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A reflex increase in heart rate from distension of the junction between the superior vena cava and the right atrium.

1. Localized distension of the junction between the superior vena cava and the right atrium without obstructing venous return caused an increase in heart rate.

Effect of destruction of the posterior pituitary on the diuresis from left atrial receptors.

1. In anaesthetized dogs, stimulation of atrial receptors after destruction of the pituitary gland results in a diuresis. This response was not abolished by the administration of bretylium tosylate and was also observed in a surgically denervated kidney. 2. The diuresis is qualitatively similar to that observed in anaesthetized dogs with intact pituitary glands. 3. It is concluded that the diuresis which results from stimulation of the left atrial receptors is mediated by a blood‐borne agent which is not the antidiuretic hormone.

Effect of stimulating right atrial receptors on urine flow in the dog

1. Complex unencapsulated nerve endings (right atrial receptors) have previously been found in the endocardium of the right atrial appendage and the junction between the superior vena cava and the right atrium.

THE EFFECT OF STRETCHING THE SUPERIOR VENA CAVAL-RIGHT ATRIAL JUNCTION ON RIGHT ATRIAL RECEPTORS IN THE DOG

1. Action potentials were recorded from fibres in the right cervical vagus, the receptor endings of which were localized to the endocardial surface of the superior vena caval—right atrial junction.

The effect of distending the atrial appendages on urine flow in the dog

1. Distension of the atrial appendages resulted in a diuresis, an increase in the rate of Na+ excretion and an increase in heart rate.

Atrial receptors and heart rate: the efferent pathway.

1. Stimulation of left atrial receptors by distension of the junctions between the pulmonary veins and the left atrium is known to cause a reflex increase in heart rate. It was suggested that the efferent path of this reflex was solely in the sympathetic nerves to the heart but more recently the existence of a vagal efferent component has been postulated by Albrook, Bennion & Ledsome (1972). 3. The junctions between the pulmonary veins and the levt atrium were distended before and after the administration of I.C.I. 66082 and bretylium tosylate. The response of an increase in heart rate was significantly decreased after the administration of I.C.I. 66082 (5 mg/kg) and abolished after the administration of bretylium tosylate (10 mg/kg). 3. It is concluded that the efferent pathway of the reflex is solely in the sympathetic nerves to the heart.

Depression of the reflex tachycardia from the left atrial receptors by acidaemia

1. The effects are described of an acidaemia, produced either by the inhalation of carbon dioxide or by an intravenous infusion of hydrochloric acid, on the reflex increase in heart rate which results from stimulation of the left atrial receptors in the anaesthetized dog.