher than that of systemic arteries. Sodium nitroprusside increased uterine arterial blood velocity slightly during gestation and markedly in non-pregnant rats. N(G)-L-Arginine methyl ester (L-NAME) decreased the uterine blood velocity mainly in gravid animals. The effect of diclofenac on uterine blood velocity was also more pronounced during pregnancy. The actions of sodium nitroprusside, L-NAME and diclofenac on systemic blood pressure were similar in pregnant and virgin rats. Altogether, these results indicate that pregnancy enhances nitric oxide (NO) and vasodilatory prostanoid production in the uterine vascular muscle which becomes less sensitive to exogenous NO. The uterine vasodilated status appears to be determined by conjugated actions of endothelial NO and vasodilator prostanoids of which the synthesis and the effects are weakly modified in systemic arteries during gestation.

The effect of 17beta-estradiol on isolated omental arteries from preeclamptic women

OBJECTIVE

To study the effect of 17beta-estradiol on isolated omental arteries from preeclamptic women.

STUDY DESIGN

Rings of omental artery with intact endothelium were mounted in organ chambers for isometric tension recording. We studied the effect of pharmacological concentrations of 17beta-estradiol on potassium chloride-induced tension and the concentration-contraction relationships for norepinephrine and calcium.

RESULTS

Cumulative application of 17beta-estradiol, in a concentration-dependent manner, relaxed potassium chloride contracted rings. Sixty minutes of incubation with 17beta-estradiol (10(-5)mol/l) attenuated the tension developed in response to potassium chloride, norepinephrine and calcium. Tamoxifen (10(-6)mol/l) did not antagonize the inhibitory actions of 17beta-estradiol.

CONCLUSIONS

Pharmacological concentrations of 17beta-estradiol retain the capability for relaxing omental artery rings from preeclamptic women. The loss of refractoriness to norepinephrine, increased responsiveness to calcium ions and decreased ability of 17beta-estradiol to inhibit calcium-induced tension may be responsible for increased vascular reactivity in preeclampsia.

Maternal cocaine use and cigarette smoking in pregnancy in relation to amino acid transport and fetal growth

This review covers the weight of evidence that shows the association of cocaine and cigarette smoking in pregnancy with the impaired transplacental amino acid transport which might give rise to fetal growth restriction (IUGR). Vasoconstrictive effects of both cocaine and nicotine on the placental vasculature are clearly not the only cause for inhibition of placental amino acid uptake and transfer. In vitro studies strongly suggest that cocaine decreases the activity of placental amino acid transport system A and system N, and possibly system l and system y(+), while nicotine decreases the activity of system A. These findings are supported by cordocentesis studies in human IUGR pregnancies not resulting from drug abuse. More work is needed to be done in order to understand the potential additive or synergistic effect of cocaine and cigarette smoking on fetal growth and to determine the underlying cellular mechanisms of interaction with placental amino acid transporters.

Characterization of oxytocin actions in guinea-pig isolated uterine artery: the effect of pregnancy

While the contractile effect of oxytocin on uterine artery has been reported, little is known about whether pregnancy affects the responsiveness of this artery to oxytocin. If it does, is it a consequence of changed endothelial function, as has been proposed for some other vasoconstrictors. Furthermore, the receptor subtypes involved in oxytocin action on uterine artery has not been yet determined. Therefore the purposes of this study were to (1) determine the receptor subtypes involved in oxytocin action in non-pregnant and pregnant guinea-pig uterine artery and to (2) determine whether possible changes in uterine artery sensitivity to oxytocin during pregnancy are due to altered endothelial function. Therefore, the effect of oxytocin on non-pregnant and pregnant guinea-pig uterine arterial rings with and without endothelium was investigated. In non-pregnant guinea-pig uterine artery oxytocin induced contraction (pEC50 = 7.63) with greater potency than in pregnant guinea-pig uterine artery (pEC50 = 7.17). Removal of the endothelium did not affect oxytocin-induced contractions, regardless of the pregnancy status. The uterine arteries did not respond to [Thr4, Gly7]oxytocin. In the preparations studied, [d(CH2)5Tyr(Me)2]vasopressin and [d(CH2)5, D-Ile2, Ile4]vasopressin antagonized oxytocin action with the following pKB values ([d(CH2)5Tyr(Me)2]vasopressin versus [d(CH2)5, D-Ile2, Ile4]vasopressin): 8.24 versus 7.29 and 8.11 versus 7.17 for non-pregnant guinea-pig uterine artery with and without endothelium, respectively; 8.39 versus 7.25 and 8.35 versus 7.25 for pregnant guinea-pig uterine artery with and without endothelium, respectively. We suggest that, in uterine arteries, oxytocin induces contraction by activation of vasopressin V1A receptors. The potency of oxytocin in uterine artery is decreased during pregnancy and this is not associated with altered endothelial function.

