Raymond R. Benoit

Potential role of endothelin-1 in normal and hypertensive pregnancies

Endothelins are the most potent naturally occurring vasoconstrictors yet discovered. Both normal and abnormal pregnancies are associated with significant changes in vascular smooth muscle; therefore the potential role of endothelin in pregnancy was investigated. Plasma immunoreactive endothelin-1 concentration was measured by radioimmunoassay in blood from women with normal pregnancy and preeclampsia and in cord blood from normal pregnancies. Endothelin-1 levels were elevated in pregnant women during labor when compared with levels in nonpregnant women and patients with normal pregnancies before labor. Preeclampsia in nonlaboring women before treatment was associated with higher endothelin values when compared with values in normal nonlaboring patients and women with preeclampsia after magnesium sulfate infusion. The umbilical venous concentration of endothelin was 10 times higher than normal pregnant levels and four times higher than levels in laboring patients.

The induction of cyclooxygenase-2 (COX-2) in intact human amnion tissue by interleukin-4

Infection is a major cause of preterm labor. Amniotic fluid from women in preterm labor associated with intrauterine infection contains increased concentrations of cytokines. The mechanism underlying this association may be a cytokine-mediated stimulation of amnion cell prostaglandin production. The biosynthesis of prostaglandins from arachidonic acid is regulated by the enzyme cyclooxygenase which exists in two forms; the constitutive form (COX-1) and the other mitogen inducible (COX-2). The purpose of this study was to evaluate the effect of the cytokine interleukin-4 (IL-4) on cyclooxygenase activity and PGE2 production in amnion. Amnion tissue was taken at caesarean section from term women not in labor and immediately incubated for 2 hours in media containing concentrations of IL-4 ranging from 1 to 100 ng/ml. An increase in both COX-2 enzyme and prostaglandin E2 (PGE2) production was observed for all concentrations of IL-4 greater than 25 ng/ml (P < 0.05, n = 8). No change in COX-1 was observed. Our data suggest that the cytokine IL-4 may be involved in the pathogenesis of premature labor by inducing COX-2 in amnion tissue resulting in increased production of PGE2 and subsequent myometrial activity.

The Effect of Interleukin‐1β and Interleukin‐4 on the Expression of Prostaglandin Receptors EP1 and EP3 in Amnion WISH Cells

PROBLEM: Although prostaglandin E2 (PGE2) is believed to modulate biochemical and immunological events leading to parturition, the role of prostaglandin E receptors during labor has not been investigated.

The effect of magnesium sulfate infusion on systemic and renal prostacyclin production.

Recent in vitro studies have suggested that magnesium sulfate (MgSO4) infusions may increase prostacyclin production. We studied the effect of MgSO4 infusion on prostacyclin (PGI2) metabolite excretion in women with either pregnancy induced hypertension or preterm labor. Excretion of renal and systemic metabolites of PGI2 was measured prior to and following the start of MgSO4 infusion in the two groups. An increased in renal PGI2 metabolite preterm labor excretion was noted in the hypertension group but no change was noted in systemic PGI2 excretion in either group. These data fail to support a generalized, short term increase in endothelial cell PGI2 production as the basis for the beneficial effect of MgSO4.

Corticotropin-Releasing Hormone Increases the Expression of the Prostaglandin E2 Receptor Subtype EP1 in Amnion WISH Cells

Abstract The purpose of this study was to investigate the effect of corticotropin-releasing hormone (CRH) on the expression of the prostaglandin (PG) E2 EP1 receptor subtype and PGE2 production in amnion WISH cells (AWC). AWC cultures were incubated with CRH. Culture fluid was collected for PGE2 measurement, and the cells were collected and analyzed for EP1 protein and mRNA. Immunohistochemical localization of the EP1 receptor was also performed. Incubation of AWC with CRH resulted in a dose-dependent increase (r = 0.97) in the level of EP1 receptor protein (P < 0.001). Coincubation of AWC with CRH and indomethacin resulted in the decreased production of PGE2 while having no effect on EP1 receptor expression. A significant but not dose-dependent increase in EP1 mRNA expression was also observed (P < 0.01). Immunohistochemical evaluation verified cell membrane localization of the receptor in both stimulated and unstimulated cells and confirmed the increased expression of EP1 receptor in response to CRH. Incubation of AWC with CRH also resulted in increased culture fluid PGE2 levels (P < 0.01). These results suggest that the role CRH plays in the initiation of labor may also involve the promotion of elevated PGE2 levels and increased expression of the EP1 receptor in amnion.

