An attempt to quantitate the contribution of antidiuretic hormone to the diuresis of left atrial distension in conscious dogs.

In order to quantitate the contribution of the antidiuretic hormone (ADH) to the diuresis of left atrial distension 52 experiments have been performed in 12 conscious, chronically instrumented beagle dogs. Left atrial pressure was increased by a reversible mitral stenosis by about 10 cm H2O (1.0 kPa) for 60 min. Plasma ADH concentration (range between 1.3 and 6.0 pg . ml-1) (radioimmunoassay) decreased in every experiment, the average decrease being about 50%. An i.v. infusion of vasopressin (0.05 mU . min-1 . kg-1) abolished the diuretic effect of left atrial distension or decreased the urine volume below control values; natriuresis was not affected. The magnitude of the vasopressin effect was dependent on the concurrent sodium excretion: when sodium excretion was low during left atrial distension, vasopressin was more effective in reducing the urine volume than when sodium excretion was high. It is concluded that the diuresis of left atrial distension is mediated (a) by a suppression of ADH and (b) by factors controlling sodium excretion, the contribution of these two mechanisms being dependent on the concurrent sodium excretion.