Objectives: The Bezold-Jarisch reflex involves a marked increase in vagal (parasympathetic) efferent discharge to the heart. During micturition, there is a marked increase in parasympathetic activity to the bladder (pelvic nerve activity) and this coincides with periods of phasic bladder contractions. In recent studies, we have shown that regions of the CNS that modulate pelvic nerve activity also affect cardiovascular variables. Recent anatomical studies have shown neuronal connections between the areas of the CNS that modulate both reflexes. Accordingly, in the present study we investigate if during the Bezold-Jarisch reflex there are simultaneous changes in pelvic nerve activity.
Methods: Experiments were performed in Wistar female rats, anaesthetised with alpha-chloradose i.p. (80 micrograms/Kg) supplemented i.v. as required. Arterial blood pressure, ECG heart rate, urinary bladder pressure and pelvic nerve activity were recorded.
Results: Stimulation of cardiac chemosensitive nerve endings with veratridine evoked a decrease in arterial blood pressure from 88.6 +/- 1.72 to 66.1 +/- 2.50 mmHg (n = 30; p < 0.0001) and of heart rate from 420.3 +/- 5.56 to 248.8 +/- 17.58 bpm (n = 13; p < 0.0001) There were simultaneous changes of pelvic nerve activity that preceded an increase in urinary bladder pressure from 10.2 +/- 0.28 to 26.3 +/- 1.52 cmH2O (n = 30; p < 0.0001) and bladder contractions. We believe that the reflex changes resulted from activation of cardiac chemosensory nerve endings, as equivalent injections of warm saline into the left ventricle produced no changes in either cardiovascular variables or pelvic nerve activity.
Conclusions: These observations suggest a significant role for cardiac afferents in modulating bladder contractions. The integration and functional significance of these inputs remain to be elucidated. The clinical importance of this physiological result may contribute to a better understanding of the mechanism of some semiologic findings, notably the association of urgency to micturate with myocardial ischemia and myocardial infarction.