Abolition of atrial receptor diuresis and of release of humoral agent by cooling the vagal nerves.

Stimulation of atrial receptors in anaesthetized dogs results in a reflex increase in urine flow mediated by vagal myelinated fibres and, in part, by a humoral agent of unknown identity. The humoral agent has been detected by an in vitro preparation of the Malpighian tubules of Rhodnius prolixus. The purpose of this investigation was to determine whether the present extract of plasma purporting to contain the humoral agent is also related to the reflex diuresis. In nine chloralose anaesthetized dogs atrial receptors were stimulated by distension of a balloon in the left atrium. Plasma samples collected before and during distension of the balloon, respectively, were precipitated with acetone, acid-treated and fractionated on Bio-Gel P-2. The purified samples were tested for the activity of the humoral agent on the Malpighian tubule preparation. In each dog, distensions of the balloon were performed with the cervical vagal nerves at 9 and 37 degrees C. Cooling the vagal nerves to 9 degrees C abolished the reflex diuresis and abolished the activity of the humoral agent recovered from a Bio-Gel P-2 fraction (molecular weight range 100-1800) which elutes between the void volume and the salt fraction. It was concluded that the substance recovered from Bio-Gel P-2 is associated with the diuresis in response to stimulation of atrial receptors; it is suggested that its presence is dependent on the integrity of the afferent limb of the atrial receptor reflex.