Yuri P. Vedernikov

Effect of chronic treatment with 17β-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.

Effects of estradiol-17β and progesterone on isolated human omental artery from premenopausal nonpregnant women and from normotensive and preeclamptic pregnant women

OBJECTIVE Our purpose was to study the direct vascular effects of estradiol-17 beta and progesterone on isolated omental artery from premenopausal nonpregnant women and from normotensive and preeclamptic pregnant women. STUDY DESIGN Omental artery rings from normotensive premenopausal nonpregnant women and from normal and preeclamptic pregnant women were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. The endothelium was removed from some of the rings, and all were contracted with potassium chloride (60 mmol/L) and then exposed to cumulative concentrations of estradiol-17 beta and progesterone. Concentration response curves were constructed and relaxation was expressed as percent change from the reference 60 mmol/L potassium chloride contraction. Data analysis was by repeated-measures analysis of variance, Newman-Keuls test, and the unpaired Student t test as appropriate. A two-tailed p < 0.05 was considered statistically significant. RESULTS Both hormones studied caused vasorelaxation in omental arteries from all three groups of patients. Of the two, estradiol-17 beta was more effective, regardless of the presence or absence of endothelium. Removal of the endothelium shifted the estradiol-17 beta concentration-response curve to the right in the normal pregnant artery but not in nonpregnant or preeclamptic vessels. Removal of the endothelium shifted the progesterone concentration-response curve to the left in arteries from preeclamptic patients. CONCLUSIONS Estradiol-17 beta and progesterone have direct in vitro vasodilator activity that appears to be linked, in part, to the endothelium in human omental artery from normal and hypertensive women in different hormonal states.

Effect of nitric oxide and carbon monoxide on uterine contractility during human and rat pregnancy

OBJECTIVE We sought to study the effects of authentic nitric oxide and carbon monoxide on the contractile activity of pregnant human and rat myometrium. STUDY DESIGN Strips were prepared from uterine biopsy specimens of 10 pregnant, nonlaboring women at term gestation undergoing cesarean delivery. In addition, rings were prepared from the uteri of pregnant rats at midterm (day 14) and at term (day 22) gestation (n = 10-12). The tissues were mounted in organ chambers filled with Krebs-Henseleit solution continuously aerated with 5% carbon dioxide in air (37 degrees C, pH approximately 7.4) for isometric tension recording. The effects of nitric oxide and carbon monoxide gases on spontaneous contractile activity were studied. Responses to hemin (hemoxygenase substrate), which produces endogenous carbon monoxide, were also examined. Responses to nitric oxide and carbon monoxide were also studied in aortic and tail artery rings from pregnant rats after contraction with phenylephrine. RESULTS Nitric oxide significantly inhibited contractility of human myometrium at term (area under the concentration-response curve, 145.36 +/- 30.02 vs 40.56 +/- 22.81 in controls; P <.05) and rat myometrium at midterm gestation (264.23 +/- 47.86 vs 121.82 +/- 23.50; P <.05) but not at term. No statistically significant inhibition was induced in human or rat myometrium by carbon monoxide, whereas hemin significantly attenuated contractility in human myometrium at term and in rat myometrium at midterm gestation (P <. 05). Nitric oxide, carbon monoxide, and hemin relaxed aortic and tail artery rings. CONCLUSIONS Authentic nitric oxide inhibits rat uterine contractile activity at midterm gestation but not at term. However, nitric oxide inhibits human myometrium activity at term. Authentic carbon monoxide does not appear to modulate uterine contractility, whereas hemin may have some inhibitory properties.

Vascular reactivity in preeclampsia.

It has long been known that vascular reactivity is altered in preeclamptic patients compared with normal pregnant women. This change even occurs weeks earlier than any clinical manifestation of the disease. Many investigators believe that the conditions for the development of preeclampsia are set as early as the first trimester. These changes in vascular reactivity appear to be independent of the blood pressure because they also occur in chronic hypertensive women destined to have preeclampsia. This review focuses on these changes in vascular reactivity reported in preeclampsia. Increased reactivity of the blood vessels in preeclampsia has been described in most, but not all, studies. The cause for the differences in reactivity between vessels from preeclamptic and normal pregnant women is not known. However, it cannot be attributed solely and with certainty to abnormalities in endothelium-dependent relaxation or the nitric oxide system because the study results published to date remain contradictory. In addition to functional differences, vessels from normal pregnant and preeclamptic women show distinct mechanical properties.

