Diuresis from stimulation of left atrial receptors in dogs: further purification of the causative agent from plasma.

Stimulation of atrial receptors by distension of a balloon in the left atrium of anaesthetized dogs results in a reflex diuresis mediated by an unknown humoral agent. This paper reports the further purification from plasma of acetone extracts of the humoral agent which may mediate the diuretic response. Activity of the humoral agent was detected using the Malpighian tubules of Rhodnius prolixus. Gel filtration of the acetone extracts on Sephadex G-25 and G-100, followed by dialysis of the fraction from Sephadex G-100 that contained the humoral agent, showed that the activity of the agent was associated with a high molecular weight fraction (greater than 30000). Acetone extracts of the humoral agent were also shown to be stable to treatment with HCl for 1 h at 25 degrees C. After this acid treatment, gel filtration on Sephadex gels and Bio-Gel P-2 showed that the agent was of low molecular weight (less than 1800). It is concluded that the activity of the humoral agent, as detected by the Malpighian tubule preparation, is associated with a molecule of low molecular weight which may be bound to a larger molecule from which it can be dissociated by acid treatment.