Peripheral beta adrenergic blockade modifies airpuff startle-induced heart rate responses

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Research
• Pharmacology

Background:

• Previous studies noted pressor responses to startle stimuli in rats, with variable bradycardia/tachycardia.
• Hypertensive rats showed no bradycardia, and methylatropine unmasked tachycardia, suggesting concurrent autonomic activity.
• Wistar-Kyoto rats from Charles River Laboratories (WKYCR) also lack baseline bradycardia.

Purpose of the Study:

• To determine if WKYCR and spontaneously hypertensive rats from Charles River Laboratories (SHRCR) exhibit parasympathetic activation during stress.
• To investigate the role of beta-adrenoceptors in mediating cardiac responses to stress.

Main Methods:

• WKYCR and SHRCR were pretreated with various beta-adrenoceptor antagonists (propranolol, metoprolol, celiprolol, ICI 118,551).
• Heart rate (HR) and pressor responses to airpuff startle stimuli were measured.
• Effects of beta-blockade on resting HR and stress-induced heart rate changes were analyzed.

Main Results:

• Beta-1 selective agents unmasked bradycardia in both WKYCR and SHRCR, indicating suppressed parasympathetic activity.
• ICI 118,551 (beta-2 antagonist) reduced stress-induced tachycardia in WKYCR, implicating beta-2 adrenoceptors.
• Significant cardiac contributions to pressor responses were observed in both rat models.

Conclusions:

• Parasympathetic activation during stress can be unmasked by blocking sympathetic chronotropic effects.
• Both beta-1 and beta-2 adrenoceptors play distinct roles in mediating cardiac autonomic responses to stress.
• These findings contribute to understanding autonomic dysregulation in cardiovascular conditions.