Influence of Lipopolysaccharide on the Uterine Contraction Inhibitory Effects of Tocolytic Agents in Pregnant Mice

ABSTRACT

The study was undertaken to investigate the influence of lipopolysaccharide (LPS) on the uterine contraction inhibitory effects of tocolytic agents such as ritodrine, magnesium, and diethylamine/nitric oxide (DEA/NO), and on prostaglandin (PG) E2 and nitric oxide (NO) metabolite (NOx) production in pregnant mice at midgestation. Pregnant C57BL mice on day 14 of gestation were sacrificed 6 hours after intraperitoneal injection of LPS (400 μg/kg) or vehicle. Uterine rings were equilibrated in Krebs-Henseleit solution (37°C) bubbled with 20% O₂ and 5% CO₂ (pH ~7.4) for sampling and isometric tension recording. The concentration levels of PGE2 and NOx in the solution were determined. Changes of spontaneous contractile activity in response to cumulative concentrations of ritodrine, magnesium, and the NO donor, DEA/NO, from the baseline were determined. Integral contractile activity over 10 minutes at each concentration was calculated and expressed as percentage change from basal activity. Statistical analysis was performed using one-way analysis of variance (ANOVA) followed by the Dunnett test (significance: p < 0.05). LPS treatment significantly increased the production levels of PGE2 and NOx (from 66.8 ± 6.7 pg/g tissue to 147.0 ± 29.0, from 51.0 ± 5.4 pmol/2 μL/g tissue to 98.0 ± 16.2, respectively), p < 0.05). Ritodrine, magnesium, and DEA/NO inhibited spontaneous contractions concentration dependently in uterine rings from both LPS-treated and -untreated animals. Treatment with LPS significantly attenuated the maximal inhibition induced by DEA/NO in uterine rings from pregnant mice. LPS significantly suppressed the uterine contraction inhibitory effects of ritodrine at 10^-8 M concentrations and of magnesium at 4.2 mmol concentration (p < 0.05). We concluded that the effects of ritodrine and magnesium may be reduced under inflammatory conditions because LPS increases the production levels of PGE2 and NOx, which cause increased spontaneous contractions of the uterine myometrium. Therefore, when uterine contractions are not controlled by tocolytics in pregnant patients with preterm labor associated with inflammation, labor induction or pregnancy termination may become significant options in clinical practice.

KEYWORDS

Ritodrine - magnesium - PGE2 - nitric oxide - contractility - lipopolysaccharides - myometrium

