Effect of breathing helium on sympathetic nervous and cardiovascular functions

Following the suggestion that the antiarrhythmic action of helium is mediated by changes in sympathetic activity, the effect of He O₂ (80:20) on sympathetic function was investigated. The unanesthetized rat with indwelling cannulae and the pithed rat both responded to norepinephrine (NE), tyramine, and dimethylphenylpiperazinium similarly in He O₂ (31°C) as in air (36°C). Furthermore, He O₂ failed to alter the depressor response to a 45° tail down tilt in either rats or guinea pigs. Likewise, He O₂ did not alter the response of the cat nictitatingl25w10=discussed membrane to preganglionic stimulation. Finally, the effect of He O₂ on the turnover of cardiac NE was examined. Following injection of ³H L NE, the turnover of NE, as measured by the rate of fall of tritium and the endogenous level of NE, was identical in rats exposed to He O₂ (31°C) and to air (26°C). It is concluded that helium does not affect sympathetic nervous or cardiovascular function in the species studied.