Collagen in the fetal membranes of sheep: changes throughout gestation and effects of dexamethasone at 60 days

Abstract

The tensile strength of fetal membranes is largely due to their collagen content. In this study we have examined the changes in collagen in the amniotic and allantoic membranes of the sheep over a wide gestational range (27–142 days of gestation; term, 145–150 days). The results have been correlated with volume changes in normal development, and in particular, the changes in allantois have been studied after a rapid and extensive increase in allantoic volume, as a result of maternal dexamethasone treatment (0·76 mg h^-1 for 48 h) from Day 60 of gestation. Electron microscopy and immunohistochemistry were used to delineate collagen distribution, and gel electrophoresis was used to assess the relative proportions of each type. In the amnion, collagen content increased from 37±4% to 50±1% dry weight of the tissue from 41–102 days and declined slightly thereafter. In the allantois, collagen content increased from 20±1% at Day 27 to 50±6% at Day 142, significantly correlated with a volume increase from 253 mL to 813±274 mL. Collagen types I (>85%), III (10%) and small amounts of types IV and V (<5%) were identified in both membranes at all ages. When allantoic fluid volume was increased rapidly by maternal dexamethasone infusion, there was a significant decrease in collagen content from 38±6% to 25±2% (P < 0·05). By immunohistochemistry it was observed that both epithelial cells and fibroblasts were synthesizing collagen.