Identification of carotid vascular receptors that control adrenal catecholamine secretion in dogs

The role of carotid sinus and thyrocarotid mechanoreceptors in the reflex control of adrenal medullary function was assessed in anesthetized dogs with adrenal vein catheters. Dogs underwent carotid sinus, thyrocarotid junction, combined carotid sinus and thyrocarotid junction, or sham denervation. On the day after surgery, catecholamine secretion was measured after carotid occlusion proximal to the thyrocarotid junction, cervical vagotomy, and repeat carotid occlusion, each separated by 90 min. After combined carotid denervation, baseline norepinephrine secretion was increased, resulting in a decreased epinephrine-to-norepinephrine ratio. Carotid occlusion before vagotomy did not change the secretion of catecholamines or the epinephrine-to-norepinephrine ratio. After sham carotid denervation, acute vagotomy did not affect catecholamine secretion. However, after denervation of the carotid sinus or thyrocarotid junction, vagotomy resulted in small increases in catecholamine secretion without changing the epinephrine-to-norepinephrine ratio; the magnitude of the response was augmented after combined denervation. At 90 min after vagotomy in dogs with intact carotid baroreceptors, carotid occlusion increased adrenal secretion of catecholamines and decreased the epinephrine-to-norepinephrine ratio. After denervation of carotid sinus or thyrocarotid junction receptors, carotid occlusion increased secretion of catecholamines without changing the epinephrine-to-norepinephrine ratio; the response was abolished by combined denervation. These results show that both carotid sinus and thyrocarotid receptors contribute to the adrenomedullary response to carotid occlusion and to acute vagotomy. Also, reduction in the activity of carotid sinus and thyrocarotid junction receptors chronically (by denervation) or acutely (by carotid occlusion) results in preferential secretion of norepinephrine over epinephrine.