Effect of atherosclerosis on the responsiveness of the rapidly acting arterial pressure control system in WHHL rabbits

The open loop gain of the rapidly acting arterial pressure control system was estimated in 15 Watanabe heritable hyperlipidaemic (WHHL) rabbits aged 3-31 months. Twenty five normal Japanese white rabbits, aged 6-30 months, were used as controls. After being anaesthetised by an intravenous injection of pentobarbital sodium, the rabbits were bled by 2 ml X kg-1 body weight within 1-2 s through a catheter inserted into the aortic arch. The arterial pressure change after this rapid haemorrhage was recorded for more than 2 min by a catheter placed in the aortic arch. The open loop gain was calculated as (delta API/delta APS)-1, where delta API was the immediate fall and delta APS the steady state fall. The pulse pressure, delta API, and delta APS increased and the open loop gain decreased with age in the WHHL rabbits, but the mean arterial pressure did not change significantly with age. After aortic denervation the open loop gain also decreased with age in the WHHL rabbits. These results indicate that the progress of atherosclerosis with aging in the Watanabe heritable hyperlipidaemic rabbit decreases the vascular compliance and impairs the arterial pressure restoring function of the rapidly acting arterial pressure control system.