Vasopressin prolongs bradycardiac response during orientation

Area of Science:

• Neuroendocrinology
• Cardiovascular Physiology
• Behavioral Neuroscience

Background:

• The orienting response (OR) is a fundamental reaction to stimulus change.
• The cardiovascular component of the OR, particularly heart rate changes, is well-documented.
• The role of neurohypophyseal peptides in modulating the OR's cardiovascular aspects requires further elucidation.

Purpose of the Study:

• To investigate the effects of arginine vasopressin (AVP) and oxytocin on the cardiovascular response to stimulus offset.
• To determine if these neurohypophyseal hormones influence the orienting response (OR) in adult male rats.

Main Methods:

• Adult male rats were instrumented with ECG electrodes.
• Electrocardiogram (ECG) was recorded during habituation to a dark chamber with background noise.
• ECG was measured before, immediately after, and 3 minutes post-stimulus offset (noise elimination).
• Rats received subcutaneous injections of AVP or oxytocin (1 microgram/rat) 1 hour prior to testing.

Main Results:

• Sudden elimination of background noise elicited a transient bradycardia, indicative of an orienting response.
• Neither AVP nor oxytocin altered baseline heart rate or the immediate bradycardiac response to stimulus offset.
• AVP, and to a lesser extent oxytocin, significantly prolonged the duration of the stimulus-offset-induced bradycardia.

Conclusions:

• Neurohypophyseal peptide hormones, AVP and oxytocin, modulate the cardiovascular component of the orienting response.
• These hormones do not affect the onset of bradycardia but extend its duration following stimulus offset.
• Findings suggest that AVP and oxytocin enhance the cardiovascular adaptation to environmental change.