Mechanism of diuretic response to increased left atrial pressure in the anesthetized dog

Abstract

The mechanism whereby an increase in left atrial pressure (LAP) causes a water diuresis in the anesthetized dog remains controversial. In the present study LAP was increased by inflation of an atrial balloon in two groups of animals. In the first group of eight intact dogs, mean LAP was increased from 3.4 to 17.6 mm Hg (P less than 0.001). The rise in LAP was associated with a mean increase in urine flow (V) from 0.70 to 1.29 ml/min (P less than 0.001), a decrease in urinary osmolality (Uosm) from 808 to 490 mOsm/kg of H2O (P less than 0.001) and an increase in free water clearance (CH2O) from -0.684 to -0.200 ml/min (P less than 0.025). This diuresis was associated with a mean decrease in antidiuretic hormone concentrations in plasma as measured by radioimmunoassay from 27.6 to 12.3 pg/ml (P less than 0.02). The changes in the urinary indexes and in the antidiuretic hormone concentrations were reversible and returned to control levels when the LAP was allowed to return to normal. A second group of dogs was acutely hypophysectomized, steroid replaced and given a constant infusion of vasopressin. In these animals, mean LAP was increased from 3.0 to 16.0 mm Hg (P less than 0.001) but no significant change in V (0.49 to 0.56 ml/min), Uosm (878 to 845 mOsm/kg of H2O) or CH2O (-0.750 to -0.620 ml/min) occurred. Cardiac output, renal arterial pressure, glomerular filtration rate and solute excretion were comparable in the two groups. We therefore conclude that suppression of antidiuretic hormone release is the primary mechanism whereby increased LAP causes a water diuresis in the anesthetized dog.

A Highly Sensitive and Rapid Radioimmunoassay for the Determination of Argmine8-Vasopressin

“…The present assay can therefore be considered as both highly sensitive, and more rapid than other assays. Isoosmotic arginine 8 -vasopressin suppression by central volume stimulation during water immersion (30,31) was clearly demonstrated in accordance with the findings of other groups, supporting the concept of inhibition of arginine 8 -vasopressin secretion by acute atrial distension (32,33).…”

Plasma vasopressin concentration in the anaesthetized dog before, during and after atrial distension.

“…The majority of previous investigators examining the effects of atrial distension on plasma AVP in anaesthetized dogs (Baisset & Montastruc, 1959;Share, 1965; Shu'ayb et al 1965;Johnson et al 1969;Brennan et al 1971;de Torrente et al 1975) found pre-distension plasma AVP concentrations to be higher than the range of 1-5-6 pg/ml. (Bie, 1980) reported in 'normal' conditions in well hydrated, unanaesthetized, unstressed dogs and other mammals.…”

“…Kappagoda, Linden, Snow & Whitaker (1974) were unable to demonstrate such changes with the bioassay procedure they used. More recently measurements of plasma vasopressin concentration by radioimmunoassay (de Torrente, Robertson, McDonald & Schrier, 1975;Zucker, Share & Gilmore, 1979) have confirmed that plasma vasopressin decreases during atrial distension.…”

Role of Plasma Vasopressin in Impaired Water Excretion of Glucocorticoid Deficiency

“…In addition to nicotine (25), these stimuli include systemic alpha (30) and beta (31) adrenergic stimulation, acute constriction of the thoracic inferior vena cava (32), left atrial distention (33), atrial tachycardia (34), and hypoxia (35). From these results has emerged the hypothesis that the nonosmotic release of vasopressin may have evolved as an integral part of the alarm reaction (36).…”