Control of renal functions in lungfishes.

Lungfishes are freshwater fishes related to the ancestors of the early amphibians. Although lungfishes have many amphibian-like characteristics, their renal functions closely resemble those of other freshwater fishes. There is no evidence suggesting that tubular reabsorption of water is under physiological control, and glomerular filtration rate (GFR) appears to determine urine flow and water excretion, GFR responds to changes in blood pressure. Arginine vasotocin (AVT) is a potent vasopressor and diuretic agent in lungfishes. If AVT is actually a hormone in fishes, its primary actions may be vasopressor, and the effects of exogenous AVT on GFR and urine flow may represent a pharmacological response to elevated renal perfusion pressure. AVT does not seem to have hydroosmotic effects on either skin or renal tubules in lungfishes, as it does among amphibians.