Baroreceptor reflexes in postural control of circulation in rabbits.

The present study was undertaken to evaluate reflex cardiovascular responses to postural stress in rabbits. The changes in mean arterial pressure (MAP) and heart rate (HR) were monitored in the supine position and following sudden passive head up tilt (HUT), and head down tilt (HDT) to 70 degrees. The results show a significant increase in MAP (18.57%, P less than 0.001) and HR (2.92%, P less than 0.02) with HUT; and a marked decrease in MAP (43.48%, P less than 0.001) and HR (8.21%, P less than 0.001) with HDT (as compared to the values in supine position). The changes in MAP were found to be more marked than those in HR. The depressor responses to HDT were more marked than the pressor responses to HUT.