Role of the sympathicoadrenal system in the hemodynamic response to exercise in dogs

Twelve dogs that ran well on a motor-driven treadmill were vagotomized and sympathectomized from TI-TT plus LB-L6 and subjected to either unilateral adrenalectomy and contralateral adrenal demedullation (W-A) or denervation of cranial mesenteric and common hepatic arteries (SN-MH). After recovery, cardiac output determinations (direct Fick) and continuous recording of mean aortic blood pressure, heart rate, and oxygen consumption were made at rest and during exercise at 7.5 km/hr- 10% gradient Heart rate increased from 113 to 126 beats/min in the medulloadrenalectomized dogs and from 98 to 147 beats/min in dogs with hepatomesenteric denervation. Mean blood pressure did not vary substantially with exercise in either series of animals, averaging at rest 89 mm Hg in dogs with adrenal medullectomy and 128 mm Hg in dogs with intact adrenals. The resting cardiac index was similar in both groups (2.61 liters/min per m2) and increased about 200 y0 during exercise in medulloadrenalectomized animals as compared with 330y0 in dogs with hepatomesenteric denervation. During exercise, energy cost was essentially similar although peripheral resistance decreased about 75y0 in both groups.