Prostaglandin E2 Receptor Expression in Fetal Baboon Lung at 0.7 Gestation After Betamethasone Exposure

Abstract

ABSTRACT:The fetal lung produces and metabolizes prostaglandin (PG) E 2. In vitro PGE 2 induces surfactant production via E prostaglandin (EP) 1 and cyclic adenosine monophosphate (cAMP)-coupled EP (EP 2 and EP 4 ) receptors. Glucocorticoids alter PG function and increase lung function in preterm neonates. We hypothesized that fetal exposure to maternally administered betamethasone (␤M) enhances fetal lung EP 1 and cAMP-coupled EP receptor expression. Pregnant baboons were injected intramuscularly (i.m.) with either ␤M (n ϭ 7) or saline [control (CTR); n ϭ 8] at 0.7 gestation. Fetal lungs were removed at cesarean section 48 h after the first injection. We determined mRNA levels, protein localization and abundance for all four PGE 2 receptors by real-time polymerase chain reaction (PCR), immunohistochemistry, and Western blot. EP receptors were widely distributed in bronchiolar epithelium, bronchiolar smooth muscle, and endothelium and media of blood vessels, but not alveoli. Compared with CTR, ␤M exposure resulted in a twofold EP 2 mRNA decrease (p Ͻ 0.05) in male fetuses only. EP 1 , EP 3 , and EP 4 receptor mRNA levels were unaffected. Western blot analysis showed no alteration in EP receptor protein expression. In summary, this is the first demonstration of the four EP receptors in fetal lung. The only change after 48-h ␤M exposure was a gender-specific decrease in EP 2 receptor mRNA. PGE 2 is produced (5,6) and metabolized in the fetal lung (6,7). PGE 2 tranduces its signal via seven-transmembrane domain, G protein-coupled receptors, called EP receptors (8). The EP receptor family has been further classified into four subtypes, EP 1 , EP 2 , EP 3 , and EP 4 (9), differing in their structure, ligand-binding affinities, and signal transduction pathways (8). EP 1 and EP 3 receptors, linked to the Ca 2ϩ / phospholipase C pathway, cause smooth muscle contraction (8), whereas EP 2 and EP 4 receptors, coupled to the cAMP/ adenylate cyclase pathway, induce relaxation of smooth muscle (8). In the lung, PGE 2 functions as a bronchiolar tone modulator. EP 1 and EP 3 receptors mediate bronchoconstriction indirectly through activation of neuronal pathways (10), whereas bronchodilatation results from direct activation of EP 2 receptors on airway smooth muscles (10 -12). Furthermore, PGE 2 induces SP-A synthesis by human fetal lung explants via the cAMP pathway (13) and phosphatidylcholine secretion via EP 1 receptor in rat cultured alveolar type II cells (14).The first aim of this study was to evaluate the presence and determine cellular localization of EP receptor expression in the fetal baboon lung. Glucocorticoids have been shown to alter PG synthesis and metabolism (15,16); however, no data exist relating to potential alterations in PG receptor-mediated function. To address potential effects of glucocorticoid on PG receptors, we hypothesized that ␤M enhances EP 1 and cAMPcoupled EP (i.e. EP 2 and EP 4 ) receptor expression in the fetal lung. Randomized trials in pregnant women have demonstrated that the major benefit ...

Feto-placental Adaptations to Maternal Obesity in the Baboon

“…Finally, tissues were stained with hematoxylin/methylene green and mounted. Positive and negative controls included slides incubated with and without the primary Ab and sections incubated with pre-immune rabbit serum instead of primary Ab [37]. Quantification was performed at 20× magnification, using Image J (NIH program).…”

“…Tissue slices were randomly selected as described elsewhere [37]. Two slices were processed by fixation in 4% glutaraldehyde, 0.5% formaldehyde in 0.1 M Pepers buffer.…”

“…Density of ER to the syncytiotrophoblast (ST) was calculated by superimposing a series of test points (9 per field of view) in a random orientation on the histological images and counting number of points in ST and ER. The villious amplification factor was calculated as a ratio of number of intersections with MV divided by number of intersections with villous surface [37]. Additionally, diameter and length of MV [39] and ER were calculated.…”

Dose-response effects of betamethasone on maturation of the fetal sheep lung

“…After cDNA synthesis, RNA was removed by incubation with 2 units RNase H at 37° C for 20 min. Quantitative PCR was performed as described previously 11 using an iCycler iQ real-time PCR detection system (Bio-Rad, Hercules, CA). All samples were run in triplicate.…”

Prostaglandins mediate the fetal pulmonary response to intrauterine inflammation

“…This enzyme is functionally coupled to PGHS-2 and is induced by inflammation. PGE 2 signals via membrane-bound G-proteincoupled prostaglandin receptors that have been classified into four subtypes, EP [1][2][3][4] (46). PGE receptors and the principal prostaglandin metabolizing enzyme prostaglandin dehydrogenase (PGDH) are all present in the fetal lung and may mediate normal fetal lung development (10,36,46).…”