Cardiac parasympathetic hyperresponsiveness in spontaneously hypertensive rats

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System
• Hypertension Research

Background:

• Hypertension is associated with impaired baroreceptor function and reduced cardiac autonomic responsiveness.
• The vagus nerve plays a key role in the bradycardic response to baroreceptor stimulation.
• Existing research suggests reduced cardiac parasympathetic responsiveness in hypertension.

Purpose of the Study:

• To investigate cardiac parasympathetic responsiveness in spontaneously hypertensive rats (SHRs) compared to normotensive Wistar-Kyoto (WKY) rats.
• To determine if reduced parasympathetic responsiveness is a feature of established hypertension.
• To examine the age-dependent onset of alterations in cardiac parasympathetic responsiveness in hypertension.

Main Methods:

• Used 8- and 12-week-old SHRs and WKY rats.
• Assessed cardiac parasympathetic responsiveness via vagal nerve stimulation (1-16 Hz) and methacholine injections (1-8 µg/kg).
• Measured bradycardia as the response to graded stimulation and calculated responsiveness from the regression slope.

Main Results:

• 12-week-old SHRs exhibited significantly greater cardiac parasympathetic responsiveness to both vagal stimulation and methacholine compared to age-matched WKY rats.
• No significant differences in cardiac parasympathetic responsiveness were observed between 8-week-old SHRs and WKY rats.
• These findings contrast with the hypothesis of reduced parasympathetic responsiveness in hypertension.

Conclusions:

• Cardiac parasympathetic responsiveness is paradoxically enhanced, not reduced, in 12-week-old spontaneously hypertensive rats.
• Alterations in cardiac parasympathetic responsiveness in hypertension appear to develop with age.
• Further research is needed to elucidate the mechanisms behind this age-dependent enhancement in hypertensive rats.