Nitric oxide and pregnancy

We have hypothesized that an alteration in the production of endothelium-dependent factors by sex hormones is a potential unifying mechanism for both the decreased arterial contractility and the redistribution of cardiac output characteristic of normal pregnancy. Thus, the effect of pregnancy/ estradiol on any one vascular bed will reflect the number and distribution of estrogen receptors. In this article, we review what is known about the effects of pregnancy and estrogen on nitric oxide synthase. Pregnancy increases Ca(2+)-dependent NOS activity early in gestation. The timing of the increase parallels the increase in plasma estradiol concentration. The increase in maternal brain NOS during pregnancy is blocked by tamoxifen. cGMP content increases along a similar time course in most but not all tissues. The changes in cGMP more closely approximate the changes in blood flow during pregnancy. This suggests that multiple elements of the NO:cGMP pathway are altered by pregnancy. It also shows that cGMP content cannot always be used as a surrogate for NOS activity. Estradiol, but not progesterone or testosterone, increases CA(2+)-dependent NOS activity. NO accounts for some, but not all of the pregnancy-associated changes in maternal arterial contractile response. It is not involved in uterine quiescence. Nitric oxide synthase is developmentally regulated in the fetus and is likely important in regulating the distribution of fetal blood flow.

Loss of endothelium-dependent relaxation in myometrial resistance arteries in pre-eclampsia

OBJECTIVE

To measure endothelium-dependent relaxation in myometrial resistance arteries and to compare this parameter in nonpregnant and normotensive pregnant women and those with pregnancies complicated by pre-eclampsia.

DESIGN

A prospective study.

SETTING

Nottingham City Hospital.

SAMPLE

Thirty-seven nonpregnant women undergoing hysterectomy and 51 pregnant women undergoing caesarean section, of whom there were 39 normotensive and 12 with pre-eclampsia.

METHODS

Resistance arteries, dissected from myometrial biopsies, were mounted on a wire myograph and preconstricted with vasopressin then subjected to incremental doses of bradykinin.

RESULTS

Endothelium-dependent relaxation to bradykinin was seen in the vessels of nonpregnant and normotensive pregnant women. Markedly reduced endothelium-dependent relaxation was found in the myometrial arteries from women with pre-eclampsia when compared with both nonpregnant (P < 0.0001) and normotensive pregnant (P < 0.0001) women.

CONCLUSION

A significant loss of endothelium-dependent relaxation in myometrial resistance arteries in pre-eclampsia may contribute to the altered vasoreactivity seen in pre-eclampsia, and particularly to the decreased placental perfusion and fetal growth retardation commonly associated with this condition.

Effect of chronic treatment with 17beta-estradiol and progesterone on endothelium-dependent and endothelium-independent relaxation in isolated aortic rings from ovariectomized rats

OBJECTIVE

Our purpose was to study the influence of chronic treatment with sex hormones on endothelium-dependent and endothelium-independent relaxation of rat aortic rings.

