The renal clearance and plasma binding of vasopressin in the dog

The isolated dog kidney was perfused with blood containing 1 m-u. arginine vasopressin/ml. In other experiments 40 or 50 m-u./min. were infused into three intact dogs. Antidiuretic activity was measured in renal venous blood, arterial blood, and in the urine. Renal blood flow was determined directly in the perfused dog kidney and by p-aminohippuric acid clearance in the intact dog; glomerular filtration rate was measured by either inulin or creatinine clearance.

About 38% of the hormone was extracted from the arterial blood in its passage through the kidney. Of the total amount of hormone infused, about 18% was eliminated by each kidney. The quantity of vasopressin extracted from the blood was greater than that excreted in the urine, indicating that the hormone is inactivated by the kidney. In intact dogs, the amount of hormone filtered by the kidney was less than that excreted, suggesting tubular secretion.

It was calculated that the release of endogenous arginine vasopressin induced by the stimuli of anaesthesia and surgery was between 3 and 7 m-u./min. and that approximately 15% of the endogenous hormone was excreted.

Ultrafiltration of dog plasma at three different concentrations of arginine vasopressin (30, 100 and 290 μ-u./ml.) showed that binding was reduced as the concentration was raised and that at the concentration of hormone in the experiments, less than 30% was bound.

The difficulties of relating these findings at artificially high blood concentrations to those at physiological blood concentrations of vasopressin are discussed.

The value of rats with hereditary hypothalamic diabetes insipidus for the bioassay of vasopressin

The pituitary glands of 11 rats (six females and five males, weighing 140–200g.) with hereditary hypothalamic diabetes insipidus (DI) were found to contain oxytocin but no vasopressin.

The DI rats could not always be distinguished from rats without diabetes insipidus (non-diabetes insipidus, NDI rats) by measurement of their daily urine volume.

Stimulation of the neurohypophysis by fall in arterial pressure (haemorrhage, methacholine) or by nicotine, released vasopressin in NDI rats to produce a sustained antidiuresis, but in the DI rats there was only a transient fall in urine flow which did not outlast the hypotension.

The DI rats were about twice as sensitive to vasopressin as NDI rats. As assay preparations they have the advantage that they cannot respond to vasopressin-releasing stimuli.

Prolonged administration of Pitressin tannate in oil increased maximum urinary osmolality in DI rats, but failed to increase their sensitivity to intravenously injected vasopressin.