Recovery of peripheral chemoreceptor function after denervation in ponies

Abstract

Resting ventilation (PaCO2) and ventilatory responses to acute hypoxia and to intravenous NaCN were assessed over a 4-yr period following cutting of the carotid sinus nerves and stripping the adventitia of the aortic arch. The data indicated essentially complete loss of peripheral chemoreceptor function immediately after surgery and hypoventilation during normoxia (delta PaCO2 = +8.7 Torr). There was a time-dependent, partial recovery of peripheral chemoreceptor function between 2 and 22 mo after surgery. Approximately 10% of the ventilatory response to iv NaCN returned, and 30-40% of the normal response to acute hypoxia was restored. Resting PaCO2 was no longer significantly elevated above normal by 22 mo after surgery. Four years after surgery these animals were unable to sustain normal ventilatory acclimatization to chronic hypoxia just as in an earlier study in the same ponies. Experiments carried out under anesthesia showed that recovered peripheral chemoreceptor sensitivity was not present in the carotid chemoreceptor area. However, sectioning of the aortic nerve caused the animals to again hypoventilate during acute hypoxia, and it nearly eliminated the ventilatory response to NaCN, but normal eucapnic ventilation was retained. We conclude that in the pony aortic chemoreceptors become functional in a time-dependent manner following carotid body denervation.