STUDY DESIGN

Rings of aortas, with and without endothelium, from rats treated with sex hormones or vehicle for 10 days were mounted in organ baths for isometric tension recording. Indomethacin (10(-5) mol/L) and N(omega)-nitro-L-arginine methyl ester (10(-4) mol/L), alone or in combination, were used to block cyclooxygenase and nitric oxide synthase, respectively. Mean data of contraction induced by potassium chloride (60 mmol/L), the relaxation by acetylcholine (10(-6) mol/L) in potassium chloride-contracted rings, tension induced by phenylephrine, and the negative logarithm of the concentration of acetylcholine or 3-morpholinosydnonimine producing a 50% relaxation, and area under the curve were calculated.

RESULTS

Treatment with 17beta-estradiol (10 microg/rat/day) decreased the tension induced by 60 mmol/L potassium chloride and increased the relaxation by acetylcholine in the rings with endothelium precontracted with potassium chloride. Contraction induced by potassium chloride and relaxation induced by acetylcholine were not influenced by the treatment with progesterone (2 mg/rat/day) or estrogen-progesterone combination. Treatment with estradiol, progesterone, or both hormones had no effect on tension developed in intact rings in response to phenylephrine and did not influence endothelium-dependent relaxation to acetylcholine or endothelium-independent relaxation to 3-morpholinosydnonimine in rings contracted with phenylephrine. The inhibition by N(omega)-nitro-L-arginine methyl ester of endothelium-dependent relaxation by acetylcholine was attenuated after the treatment with the sex hormones.

CONCLUSIONS

Chronic treatment with sex hormones did not increase production or release of endothelium-derived relaxing factor and did not change the sensitivity of rat aortic smooth muscle to nitric oxide. The treatment slightly counteracted the inhibition of endothelium-dependent relaxation produced by nitric oxide synthase blocker.

Local regulation of oviductal blood flow

1. Blood flow to the oviduct is implicated in the genesis and maintenance of oviductal fluid, in this way contributing to the creation of an adequate medium for ovum/embryo physiology. Therefore, factors controlling the tone of the vessels supplying the oviduct would be expected to affect its luminal environment. In addition, cyclic changes in oviductal blood flow have been suggested to have mechanical functions in the transport of the ovum/embryo. 2. The vascular supply to the oviduct has a prominent adrenergic vasomotor control. A dense adrenergic innervation, together with the presence of a predominant population of alpha(1)-adrenoceptors, provides a contractile regulatory mechanism of oviductal blood flow. No evidence is available on the presence of beta-adrenoceptors. The scanty cholinergic innervation of mammalian oviduct is mainly confined to the vessels, where acetylcholine (ACh) has a vasodilatory effect by releasing endothelium-derived relaxing factors. 3. The presence of nerves containing neuropeptides has been shown in the oviduct. Specifically, a high density of neuropeptide Y- and vasointestinal peptide-containing nerve fibers has been found in relation to blood vessels, but their role in the neutral control of the oviduct blood flow remains to be established. To date, it is not known whether or not oviductal blood vessels receive perivascular nitrergic nerves. 4. Relaxing and contracting factors derived from endothelium also seem to have a modulatory role on oviductal vascular tone. Neurotransmitters or autacoids, such as ACh and histamine, acting on endothelial receptors, release nitric oxide (NO), which relaxes oviductal arteries through guanylyl cyclase activation and accumulation of cyclic GMP. In addition, the release of an endothelium-derived hyperpolarizing factor (EDHF), distinct from NO, by ACh has been shown in oviductal arteries. It acts through the opening of low-conductance Ca(2+)-activated K+ channels leading to hyperpolarization and relaxation. Furthermore, potent and long-lasting contractions induced by the endothelium-derived contractile factor, endothelin (ET), points to its role in the long-term regulation of oviductal vascular tone. 5. A particularly high density of 5-hydroxytryptamine (5-HT) and histamine, present in mast cells clustered in the vicinity of blood vessels, has been described in the oviduct. It is known that histamine elicits a relaxation of oviductal arteries that is partially endothelium-dependent and mediated by the activation of H1-receptors. The implication of histamine in both the increase in blood flow and edema around ovulation, as well as the existence of a functional antagonism between histamine and 5-HT in the regulation of oviductal blood flow, await further investigation. 6. Other factors, such as relaxing and contracting cyclooxygenase-derived products, may also participate in the modulation of blood flow to the oviduct. 7. An overall endocrine regulation of the oviductal vascular supply exists, acting by both direct effects on smooth muscle and modulation of neural and autocrine factors. This control enables cyclic changes in blood flow to the oviduct that are tightly coupled to the reproductive functions of the tube.

