EFFECTS OF CLONIDINE ON BLOOD PRESSURE AND HEART RATE RESPONSES TO AN EMOTIONAL STRESS IN THE RAT: A SPECTRAL STUDY

Abstract

SUMMARY: 1. The fluctuations that underlie the spontaneous variability of blood pressure (BP) and heart rate (HR) were investigated in conscious normotensive rats using power spectral analysis.2. Air jet stimulation determined a significant BP rise associated with a tachycardia. This environmental mild stressor amplified the 195–605 mHz oscillations of HR which are under autonomic control. No habituation to this stressor was observed since a second stimulation determined similar responses.3. Clonidine (10 μg/kg, i.v.) prevented the BP rise normally associated with air jet stimulation. In addition, clonidine dramatically reduced the amplitude of BP and HR oscillations in the frequency region of 195–605 mHz.4. It is concluded that a mild emotional stressor elicits in normotensive rats a rise in BP and HR associated with modified spectral profiles reflecting sympathetic hyperactivity. Clonidine minored the effects of stress on BP and HR variability and also prevented BP elevation.