Baroreceptor reflex effects on transient and steady-state hemodynamics of salt-loading hypertension in dogs

Intact dogs were compared with barorecptor-denervated dogs to determine the extent to which the baroreceptor reflexes delay the onset and offset transients and alter the final steady-state levels of salt-loading hypertension. Two months after their renal mass had been reduced to about one-third of normal, hypertension was produced in both groups of dogs by continuous intravenous infusion of isotonic saline (190 ml/kg day-1). Major hemodynamic variables were recorded continuously 24 hours/day throughout the experimental period. Both groups of dogs had similar control 24-hour arterial blood pressure values: intact dogs averaged 112 plus or minus 4.1 (SE) mm Hg, and denervated dogs averaged 110 plus or minus 4.3 mm Hg. Both groups reached the same average plateau of elevated arterial blood pressure: intact dogs averaged 142 plus or minus 4.8 mm Hg, and denervated dogs averaged 142 plus or minus 8.7 mm Hg. After the start of salt loading, the denervated dogs reached their plateau level of arterial blood pressure in an average of 8 hours compared with nearly 24 hours for the intact dogs. Cardiac output also rose more rapidly in the denervated dogs and reached a maximum elevation of 26% above the control level in an average of 7.4 hours compared with a maximum elevation of 40% above control in the intact dogs in 18 hours. Total peripheral resistance fell below the control level during the entire first day of infusion in the intact dogs but was somewhat elevated in the denervated dogs. When the saline infusion stopped, arterial blood pressure in both groups returned to control levels within 24 hours. The results indicate that the major action of the baroreceptor reflexes on the onset of salt-loading hypertension is to slow the development of hypertension by modifying the total peripheral resistance; the final steady-state level of hypertension is unaffected by the baroreceptor reflexes.