Bradykinin-mediated relaxation of isolated maternal resistance arteries in normal pregnancy and preeclampsia

OBJECTIVE

The aim of the study was to investigate bradykinin-mediated vasodilator function in small arteries from normotensive pregnant and nonpregnant women and from women with preeclampsia.

STUDY DESIGN

Small subcutaneous arteries (approximately 250 microns luminal diameter) were dissected from biopsy specimens obtained at cesarean section from 24 normotensive pregnant women and 6 women with preeclampsia and during abdominal surgery in 15 nonpregnant women. Vascular function was assessed after arteries were mounted on a small vessel myograph.

RESULTS

Preconstricted arteries from normotensive pregnant women demonstrated enhanced relaxation to bradykinin compared with those from nonpregnant women (p < 0.05), whereas arteries from women with preeclampsia showed blunted responses compared with those from normotensive pregnant women (P < 0.01). Relaxation in all groups was attenuated in the presence of the nitric oxide synthase inhibitor N omega-nitro-L-arginine so that it became similar in the three groups. Indomethacin had a small but significant inhibitory effect on bradykinin-induced relaxation, but this component of relaxation was no different among groups. Sensitivity of arteries to norepinephrine and sodium nitroprusside showed no significant differences in the three groups of women.

CONCLUSION

This study provides evidence for an increase in bradykinin-mediated nitric oxide synthesis from the vascular endothelium of small arteries from the peripheral circulation of normotensive pregnant women and a relative reduction in women with preeclampsia. In turn, these changes may contribute to vasodilation in normal pregnancy and elevation of the blood pressure in preeclampsia.

A comparison of endothelium-dependent relaxation in omental and myometrial resistance arteries in pregnant and nonpregnant women

OBJECTIVES

The study aimed to compare endothelium-dependent relaxation in the resistance arteries of the uterine vascular bed by use of a systemic comparison and to investigate the role of the endothelium in adaptation to pregnancy in these vascular beds.

STUDY DESIGN

Myometrial and omental resistance arteries were collected from 22 normotensive pregnant women and 27 nonpregnant women of reproductive age. On a wire myograph and preconstricted with vasopressin, the arteries were relaxed with the endothelium-dependent vasodilator bradykinin.

RESULTS

The omental arteries showed a consistently greater endothelium-dependent relaxation than the myometrial arteries, both in the nonpregnant state (p < 0.0001) and in pregnancy (p = 0.008); pregnancy did not significantly alter this relaxation in arteries from either the myometrial (p = 0.2075) or omental (p = 0.372) vascular beds.

CONCLUSIONS

The endothelium-dependent relaxation to bradykinin is less in myometrial resistance arteries than in omental resistance arteries. There appears to be no intrinsic difference between vessels from nonpregnant and pregnant women in endothelium-dependent response to bradykinin.

The direct action of 17 beta-estradiol in isolated omental artery from nonpregnant and pregnant women is related to calcium antagonism

OBJECTIVE

Our purpose was to study the mechanism by which 17 beta-estradiol modulates contractile activity in isolated rings of omental artery from nonpregnant and pregnant patients.

STUDY DESIGN

Rings of omental artery with intact endothelium from nonpregnant and pregnant women were mounted in organ chambers for isometric tension recording. The concentration-relaxation relationship to 17 beta-estradiol (10(-7) mol/L to 3 x 10(-5) mol/L) was studied in rings contracted with 60 mmol/L potassium chloride (in both the absence and the presence of tamoxifen, 10(-6) mol/L). The effect of 17 beta-estradiol (10(-5) mol/L) on the contraction induced by 60 mmol/L potassium chloride and on the concentration-contraction relationships to both norepinephrine (10(-9) mol/L to 10(-5) mol/L) and calcium ion (0.05 mmol/L to 2.5 mmol/L in calcium-free depolarizing solution) were studied in the presence and absence of tamoxifen (10(-6) mol/L). The maximal contraction, negative logarithm of the concentration producing 50% relaxation or 50% contraction to the reference 60 mmol/L potassium chloride contraction, and the area under the curve were calculated. Data analysis was by one-way analysis of variance, Newman-Keuls test, and two-sample tests as appropriate. Probability values less than 0.05 in a two-tailed test were considered statistically significant.

