AJP - Regulatory, Integrative and Comparative Physiology, Vol 240, Issue 3 235-R245, Copyright © 1981 by American Physiological Society
Factors affecting 3H2O transfer capacity of isolated perfused trout gills
W. F. Jackson and P. O. Fromm
Tritiated water (3H2O) transfer capacity (PdA) and vascular impedance (Zg)
of isolated trout (Salmo gairdneri) gills perfused with or without
epinephrine were studied under conditions of altered osmotic gradients,
fluid stirring, perfusion rate (Qa), and efferent pressure (Pe). Transfer
capacity was unaffected by osmotic gradients, indicating that 3H2O moves
across gills by diffusion and that PdA is independent of hydraulic water
movement. Fluid stirring increased PdA asymptotically, suggesting that
boundary layers significantly affect diffusion across isolated gills.
Transfer capacity was directly related to Qa; Zg was inversely related to
Qa. The PdA results can be explained in terms of lamellar recruitment and
the distribution of flow between secondary lamellae. Increased Qa reduced
Zg due to recruitment and distension of gill vessels. Elevated Pe decreased
Zg and PdA. The effects of Pe on Zg resulted from distension of the gill
vasculature and increased venous drainage, whereas the effects of Pe on PdA
can be explained by changes in the distribution of perfusion between
secondary lamellae.
