Response of air sac mesothelium to expansion of extracellular fluid volumein Gallus domesticus

In this study, scanning electron microscopy was used to examine the effects of hydrothorax on the morphology of the air sac visceral mesothelium of Ga llus domesticus. Anaesthetized chickens were subjected to acute hydrodynami c pulmonary oedema induced by expansion of the extracellular fluid volume w ith an infusion of Ringer's solution equal to 6.5% of body weight. Tissue s amples from the visceral surface of the abdominal air sacs near their ostia were obtained and fixed after death induced by anaesthetic overdose. These were compared with similar samples from control "non-volume-loaded" birds. The air sac visceral mesothelium of the volume-loaded animals presented an increased density of bulbous or swollen microvilli. These deformations wer e similar to changes reported in the visceral pleura of mammals subjected t o hydrothorax, suggesting a commonality with regard to the role of these me sothelia in liquid clearance during pulmonary oedema. (C) 2000 Harcourt Pub lishers Ltd.