RESULTS

17 beta-Estradiol relaxed omental arteries contracted with 60 mmol/L potassium chloride, and this effect was potentiated by tamoxifen in both groups. Incubation of the omental arteries with 17 beta-estradiol inhibited contractions induced by 60 mmol/L potassium chloride in rings from both groups of patients, and tamoxifen did not antagonize this effect in either group. Rings of omental artery from the nonpregnant patients (expressed as percentage of the reference potassium chloride contraction) showed greater contraction than rings from the pregnant women when exposed to norepinephrine, a statistically significant difference. 17 beta-Estradiol decreased the norepinephrine-induced contraction in omental arteries from nonpregnant but not pregnant women in a statistically significant way. Tamoxifen did not influence the effect of norepinephrine for either group. 17 beta-Estradiol inhibited calcium ion-induced contraction similarly in rings of omental artery from both nonpregnant and pregnant patients. Tamoxifen potentiated estradiol-induced inhibition in arteries from pregnant patients.

CONCLUSIONS

17 beta-Estradiol inhibits norepinephrine-induced contractions in omental arteries from nonpregnant but no pregnant patients. The inhibition of the ter sion developed after exposure to potassium chloride, norepinephrine, and calcium ion is caused by a calcium channel blocking action.

Human placental monoamine transporters as targets for amphetamines

OBJECTIVES

The use of amphetamine and its derivatives during pregnancy is known to have adverse effects on the outcome of pregnancy. These effects are at least partly a result of impairment of placental function caused by these abusable drugs. We hypothesized that the two monoamine transporters, namely, the serotonin transporter and the norepinephrine transporter, that are expressed in the human placenta are direct targets for these drugs.

STUDY DESIGN

The interaction of amphetamine and methamphetamine with human placental serotonin and norepinephrine transporters was examined. Activity of the serotonin transporter was assessed by serotonin uptake in both maternal-facing brush border membrane vesicles isolated from normal term human placentas and in JAR choriocarcinoma cells. Activity of the norepinephrine transporter was assessed by dopamine uptake and nisoxetine binding in placental brush border membrane vesicles.

RESULTS

Amphetamine and methamphetamine are potent inhibitors of the serotonin and norepinephrine transporters expressed in the human placenta. The inhibitory potency of amphetamine is greater than that of methamphetamine. In each case, the S(+)diastereoisomer is more potent than the corresponding R(-)diastereoisomer. The sensitivity of the norepinephrine transporter to inhibition by these drugs is at least two orders of magnitude greater than that of the serotonin transporter. At concentrations known to occur in the plasma of users, these drugs cause a marked inhibition of the norepinephrine transporter.

CONCLUSIONS

The results show that the norepinephrine transporter and, to a lesser extent, the serotonin transporter are cellular targets in the human placenta for the abusable drugs amphetamine and methamphetamine.

Effect of the vascular endothelium on noradrenaline-induced contractions in non-pregnant and pregnant guinea-pig uterine arteries

