[Effect of the vagus nerve on isolated rabbit atria in ganglionic blockade due to hexamethonium]

By quantitative stimulation of the vagus nerves of isolated rabbit atria frequency-response relations were obtained for both the electrotropic effect (reduction of the area of the monophasic action potential) and the inotropic response. An addition of hexamethonium in a final concentration of 10(-5) g/ml resulted in a diminution of vagal effectivity in the range of lower and medium frequencies of stimulation, and was connected with a shift of the frequency-response characteristic to the right. At higher frequencies vagal effectivity was increased. In contrast to the inhibitory effect of hexamethonium the facilitating action is irreversible. By raising the concentration up to 4-10(-5) g/ml the vagal effects were reduced to a large extent, and the frequency dependence of the response was abolished at medium frequencies. In the range of 20 sec(-1) to 100 sec(-1) this dependence was re-established and may be considered as a part of a normal frequency-response relation extremely shifted to the right. The time courses of both types of effect are characterized by a steep rise and a decay of the response during the stimulation period. A mathematical handling of the frequency-response characteristics provides quantitative evidence for the extent of the hexamethonium blockade of vagal ganglion cells in the atria; furthermore it leads to the conception of these cells to act as a distributing system for a homogeneous innervation by a widespread divergency of postganglionic fibres.