The effect of stimulation of the atrial receptors on plasma cortisol level in the dog.

1. Experiments were performed in dogs anaesthetized with alpha-chloralose to determine whether stimulation of atrial receptors reflexly results in a consistent change in plasma cortisol levels. Either a large balloon in the lumen of the left atrium or small balloons positioned at the upper and middle pulmonary vein-atrial junctions and atrial appendage were distended. Plasma samples obtained from these dogs during control periods and during periods of stimulation were assayed for plasma cortisol level. 2. Initially, stimulation of left atrial receptors by either large or small balloon distension was shown consistently to cause the responses of an increase in urine flow and a decrease in plasma cortisol level. The responses were greater during stimulation using the large balloon than the small balloons. 3. The afferent limb of the responses was shown to involve the vagal nerves. Cooling of the cervical vagosympathetic nerve trunks to 9 degrees C abolished the responses to balloon distension of an increase in urine flow and decrease in the level of plasma cortisol. 4. The efferent limb of the cortisol response was shown to require the pituitary gland. Hypophysectomy abolished the response of a decrease in plasma cortisol level, but not the diuretic response. 5. It was shown that stimulation of left atrial receptors causes a reflex decrease in plasma cortisol level, the afferent limb of which involved vagal nerves and the efferent limb of which depended on the pituitary gland.