Tris buffer, CO₂, and sympatho-adrenal system in reactions to O₂ at high pressure

¹ Department of Physiology, University of Michigan, Ann Arbor, Michigan

The demonstration of the efficacy of tris(hydroxymethyl)aminomethane ("tris") in buffering tissue Pco₂ and acidity suggested that it might provide protection against the toxic action of oxygen at high pressures (OHP). Experiments were therefore carried out on 72 pairs of albino rats. The test animal of each pair was administered tris intraperitoneally and subcutaneously and its control of equal body weight and age was given an equal volume of physiological NaCl solution in a similar manner. The usual dose was 1.5 g/kg body weight, as a 10% solution in physiological NaCl. Each pair was exposed separately. It was found that tris provided a pronounced degree of protection against the toxic action of OHP. It postponed the onset of the O₂ seizures and decreased their incidence and severity. Lung damage was either absent or much less severe in the test animals than in the controls. The lung weight was less and the mortality rate much lower in the test than in the control animals. Statistically, the results, as measured by each of the criteria used, were highly significant (P < 0.01). The results are important not only because they demonstrate that tris provides a pronounced measure of protection against the toxic action of OHP, but also because they redirect attention to increased tissue Pco₂ and tissue [H⁺] concentration as possible contributors to the precipitation of the toxic reaction to OHP.