Cardiac parasympathetic hyperresponsiveness in spontaneously hypertensive rats

Alberto U. Ferrari, Anna Daffonchio, Cristina Franzelli, Giuseppe Mancia

Research output: Contribution to journalArticlepeer-review


The bradycardic response to baroreceptor stimulation is impaired in human and experimental hypertension. Because this bradycardia mainly depends on the vagus, this may reflect a reduced cardiac parasympathetic responsiveness, which would parallel the reduced cardiac adrenergic responsiveness observed in hypertension. To test this hypothesis, 12-week-old spontaneously hypertensive rats (n = 12) and normotensive Wistar-Kyoto rats (n = 11) were anesthetized with ketamine and underwent bilateral vagotomy. Cardiac parasympathetic responsiveness was assessed from the bradycardia induced by 1) graded electrical stimulation of the right efferent vagus (1–16 Hz) and 2) graded intravenous injections of methacholine (1–8 μg · kg−1). The slope of the linear regression between the bradycardic response and the applied stimulus was taken as the measure of cardiac parasympathetic responsiveness. To identify the onset of possible alterations in cardiac parasympathetic responsiveness in hypertension, the study was extended to younger (8-week-old) spontaneously hypertensive (n = 11) and Wistar-Kyoto (n = 13) rats. With vagal stimulation, cardiac parasympathetic responsiveness was greater in 12-week-old spontaneously hypertensive rats than in 12-week-old Wistar-Kyoto rats (24.8±5.4 versus 10.1±1.2 beats per minute per hertz, mean±SEM, p <0.035). This was also the case with methacholine (18.8±3.5 versus 13.1±4.4 beats per minute per microgram per kilogram, p <0.045). In contrast, cardiac parasympathetic responsiveness was similar, with both vagal stimulation and methacholine, when tested in the younger spontaneously hypertensive and Wistar-Kyoto groups. Thus, in established (but not in early) hypertension cardiac parasympathetic responsiveness is not reduced but rather augmented, suggesting that factors other than an end-organ responsiveness are responsible for the impaired baroreceptor-heart rate reflex. The enhanced cardiac parasympathetic responsiveness in spontaneously hypertensive rats may be due to upregulation of cardiac muscarinic receptors in response to the chronically reduced vagal tone that characterizes hypertension.

Original languageEnglish
Pages (from-to)653-657
Number of pages5
Issue number6
Publication statusPublished - 1992


  • Baroreceptor reflexes
  • Methacholine chloride
  • Receptors, muscarinic
  • Sinoatrial node
  • Spontaneously hypertensive rats
  • Vagus nerve

ASJC Scopus subject areas

  • Internal Medicine


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