Oxygen transfer, gill resistance and structural changes in rainbow trout (Salmo gairdneri, Richardson) gills perfused with vasoactive agents.

1. Gill resistance (Rg) and oxygen transfer (To2) were measured in perfused rainbow trout gills. After perfusion the gills were analysed morphometrically. 2. Rg increased with 40% and To2 decreased with 91% during 60 min perfusion without vasoactive substances in the perfusion Ringer. 3. In presence of 10 micro M adrenaline both Rg and To2 remained stable at their starting levels throughout the experimental period (60 min). 4. With 0.2 micro M acetylcholine and 10 micro M adrenaline in Ringer Rg increased nearby to the same extent as in perfusions without vasoactive agents, while To2 was not significantly affected. 1 micro M acetylcholine increased Rg with 76% and decreased To2 with 51%. 5. The changes in Rg and To2 could be explained by structural changes in the secondary lamellae.