Influence of alpha-chloralose on reflex control of the cardiovascular system in lambs.

Alpha-chloralose is an anesthetic agent sometimes used for experiments in fetal and neonatal cardiovascular physiology. However, its effect on baseline cardiovascular variables and reflex control of the circulatory system has not been determined in young animals. We, therefore, investigated the effect of chloralose on blood pressure, heart rate and baroreflex activity in 12 lambs. Each lamb was anesthetized and a single-lumen catheter was placed in the inferior vena cava and a double-lumen balloon-tipped catheter was placed in the descending aorta. Following recovery from surgery for at least 48 h, blood pressure and heart rate were measured during quiet wakefulness and 30 min following the administration of polyethylene glycol-400 or alpha-chloralose (30, 60 or 90 mg/kg of body weight). Baroreflex activity was assessed by reflex slowing of the heart during an acute increase in blood pressure, produced by inflating the balloon in the descending aorta. Administration of polyethylene glycol-400 alone did not significantly affect blood pressure, heart rate or baroreflex activity. However, alpha-chloralose significantly decreased baroreflex activity in all the doses tested, compared to control responses obtained following the administration of polyethylene glycol-400 alone. Baseline blood pressure and heart rate were increased by 30 and 60 mg/kg of alpha-chloralose, whereas, 90 mg/kg decreased the blood pressure and did not change heart rate. We conclude that alpha-chloralose significantly alters baseline cardiovascular variables as well as reflex circulatory control in lambs. These effects should be taken into consideration when evaluating studies done during alpha-chloralose anesthesia.