Following a recent suggestion that the anti arrhythmic effect of breathing helium oxygen (He O2) is mediated by changes in sympathetic activity, the effect of He O2 (80:20) on autonomic function was investigated. The unanesthetized, unrestrained rat with indwelling cannulae, responded to pressor doses of norepinephrine (NE), tyramine and dimethylphenylpiperazinium in a similar fashion whether in an environment of He O2 at 31°C or nitrogen oxygen (N2 O2; 80:20) at 26°C ambient temperature. Again using the same rat as its own control, it was found that He O2 did not alter the fall in arterial pressure which followed a 45° taildown tilt in animals anesthetized with pentobarbital. Likewise, He O2 had no effect on the response of the nictitating membrane to preganglionic stimulation in the cat anesthetized with pentobarbital. Finally the effect of He O2 was examined on the cardiac turnover of 3H L NE. Rats were injected with 3H L NE (33.3 μCi/kg; tail vein) and 20 rats were exposed to He O2 at 31δC while another group of 20 rats was exposed to N2 O2 at 26°C. Rats were killed at 2, 6, 12 and 23 hr after injection and the levels of both endogenous and labelled NE determined; the absolute level of NE and the rate of decline of tritiated amine were similar in both groups. It was concluded that He O2 does not affect autonomic nervous function in the species studied.
|Number of pages||1|
|Issue number||3 I|
|Publication status||Published - 1974|