Temperature and vagal effects

¹ Donner Laboratory of Medical Physics, Department of Physics and Radiation Laboratory, University of California, Berkeley, California

Vagal effects were observed in isolated vagal heart preparations of Rana pipiens over periods as long as 72 hours. The normal effect was partially blocked by lowering the temperature to about 14°C, and there was a complete block at 10°C and below. On rewarming the preparation the vagal effects recurred; and this process could be repeated cyclically several times. The upper temperature limit of vagal effects seemed to be at 31°C above which the heart stopped. At 32°C however, the stopped heart was still susceptible to stimulation and it could be made to beat for a short time. Tetraethyl pyrophosphate lowered the critical temperature limit by about 3°. The activation energy of vagal effect was calculated in the neighborhood of 46,000 calories, which was similar to value of most enzymic function. It is therefore suggested that the observed phenomenon results primarily from the effect of temperature on choline esterase and acetylase systems.