Vagal and sinoaortic reflexes in postural control of circulation and renin release

Anesthetized cats were subjected to two 10-min trials of head-up tilting spaced 60 min apart. Bilateral cervical vagotomy, performed after the first tilting episode, did not affect the hemodynamic response to the change in posture, but significantyly and markedly reduced the increase in renin release from the innervated kidney. After sinoaortic denervation a marked and sustained arterial hypotension occurred during tilting, and the postural increase in renin release, though still limited to the innervated kidney, was even greater. When pressure homeostasis to tilting was disturbed, the renin release response was seen to be independent of the vagi, as it occurred after combined vagotomy and sinoaortic denervation. Maintenance of arterial pressure during tilting is mainly due to sinoaortic reflexes, whereas vagal reflexes are mostly responsible for the postural increase in renin release. The vagally independent release of renin observed when the cardiovascular response to tilting is impaired, is probably due to a direct action of arterial hypotension on intrarenal receptors, an action occurring only in innervated kidneys.