The role of the heart in body fluid and electrolyte homeostasis.

Inflation of a balloon at the right superior vena caval/right atrial junction of the rat causes no change in arterial or venous blood pressure but does attenuate spontaneous night-time drinking and the acute responses to 24 h water deprivation and s.c. isoprenaline. Water intake after i.p. hyperoncotic colloid is virtually abolished whereas there is no effect on drinking to i.v. hypertonic saline or intracerebroventricular angiotensin II. Inflating the balloon also results in diuresis and natriuresis even in the conscious, renally denervated, Brattleboro' rat. Under these conditions the change in urine output cannot be explained by a fall in nervous input to the kidney, nor can it be caused by decreased ADH release since the Brattleboro' rat is totally deficient in ADH. Since there is no change in blood pressure, the diuresis and natriuresis must be mediated by some, as yet uncharacterized, hormonal factor. It is concluded that stimulation of the right atrial receptors resulting from increased venous return to the heart does play a role in controlling fluid intake and output and that this may be mediated at least in part, by a factor released from the heart itself.