Roles of potassium channels and nitric oxide in modulation of uterine contractions in rat pregnancy

OBJECTIVE We sought to study the involvement of potassium channels in the inhibition by nitric oxide of spontaneous contractions in isolated uterine rings from midterm and term pregnant rats. STUDY DESIGN Uterine rings from Sprague-Dawley rats at midterm and term gestation were used for isometric tension recording. The inhibition of spontaneous contractile activity by potassium channel openers and nitric oxide was studied in the absence and presence of potassium channel inhibitors. RESULTS The adenosine triphosphate-dependent potassium channel opener levcromakalim inhibited spontaneous contractions in rings from both midterm and term pregnant rats in a concentration-dependent manner, and the effects were significantly attenuated by pretreatment with selective inhibitor of the adenosine triphosphate-dependent potassium channel inhibitor glibenclamide. The opener of calcium-dependent potassium channel NS 1619 inhibited spontaneous contractions in rings from midterm but significantly less so in rings from term pregnant rats in a concentration-dependent manner, and the effect was significantly attenuated by pretreatment with potassium channel inhibitors tetraethylammonium and tetrabutylammonium but not with glibenclamide. Rings from midterm and term pregnant rats were more sensitive to the inhibitory effect of levcromakalim compared with NS 1619. Nitric oxide donor diethylamine-nitric oxide inhibited spontaneous contractions in rings from midterm but significantly less in rings from term pregnant rats in a concentration-dependent manner, and the effect was attenuated by tetraethylammonium and tetrabutylammonium but not by glibenclamide. CONCLUSIONS There is gestational age-dependent refractoriness to calcium-dependent potassium but not adenosine triphosphate-dependent potassium channel opener-induced inhibition of spontaneous contractile activity of isolated rat uterine rings. Nitric oxide inhibits uterine contractions by opening of calcium-dependent potassium channels in pregnant rat myometrium. Refractoriness to nitric oxide toward term may result from decreased probability to open or number of calcium-dependent potassium channels.

Effects of selected vasoconstrictor agonists on isolated omental artery from premenopausal nonpregnant women and from normal and preeclamptic pregnant women

OBJECTIVE Our purpose was to compare the responsiveness of omental resistance arteries from nonpregnant women and from normotensive and preeclamptic pregnant women to selected contractile agonists. STUDY DESIGN Omental artery rings with intact endothelium from normotensive premenopausal nonpregnant women and from normal and preeclamptic pregnant women were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. After the presence of endothelium was confirmed, cumulative concentrations of norepinephrine, serotonin, U46619, and endothelin-1 were added. Concentration-response curves were constructed and expressed as percentage of a reference 60 mmol/L potassium chloride contraction. Data analysis was by repeated-measures analysis of variance. Newman-Keuls test, and paired or unpaired Student t test, as appropriate. Statistical significance was by two-tailed p<0.05. RESULTS Endothelin-1 and U46619 increased tension similarly in all three groups. Norepinephrine increased tension in nonpregnant vessels to a greater extent than in either preeclamptic or pregnant vessels (nonpregnant 114.3 +/- 5.42% vs pregnant 65.2 +/- 10.5%, p<0.05). Nonpregnant omental artery developed significantly greater tension than did pregnant tissue at three concentrations of norepinephrine (10(-5) mol/L, 3 x 10(-5) mol/L, 10(-4) mol/L), and preeclamptic vessels developed more tension than that from normal pregnant vessels at 3 x 10(-6) mol/L (p=0.06) and 10(-5) mol/L (p<0.05). There was a negligible change in tension with increasing concentrations of serotonin in the vessels from nonpregnant women; serotonin-induced contraction in the omental arteries from normotensive pregnant women and preeclamptic patients was <6% of the potassium chloride reference contraction, but this was significantly (p<0.05) different from that of the nonpregnant women. CONCLUSIONS Omental artery segments from nonpregnant, normotensive pregnant and preeclamptic women contract similarly to endothelin-1 and U46619 but exhibit variable responses to norepinephrine and serotonin.

IgE-Independent Mast Cell Activation Augments Contractility of Nonpregnant and Pregnant Guinea Pig Myometrium

Background: We have previously shown that in sensitized guinea pigs premature labor can be induced by a type I hypersensitivity reaction. We further hypothesize that premature labor occurs due to increased uterine contractility caused by activation of mast cells and possibly eosinophils, and collective release of their mediators. The objective of this study was to test the hypothesis that IgE-independent mast cell degranulation could increase uterine contractility. Methods: Longitudinal uterine strips from nonpregnant and pregnant guinea pigs were incubated in organ chambers with vehicle, histamine H1, serotonin 5-HT2/5-HT1C, thromboxane A2, leukotriene D4 receptor antagonists, mast cell stabilizer, and cyclooxygenase or lipoxygenase inhibitors. Then, supernatant, obtained after activation of a mast cell line (MC/9) with compound 48/80, culture medium, or compound 48/80 alone were added. Cumulative concentration-response curves to histamine and serotonin were also obtained. Results: The supernatant and compound 48/80 significantly increased contractility of uterine strips. A mast cell stabilizer considerably reduced the effect of compound 48/80. Other substances attenuated uterine contractile responses to supernatant and compound 48/80, and responses varied depending on the pregnancy period. Histamine and serotonin increased contractility of uterine strips, and uterine sensitivity to these agents were dependent on gestational age. Conclusions: In summary, mast cells increase uterine contractility through multiple mediators, and uterine responses to these mediators are dependent on gestational age. We postulate that the simultaneous release of these mast cell/eosinophil mediators in the uterus could be a stimulus to trigger and/or maintain myometrial contractions during preterm and term labor.

