Why the study?
Does adrenaline combined with vagal stimulation affect cerebral blood flow differently than vagal stimulation alone in an experimental cat model of vasovagal reflex?
Does adrenaline combined with vagal stimulation affect cerebral blood flow differently than vagal stimulation alone in an experimental cat model of vasovagal reflex?
In a cat model, adrenaline combined with vagal stimulation reduced cerebral blood flow more than vagal stimulation alone, suggesting accentuated antagonism during vasovagal reflex.
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May suggest accentuated antagonism in feline vasovagal models; leaves open human relevance for cerebral perfusion.
IntroductionThe vasovagal reflex causes spontaneous dizziness which appears in a standing or sitting position. This reaction is probably caused by the autonomic reflex. It has long been recognized that the plasma adrenaline (Adr.) level elevates during vasovagal attacks. However, the effect of Adr. on cerebral blood flow during vasovagal reflex has not yet been clarified.PurposeThis study investigated the effect of Adr. on cerebral blood flow during vasovagal reflex in an experimental cat model.MethodsTen cats were tracheotomized and restrained in the supine position with its head raised at a 30-degree angle. Upon vagal neurotomy, the nerve fiber on the cardiac side was subjected to electrostimulation for 1 minute. Intravenous Adr. was infused at 0.25 μg/kg for 30 seconds. The regional blood flows in the nucleus vestibularis, nucleus olivaris inferior and nucleus fastigii were measured by the hydrogen clearance method. Changes in heart rate, blood pressure, and regional blood flow were compared among the three groups; Adr. injection alone (Adr. group), electrostimulation alone (electrostimulation group), and Adr. injection+electrostimulation (Adr.+electrostimulation group).ResultsHeart rate and blood pressure increased in the Adr. group (p<0.01), decreased significantly in the electrostimulation group (p<0.01), whereas there were no changes in the Adr. +electrostimulation group. Blood flows increased in the Adr. group (p<0.01), and decreased in electrostimulation and Adr.+electrostimulation groups (p<0.01). However, there was a more significant decrease in the Adr.+electrostimulation group than in the electrostimulation group (nucleus vestibularis: -3.5 vs. -3.9 ml/min/100 g, p<0.01, nucleus olivaris inferior: -9.4 vs. -2.5 ml/min/100 g, p<0.01, and nucleus fastigii: -7.8 vs. -2.8 ml/min/100 g, p<0.01).ConclusionsAlthough Adr. increased cerebral blood flow, Adr. combined with vagal stimulation reduced blood flow more than vagal stimulation alone. This could be explained by accentuated antagonism.
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Masaki et al. (1998) studied this question.
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