1. The effect of pregnancy on noradrenaline-mediated contraction of guinea-pig uterine artery rings with both intact and denuded endothelium was investigated. 2. Noradrenaline (25 nM-100 microM) induced concentration-dependent contraction of non-pregnant and pregnant guinea-pig uterine arterial rings with intact endothelium with similar pD2 and maximal response values (non-pregnant: pD2 = 5.85 +/- 0.02, maximal response = 121 +/- 8.2%; pregnant: pD2 = 5.81 +/- 0.04, maximal response = 122 +/- 9.1%). Removal of endothelium did not affect noradrenaline-induced contractions in non-pregnant guinea-pig uterine artery (pD2 = 5.97 +/- 0.02, maximal response = 119 +/- 8.6%). In contrast, in arteries from pregnant guinea-pigs, removal of endothelium shifted concentration-response curve for noradrenaline to the left, without affecting maximal response value (pD2 = 6.36 +/- 0.03, maximal response = 120 +/- 9.0%). 3. The pKA values for noradrenaline were: 5.76 +/- 0.09 and 5.82 +/- 0.10 for non-pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively and 5.74 +/- 0.09 and 5.72 +/- 0.07 for pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively. 4. The receptor occupancy-response relationship for noradrenaline was linear for all types of vessels, except for pregnant guinea-pig uterine artery with denuded endothelium, since half-maximal response to noradrenaline was obtained with 44.8 +/- 6.9% (non-pregnant guinea-pig uterine artery with intact endothelium), 43.3 +/- 6.1% (non-pregnant guinea-pig uterine artery with denuded endothelium) and 44.3 +/- 6.3% (pregnant guinea-pig uterine artery with intact endothelium) receptor occupancy. In pregnant guinea-pig uterine artery with denuded endothelium, occupancy-response relationship for noradrenaline was non-linear since half-maximal response to noradrenaline was obtained with 19.7 +/- 3.3% receptor occupancy. 5. NG-monomethyl-L-arginine (100 microM) and indomethacin (10 microM) did not affect concentration-response curve for noradrenaline in guinea-pig uterine arteries, regardless of pregnancy status or endothelial condition. 6. In quiescent preparations, the alpha-adrenoceptor antagonists, prazosin (5-50 nM) and yohimbine (1-10 microM) produced parallel rightward shifts of the curves for noradrenaline and the slopes of the Schild plots were not significantly different from unity. The plots constrained to a slope of unity gave the following - log Kb values: prazosin vs. yohimbine 8.78 +/- 0.03 vs. 6.41 +/- 0.02 for non-pregnant guinea pig uterine artery with intact endothelium, 8.95 +/- 0.03 vs. 6.34 +/- 0.02 for non-pregnant guinea-pig uterine artery with denuded endothelium, 8.91 +/- 0.01 vs. 6.44 +/- 0.03 for pregnant guinea-pig uterine artery with intact endothelium and 9.07 +/- 0.01 vs. 6.52 +/- 0.03 for pregnant guinea-pig uterine artery with denuded endothelium.7. It is concluded that initially there is no difference in noradrenaline action between uterine arteries from non-pregnant and pregnant guinea-pigs, but after removal of the endothelium the pregnant guinea-pig uterine artery is more sensitive to noradrenaline, which is related to increased receptor reserve for noradrenaline in this tissue. It is probable that relaxing factor derived from the endothelium mediates this effect, but it is unlikely to be nitric oxide or prostacyclin. Antagonist affinities and affinity of noradrenaline itself suggests that an identical subtype of alpha-adrenoceptor, probably the alpha 1 subtype, is involved in the noradrenaline-induced contraction of non-pregnant and pregnant guinea-pig uterine artery with or without endothelium.

Human placenta: a direct target for cocaine action

Use of cocaine during pregnancy is known to have harmful effects on the mother and her fetus. Currently available models describing the pathogenesis of these effects focus on the involvement of cocaine target systems, primarily the noradrenaline transporter, in the mother and the fetus. The placenta which lies between the mother and the fetus is considered only as a 'silent observer' in the whole process of cocaine-induced complications during pregnancy. Recent studies have, however, shown that the placenta expresses several cocaine target proteins such as the noradrenaline transporter, the serotonin transporter, and the sigma receptor. The functions of these proteins are significantly impaired in the presence of cocaine at concentrations known to exist in the plasma of cocaine users. These studies clearly show that the placenta itself is a direct target for cocaine action and that interaction of cocaine with its target proteins in the placenta plays an important role in the pathogenesis of cocaine-induced complications in the mother and her developing fetus.