Effects of restraint on baroreflex sensitivity in altering heart rate and heat production in rats

When systemic arterial pressure was elevated with phenylephrine (PHE) at 13 degrees C, heart rate (HR), and heat production (M) associated with shivering were greatly suppressed in rats. The magnitude of suppression increased proportionally with increasing doses of PHE. During restraint, however, such a suppression of HR and M with PHE was attenuated, indicating that restraint reduced baroreflex sensitivity in altering HR and shivering in rats.