Natriuretic Effect of Posterior Pituitary Neurophysin

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Abstract
Neurophysins are peptides which are present in the neurohypophysis in association with oxytocin and vasopressin. Two neurophysins, I and II, have been isolated from bovine posterior pituitary powder. Neurophysin I intravenously administered to hydropenic dogs caused a significant (p < 0.001) increase in sodium excretion from 2.3 ± 0.3 μEq/min to 17.3 ± 3.8 μEq/min (mean ± sem). The peak natriuretic response occurred 90–120 minutes after injection of a bolus of neurophysin. Proximal renal tubule recollection micropuncture showed the basal tubular fluid/plasma inulin ratio (TF/P) of 1.50 ± 0.14 decreased significantly (p < 0.05) to 1.22 ± 0.06 (mean ± sem), after injection of neurophysin I. The decreased TF/P indicated a decrease in the fractional sodium reabsorption in the proximal tubule. Neurophysin II caused no change in urinary excretion. A biochemically specific posterior pituitary peptide has been demonstrated to have natriuretic activity in the dog. At least part of this action is due to an effect on the proximal renal tubule. This indicates that neurophysins may be biologically active peptides rather than just “carrier proteins.”

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