title: Early postnatal dexamethasone diminishes transforming growth factor alpha localization within the ileal muscularis propria of newborn mice and extremely low-birth-weight infants.
abstract: Focal small bowel perforation (FSBP) occurs most commonly in the ileum of extremely low-birth-weight (ELBW) infants. Early postnatal dexamethasone (EPD) administration results in an increased risk for FSBP in this patient population, but the mechanism by which this occurs is unknown. Infants with FSBP have healthy mucosa but thinned smooth muscle, suggesting a mechanism involving the muscularis propria for these perforations. One explanation for these findings would be that dexamethasone alters the tissue availability of pertinent growth factors to the smooth muscle. To explore this possibility, we administered dexamethasone or saline by intraperitoneal injection to newborn mice for 3 days (dosed at 1 microg/g of body weight/day) to simulate EPD protocols. The animals were sacrificed after 72 h of treatment and their ileums harvested and prepared for microscopy. Immunolocalization was performed for three related growth factors (epidermal growth factor [EGF], heparin-binding EGF [h-EGF], and transforming growth factor alpha [TGF-alpha]) and their common receptor. We found TGF-alpha to be abundant and discretely localized in the muscularis propria in control animals but to be diminished in dexamethasone-treated animals. EGF-receptor immunostaining was also decreased with dexamethasone but there was minimal to no detection of EGF or h-EGF in either treatment condition. Surgical and autopsy specimens of the ileum were obtained from seven ELBW infants who either received EPD or not. These tissues were used for immunolocalization of the same growth factors and similar distributions for TGF-alpha were observed in several of these cases. These findings are consistent with an autocrine role for TGF-alpha in ileal smooth muscle proliferation and suggest a mechanism by which EPD might mediate smooth muscle thinning.
authors.affiliation: Department of Pediatrics, Division of Neonatology, University of Virginia Health System, P.O. Box 800386, Charlottesville, VA 22908, USA.
authors.forename: P V
authors.initials: PV
authors.lastname: Gordon
authors.forename: W A
authors.initials: WA
authors.lastname: Price
authors.forename: A D
authors.initials: AD
authors.lastname: Stiles
authors.forename: J C
authors.initials: JC
authors.lastname: Rutledge
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology*; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D007082:Ileum / Q000187:drug effects* / Q000378:metabolism; D007124:Immunoenzyme Techniques; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight / Q000378:metabolism*; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D016211:Transforming Growth Factor alpha / Q000378:metabolism*
chemical_list: C587883:HBEGF protein, human; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D016211:Transforming Growth Factor alpha; D004815:Epidermal Growth Factor; D003907:Dexamethasone; D066246:ErbB Receptors