A mechanism by which helium increases metabolism in small mammals

Abstract

The oxygen consumption of male Long-Evans rats was determined at three different ambient temperatures in air and in an equivalent helium-oxygen mixture. It was found that when the ambient temperature is near the skin temperature of the rat, the effect of helium is insignificant. If the ambient temperature is lowered, helium induces an increased metabolism over air at the same temperature. Since helium has a thermal conductivity about six times greater than nitrogen, it is concluded that the accelerated metabolism is in response to the greater heat loss in the presence of helium and the magnitude of this response is proportional to the thermal gradient between the animal and the environment.

Biochemical and metabolic effects of a six-month exposure of small animals to a helium-oxygen atmosphere

“…The four sets of mice also had higher oxygen consumptions in helium -oxygen than in air. These results are in agreement with the findings of others (Leon and Cook, 1960;Rhoades et aL, 1966), and on mice raised in helium-oxygen and nitrogenoxygen in this Laboratory (Schreiner, Bruemmer, and Doebbler, 1965) . This effect has been attributed, as previously mentioned, to the helium thermoconductivity-heat maintenance problem of mammals.…”

“…Small mammals show a consistent increase in metabolism as evidenced by an increase in oxygen consumption, carbon dioxide production, and food consumptlOn (see Roth, 1965, for a review) . This phenomenon seems to be due to the thermal properties of helium, since the increase is typical of the thyroxine-induced overdose that follows cold exposure (Leon and Cook, 1960). Further i nd irect evidence hat heat loss is causing the helium effect is shown in a previous report from t his laborat ory (Hamilton5l!, al., 1966 b) which reveals a convincing correIa lOn between oxygen consumption and convective heat loss m small animals exposed to a t mospheres having different thermal properties .…”

“…It has been assumed the increased metabolism is caused by the high thermal conductivity of helium and that, therefore, mammals need to produce sufficient additional heat to maintain body temperature in the face of increased convective heat loss (Leon and Cook, 1960). This effect may mask other factors which could also change the rate of oxygen consumption .…”

“…This was confirmed in subsequent studies conducted at our laboratory (Schreiner, Bruemmer, and Doebbler, 1965). The degree of metabolic acceleration , in the presence of helium, also diminished when the standard metabolic rate of the animals was increased by a variety of means (Leon and Cook, 1960) . Hamilton~ al.…”

“…Leon and Cook (1960) demonstrated that the accelerated metabolism of rats exposed to a helium-oxygen environment was most likel y due to the greater heat loss in the presence of helium since the magnitude of this response decreases as t h e temperature differential between the animal and its gaseous environment decreases. This was confirmed in subsequent studies conducted at our laboratory (Schreiner, Bruemmer, and Doebbler, 1965).…”