Response of air sac mesothelium to expansion of extracellular fluid volume in 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 Gallus domesticus. Anaesthetized chickens were subjected to acute hydrodynamic pulmonary oedema induced by expansion of the extracellular fluid volume with an infusion of Ringer's solution equal to 6.5% of body weight. Tissue samples 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 were similar to changes reported in the visceral pleura of mammals subjected to hydrothorax, suggesting a commonality with regard to the role of these mesothelia in liquid clearance during pulmonary oedema.