Elsevier

Placenta

Volume 26, Issue 10, November 2005, Pages 758-765
Placenta

Effect of in vivo administration of epidermal growth factor on prostaglandin production and NOS activity in term rat placentae. Possible participation of placental EGF receptors

https://doi.org/10.1016/j.placenta.2004.10.011Get rights and content

Many authors hypothesize that the epidermal growth factor (EGF) is involved in the onset of labor. Previous reports from our laboratory showed that intrauterine administration of EGF delays the beginning of labor. The aims of this study were: 1) to analyze the effect of intrauterine administration of 500 ng EGF on placental prostaglandins and nitric oxide, and 2) to characterize the expression of EGF receptors (EGF-R) in pregnant rat placentae. Saline solution (sham group) and 500 ng EGF (EGF-treated group) were administered via intrauterine injection on day 21 of gestation, and both groups of animals were sacrificed on day 22 (sham rats delivered on day 22). Results showed that EGF treatment: 1) inhibited the production of prostaglandin E (p < 0.001) and F (p < 0.01), 2) increased the synthesis of nitric oxide (p < 0.001), and 3) reduced the expression of cyclooxygenase-II, the enzyme responsible for PG synthesis. Placentae were found to express EGF-R and its activated form, and the expressions of both forms were higher at mid and term pregnancy. Hence, EGF is a very interesting molecule for studying the regulation of placental prostaglandin and nitric oxide production related to the parturition process.

Introduction

Epidermal growth factor (EGF) was first discovered by Cohen in submaxillary glands of mice [1]. From then on, most EGF studies have been focused on the stimulation of in vivo and in vitro cell proliferation. However, EGF seems to display other biological activities as well. It is present in maternal and fetal blood and in the amniotic fluid [2], [27]. It is also believed to be involved in feto-placental growth and development through its mitogenic action, increasing placental and fetal membrane hormone secretion [3]. It has been reported that, in 4–5 week human placentae, EGF and its receptor (EGF-R) are located in cytotrophoblasts, and that EGF increases cytotrophoblast cell proliferation without affecting their ability to secrete human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) [4]. In contrast, in 6–12 week placentae, EGF and its receptor are located in syncytiotrophoblasts and EGF stimulates hCG and hPL secretion without affecting syncytiotrophoblast cell proliferation. Previous studies carried out in our laboratory [5] showed that intrauterine (i/u) administration of 500 ng EGF to 21-day pregnant rats delayed the onset of parturition 19.0 ± 0.6 h (EGF-treated rats delivered on day 23 of pregnancy instead of day 22 as sham animals). Our results also demonstrated that exogenous EGF elicited its effect modulating nitric oxide (NO) and prostaglandin (PG) production in the uterus.

It is well known that, in mammals, NO plays an important role during pregnancy regulating myometrial relaxation and placental circulation [6], [7]. Likewise, the ability of the villous vascular tree of human term placenta to both generate and respond to NO, and the significant role of NO in the maintenance of adequate fetal–placental circulation have also been demonstrated [8]. Moreover, three NOS isoforms have been identified in placental tissue: neuronal (nNOS), endothelial (eNOS) and inducible NOS (iNOS) [9].

On the other hand, PGs are active lipid mediators involved in the parturition process [10]. Their biosynthesis is catalyzed by the cyclooxygenase enzyme (COX), of which two isoforms are known: COX-I and COX-II [11]. Even though the uterus is the main target of PGs during parturition, it is not the primary source of these lipid mediators. It has been proposed that PGs derived from feto-placental tissues is the way by which they reach the uterus generating the contractions necessary for the expulsion of the fetus.

Since the placenta is a complex tissue located in close contact with the uterus [12], the first aim of our study was to investigate whether the placenta was also related to EGF-delayed labor onset mechanism. Thus, we analyzed if i/u administration of 500 ng EGF administered on day 21 of gestation regulated NOS and COX systems in this tissue.

Specific receptors for EGF were detected in fully developed placentae from pregnant mares [13], cats [14], mice [15] and women [16]. However, no descriptions can be found on the expression of EGF-R in placentae from pregnant rats. Therefore, our second aim was to characterize the expression of EGF-R in placentae from mid and term pregnant rats.

Section snippets

Drugs and reagents

Epidermal Growth Factor (murine submaxillary glands, culture grade, PM = 6100) was purchased from Calbiochem, Norabiochem Corporation (La Jolla, CA). [14C]-l-citrulline, [5,6,8,9,11,12,14,15(n)-3H]-prostaglandin F (160 Ci/mmol) and [5,6,8,9,11,12,14,15(n)-3H]-prostaglandin E (130 Ci/mmol) were from Amersham Corporation (Arlington Heights, IL, USA). Monoclonal nNOS, eNOS and iNOS first antibodies were from Transduction Co. (Devon, United Kingdom), whereas polyclonal COX-I, COX-II, EGF-R and EGF-pR

Effect of i/u EGF administration on PG synthesis

We decided to investigate if the delay in the onset of labor caused by the administration of EGF was due to a modulation on PG synthesis in the placenta. Therefore, we compared PG production in sham and EGF-treated rats.

We found that i/u administration of 500 ng EGF on day 21 of gestation significantly decreased both PGE (Figure 1A) and PGF (Figure 1B) production in placentae. Placentae from EGF-treated rats produced less PGs during day 22 than those from sham animals (50% PGE2 and 33% PGF).

Effect of i/u EGF administration on NO production

Discussion

The placenta is known to be an exceedingly rich source of receptors for several growth factors including EGF. This factor, which is primarily mitogenic for a variety of cells and also affects differentiated cellular functions in the absence of a mitogenic effect, is presumed to play a role not only in feto-placental development, but also as a signal during labor.

Previous results from our laboratory show that intrauterine administration of EGF to pregnant rats delays the onset of labor [5].

Acknowledgments

We would like to thanks Mrs. Ana Inés Casella and Ramona Morales for their technical assistance.

This work was supported by PICT 98, Project 05-04426 and FONDECYT 1040804.

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