REFERENCES

• 1 Gomez R, Romero R, Edwin S S, David C. Pathogenesis of preterm labor and preterm premature rupture of membranes associated with intraamniotic infection.  Infect Dis Clin North Am. 1997;  11 135-176
• 2 Klein L L, Gibbs R S. Infection and preterm birth.  Obstet Gynecol Clin North Am. 2005;  32 397-410
• 3 Kazy Z, Puho E, Czeizel A E. Effect of vaginal metronidazole + miconazole treatment during pregnancy for gestational age and birth weight in a population-based study.  Arch Gynecol Obstet. 2005;  272 294-297
• 4 Kazy Z, Puho E H, Czeizel A E. The possible preterm birth preventive effect of ampicillin during pregnancy.  Arch Gynecol Obstet. 2006;  274 215-221
• 5 Souney P F, Kaul A F, Osathanondh R. Pharmacotherapy of preterm labor.  Clin Pharm. 1983;  2 29-44
• 6 Romero R, Mazor M, Wu Y K et al.. Infection in the pathogenesis of preterm labor.  Semin Perinatol. 1988;  12 262-279
• 7 Gibbs R S, Romero R, Hillier S L, Eschenbach D A, Sweet R L. A review of premature birth and subclinical infection.  Am J Obstet Gynecol. 1992;  166 1515-1528
• 8 Wenstrom K D, Andrews W W, Hauth J C, Goldenberg R L, DuBard M B, Cliver S P. Elevated second-trimester amniotic fluid interleukin-6 levels predict preterm delivery.  Am J Obstet Gynecol. 1998;  178 546-550
• 9 Okawa T, Suzuki H, Yanagida K et al.. Effect of lipopolysaccharide on uterine contractions and prostaglandin production in pregnant rats.  Am J Obstet Gynecol. 2001;  184 84-89
• 10 Ross R G, Sathishkumar K, Naik A K et al.. Mechanism of lipopolysaccharide-induced changes in effect of contractile agonists on pregnant rat myometrium.  Am J Obstet Gynecol. 2004;  190 523-540
• 11 Okawa T, Syal A, Vedernikov Y, Chwalisz K, Saade G R, Garfield R E. The effect of nitric oxide on the contractility of isolated uterine and aortic rings from pregnant rats.  Am J Obstet Gynecol. 1998;  179 721-726
• 12 Okawa T, Asano K, Takahashi H et al.. iNOS mRNA and inhibitory effect of NO on uterine contractile activity in rats are determined by local rather than systemic factors of pregnancy.  J Pharmacol Sci. 2004;  95 349-354
• 13 Lees C C, Lojacono A, Thompson C et al.. Glyceryl trinitrate and ritodrine in tocolysis: an international multicenter randomized study. GTN Preterm Labour Investigation Group.  Obstet Gynecol. 1999;  94 403-408
• 14 Leszczynska-Gorzelak B, Laskowska M, Marciniak B, Oleszczuk J. Nitric oxide for treatment of threatened preterm labor.  Int J Gynaecol Obstet. 2001;  73 201-206
• 15 Minkoff H. Prematurity: infection as an etiologic factor.  Obstet Gynecol. 1983;  62 137-144
• 16 Gomez R, Romero R, Edwin S S, David C. Pathogenesis of preterm labor and preterm premature rupture of membranes associated with intraamniotic infection.  Infect Dis Clin North Am. 1997;  11 135-176
• 17 Roberts J M. Current understanding of pharmacologic mechanisms in the prevention of preterm birth.  Clin Obstet Gynecol. 1984;  27 592-605
• 18 Hall D G, McGaughey Jr H S, Corey E L. The effects of magnesium therapy on the duration of labor.  Am J Obstet Gynecol. 1959;  78 27-32
• 19 Hollander D I, Nagey D A, Pupkin M J. Magnesium sulfate and ritodrine hydrochloride: a randomized comparison.  Am J Obstet Gynecol. 1987;  156 631-637
• 20 Saade G R, Taskin O, Belfort M A, Erturan B, Moise Jr K J. In vitro comparison of four tocolytic agents, alone and in combination.  Obstet Gynecol. 1994;  84 374-378
• 21 Colbert W E, Wilson B F, Williams P D, Williams G D. Relationship between in vitro relaxation of the costo-uterine smooth muscle and mesovarial leiomyoma formation in vivo by beta-receptor agonists.  Arch Toxicol. 1991;  65 575-579
• 22 Weiner C P, Thompson L P. Nitric oxide and pregnancy.  Semin Perinatol. 1997;  21 367-380
• 23 Yallampalli C, Buhimschi I, Chwalisz K et al.. Preterm birth in rats produced by the synergistic action of a nitric oxide inhibitor (NG-nitro-L-arginine methyl ester) and an antiprogestin (onapristone).  Am J Obstet Gynecol. 1996;  175 207-212
• 24 Tobai H, Nishiya I. Nitric oxide mediates inhibitory effect of interleukin-1beta on estrogen production in human granulosa-luteal cells.  J Obstet Gynaecol Res. 2001;  27 53-59
• 25 Jana B, Andronowska A, Kucharski J. Immunoreactivity of iNOS in porcine uterus after infusions of Escherichia coli endotoxin.  Folia Histochem Cytobiol. 2001;  39 177-178
• 26 Nakatsuka M, Asagiri K, Noguchi S, Habara T, Kudo T. Nafamostat mesilate, a serine protease inhibitor, suppresses lipopolysaccharide-induced nitric oxide synthesis and apoptosis in cultured human trophoblasts.  Life Sci. 2000;  67 1243-1250
• 27 Chen G, Wang S H, Warner T D. Regulation of iNOS mRNA levels in endothelial cells by glutathione, a double-edged sword.  Free Radic Res. 2000;  32 223-234
• 28 Hameed C, Tejani N, Verma U L, Archbald F. Silent chorioamnionitis as a cause of preterm labor refractory to tocolytic therapy.  Am J Obstet Gynecol. 1984;  149 726-730