The Cardiovascular Effects of Coronary Sinus Distension in the Anaesthetised Dog

Experiments were carried out to determine whether the systemic hypotension caused by distension of the coronary sinus is reflex in origin. In anaesthetized open‐chest dogs, indwelling Morawitz balloon cannulae were used to distend the sinus. Eighty‐three distensions in fourteen experiments with intact vagi caused systemic hypotension and tachyeardia, but there was no significant change in this response in a further twenty‐two tests after the cervical vagi had been cut, or cooled (to less than 5°C). Recordings were made of sympathetic efferent nerve activity in few‐fibre preparations from the ventral ansae subelaviae. Activity was reduced during the hypotension reflexly caused by intrapericardial nicotine but was increased after coronary sinus distension. The increase in activity occurred both with intact and sectioned vagi. It was concluded that the excitation of cardiac mechanoreceptors in the coronary sinus wall by distension does not produce measurable reflex depression of the circulation, and that the hypotension observed after sinus distension is mechanically caused, rather than reflex in origin as earlier studies have implied.