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

OBJECTIVE Our purpose was to study the effects of some drugs frequently used in pregnant women on isolated human umbilical artery and vein segments. STUDY DESIGN Umbilical artery and vein rings from normal term pregnancies were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. Rings were contracted with potassium chloride (60 mmol/L) or U46619 (10(-8) mol/L) and then exposed to cumulative concentrations of nimodipine, nifedipine, nicardipine, phenytoin, magnesium sulfate, and hydralazine. Concentration-response curves were constructed by means of the difference in the percent relaxation between test and control vessels. Data analysis was by repeated measures analysis of variance, Newman-Keuls test, and the unpaired Student t test as appropriate. A value of p < 0.05 was considered statistically significant. RESULTS All the agents studied were effective umbilical vasodilators, except for hydralazine, which had minimal effect. The dihydropyridine calcium antagonists were more potent vasodilators than were the other agents studied. Nifedipine was the most potent calcium blocker and was the only dihydropyridine that relaxed the umbilical vein to a greater extent than the umbilical artery. CONCLUSION The most commonly used drugs in preeclampsia have variable effects on the umbilical vessels.

The effects of nitric oxide on the contractility of isolated uterine and aortic rings from pregnant rats

OBJECTIVE The object was to compare the effects of nitric oxide on isolated uterus and aorta of pregnant rats. STUDY DESIGN Rings of uterus and thoracic aorta without endothelium from Sprague-Dawley rats at mid and late gestation were used for isometric tension recording. The concentration-response curve for diethylamine/nitric oxide was studied in the presence or absence of oxyhemoglobin (10(-5) mol/L), or oxyhemoglobin was added after the response to diethylamine/nitric oxide. RESULTS Diethylamine/nitric oxide concentration dependently inhibited uterine contractions, and the effect was attenuated by previous treatment with oxyhemoglobin at mid gestation (n = 8). The effects were negligible at late gestation (n = 8). The relaxation of aortic rings by diethylamine/nitric oxide and its attenuation by previous treatment with oxyhemoglobin were similar at mid (n = 6) and late (n = 6) gestation. The sensitivity of aortic rings to diethylamine/nitric oxide is significantly higher than that of uterine rings. Oxyhemoglobin partly restored inhibited diethylamine/nitric oxide phenylephrine tension in aortic rings and had no effect on diethylamine/nitric oxide-inhibited uterine rings. CONCLUSIONS Uterine smooth muscle is less sensitive to nitric oxide than is aortic smooth muscle. Nitric oxide sensitivity of rat uterus but not aorta decreases toward term.

Sex hormone effects in non-pregnant rat and human myometrium

OBJECTIVE To study effects of sex hormones on spontaneous contractility and on the effects of depolarizing agent potassium chloride (KCl), M-cholinoceptor and prostaglandin receptor agonists on non-pregnant rat and human uterine tissues. STUDY DESIGN Uterine rings from ovariectomized rats treated with sex hormones or placebo, and uterine strips from premenopausal and postmenopausal women were equilibrated in Krebs buffer (t=37 degrees C, pH approximately 7.4) for isometric tension recordings. Spontaneous contractile activity and contractions in response to KCl, eicosanoids, and acetylcholine were compared. RESULTS In tissues from ovariectomized rats, spontaneous contractility was increased, while KCl-induced contractions were decreased. Treatment with 17beta-estradiol, but not progesterone, inhibited spontaneous contractions, but potentiated KCl evoked contractions. Treatment with 17beta-estradiol did not influence responses to prostanoids in ovariectomized rats, while treatment with both sex hormones restored decreased the responses. Spontaneous contractility and responses to KCl were less in uterine tissues from postmenopausal versus premenopausal women. Hormone replacement therapy partly restored the responses to KCl, prostanoids, and acetylcholine. CONCLUSIONS Ovarian steroids modulate spontaneous contractile activity, responses to depolarization, prostanoids and M-cholinoceptor activation in non-pregnant rat and human uterine tissues in vitro.