Vagal effects on heart rate in rabbit, A preliminary report
Cevese, A.; Brazzoli, C.; Poltronieri, R.; Zaffagni, C.
Bollettino della Societa Italiana di Biologia Sperimentale 57(13): 1389-1394
1981
ISSN/ISBN: 0037-8771 PMID: 7284106 Document Number: 173928
The concept of an asymmetrical organ (the heart) regulated by a symmetrical efferent autonomic innervation was examined. Special attention was paid to the effects of stimulation of the right (R), the left (L), and both (RL) vagi nerves on heart rate (R-R intervals) in rabbits, using a wide range of stimulation frequencies (ST-ST intervals), at supramaximal voltage. No difference in the effect of R and L was found. The response to RL was greater than that to R or L, but 10-20% smaller than the summated responses to single nerve stimulations, revealing a partial occlusion. A common pattern of the R-R variations as a function of St-St, characterized by a discontinuous curve, with a very low slope for frequencies of stimulation lower than the basal heart period and a steep exponential relation for higher frequencies was found. Such a pattern apparently is due to temporal summation of the effect, which is not possible with St-St intervals longer than R-R intervals, but becomes fully developed for shorter St-St intervals.