Renal Function in the European Eel ( Anguilla Anguilla L.): Effects of the Caudal Neurosecretory System, Corpuscles of Stannius, Neurohypophysial Peptides and Vasoactive Substances

SUMMARY Removal of the caudal neurosecretory system from freshwater eels did not affect urine flow or urinary Na excretion. There was, however, a marked initial increase in K, Ca and Mg excretion which later declined to very low levels by the 4th day after operation. Intravenous injection of saline extracts of Mugil or Anguilla urophyses elicited a rise in urine flow and inulin clearance rates. This response was correlated with rises in blood pressure in the dorsal aorta. Urinary Na concentration also increased. Injection of saline extracts of corpuscles of Stannius at the dose of two glands/kg. body weight generally caused an initial decline in inulin clearance rates while urine volume increased. Smaller doses caused the reduction of inulin clearance rates only. Isotocin, amongst the neurohypophysial peptides, was the most effective in causing a diuresis and increases in p-aminohippuric acid and inulin clearance rates. There was little or no change in urinary Na concentration. Oxytocin and arginine vasotocin were effective but less potent. Arginine or lysine vasopressin had no effect even at large doses. Angiotensin II and adrenaline induced diuresis and natriuresis followed occasionally by a transient antidiuresis.