Modulation of the prostaglandin E receptor : A possible mechanism for infection-induced preterm labor

OBJECTIVE To evaluate the modulatory effects of interleukin (IL)-1beta and prostaglandin (PG)E2 on the PGE2 receptor subtype EP1 in amnion cell cultures. METHODS Amnion cell cultures were incubated in increasing concentrations of (IL)-1beta or PGE2. Cultures were also incubated in high concentrations of IL-1beta and PGE2 in combination. Changes in EP1 receptor levels were evaluated by western and northern blot analysis. Culture fluid PGE2 levels were measured by enzyme-linked immunosorbent assay. RESULTS EP1 receptor protein levels decreased with increasing levels of PGE2 (r = -0.82, P < .05). EP1 receptor protein (r = 0.95, P < .05), EP1 mRNA (r = 0.95, P < .01), and culture fluid PGE2 levels (P < .01) were all increased after IL-1beta administration. EP1 receptor levels also increased approximately fourfold in response to IL-1beta incubation even in the presence of high agonist (PGE2) concentrations (P < .01). CONCLUSION The results of this study show that IL-1beta might be involved in infection-induced preterm labor by interfering with the normal regulation of EP1 receptor levels and with the promotion of increased PGE2 production in amnion tissue.

Serum prostacyclin binding and half-life in the umbilical circulation.

Serum prostacyclin binding and half-life was measured in twenty pairs of maternal and umbilical venous samples and in twenty non-pregnant controls. When compared to non-pregnant values both umbilical and maternal samples demonstrated significantly lower albumin concentrations, percentage of prostacyclin binding and shorter prostacyclin half-life.

Influence of albumin and non-esterified fatty acids on serum prostacyclin binding in pregnancy

We investigated the etiology of the previously documented decrease in serum prostocyclin binding during pregnancy. Addition of albumin to the serum of pregnant women failed to raise binding to non-pregnant levels. Pregnancy serum bound significantly more prostacyclin following the removal of non-esterified fatty acids and the addition of fatty acid free albumin resulted in a rise in binding to non-pregnant levels. We conclude that serum protein prostacyclin binding is affected by both albumin concentration and non-esterified fatty acids.

The association between apolipoprotein A-I and prostacyclin binding in human serm

Abstract The stability of Prostacyclin in human blood is dependent upon binding to circulating proteins. Although this binding has been considered to be primarily due to albumin, a recent report has suggested that apolipoprotein A-I is responsible. We compared prostacyclin binding to the concentratio of albumin and apolipoprotein A-I in several groups of sera with known diffrences in the ability to bind prostacyclin. Our results indicate a strong correlation with albumin concentration but no correlation between binding and the concentration of apolipoprotein A-I. It appears that in the human circulation albumin concentration is the most important determinant of prostacyclin binding.

The induction of cyclooxygenase-2 by interleukin-4 in human umbilical vein endothelial cells: A possible role in regulation of fetal vascular tone

OBJECTIVE We sought to determine a possible role for interleukin-4 in the control of umbilical cord blood flow by evaluating its effect on cyclooxygenase-2 production of a vasoactive prostaglandin. STUDY DESIGN Human umbilical vein endothelial cells in culture were incubated for 16 hours in media containing interleukin-4 in concentrations from 5 to 100 ng/ml. Prostaglandin E2 concentrations in the culture media were measured using a monoclonal enzyme-immunoassay. Concentrations of cyclooxygenase-1 and cyclooxygenase-2 were determined by Western blot analysis on cell homogenates. Statistical comparisons between prostaglandin E2, cyclooxygenase-1, and cyclooxygenase-2 concentrations for each interleukin-4 concentration were performed using a one way analysis of variance. RESULTS Incubation of human umbilical vein endothelial cells in media containing interleukin-4 resulted in a significant increase in both prostaglandin E2 and cyclooxygenase-2 for interleukin-4 concentrations greater than 50 ng/ml (p < 0.05). Cyclooxygenase-1 levels were not affected. CONCLUSIONS We suggest that interleukin-4 may have a role in the regulation of umbilical blood flow mediated through the induction of cyclooxygenase-2.