Impaired Baroreflex Control of Arterial Pressure in WHHL Rabbits

Abstract

The present study was designed to investigate baroreflex control capacity of arterial pressure (AP) in the conscious Watanabe heritable hyperlipidemic (WHHL) rabbit. The control capacity of the baroreflex system was assessed with overall open-loop gain (G). Seven WHHL and 14 normal Japanese white rabbits were chronically implanted two catheters in the aortic arch through the left subclavian and common carotid arteries. A small amount of blood (2 ml/kg, body weight) was rapidly extracted into a syringe via the left common carotid artery in the conscious state. Mean arterial pressure (MAP) was monitored with a catheter-transducer system through the left subclavian artery. The MAP responses to the rapid hemorrhage were averaged 8 times by a computer. G was calculated as G=ΔAP_I/ΔAP_S-1, where ΔAP_I was an immediate MAP fall after the hemorrhage and ΔAP_s was a steady-state error 1-2 min after the hemorrhage. The values of G in the conscious normal and WHHL rabbits were 7.35±0.24 and 1.91±0.29 (mean ± SE, p<0.01), respectively. To investigate effects of pentobarbital anesthesia on baroreflex system, the hemorrhage experiment was repeated several times under pentobarbital anesthesia (20 mg/kg, i.v.). The values of G in the anesthetized normal and WHHL rabbits were 6.69±0.23 and 1.68±0.34 (mean ± SE, p<0.01), respectively. G in the normal and WHHL rabbits did not show any significant change in the presence and absence of pentobarbital anesthesia (p>0.05). It is concluded that the reduced baroreflex control capacity of AP was partly caused by decreased sensitivity of the baroreceptors due to spread of sclerotic lesions and that pentobarbital anesthesia did not affect overall AP control capacity of the baroreflex system.