Effect of Hypothermia on the Tolerance of Dogs to Digitalis

H modifies to a considerable degree the effects of various drugs. Among those investigated in the past have been central nervous system stimulants and depressants, hormones, epinephrine, acetylcholine, insulin, thyroid, ethyl alcohol, Dicumarol, oxygen, carbon dioxide, procaine, and cocaine. However, the effect of hypothermia on the action of digitalis has not been extensively investigated. Most of the studies performed have been obtained from cold-blooded animals and in isolated hearts. Experiments on the frog," using various digitalis glycosides, revealed a progressive increase in the mean lethal dose (MLD) of the drug as the temperature was lowered. Studies on isolated rabbit and chick hearts' " revealed similar findings. It is also of interest to note that with an increase above normal in the body temperature, a decrease in the toxic dose of digitalis was observed.' Only a few reports are available on the tolerance of the warm-blooded animal to digitalis under hypothermic conditions. Most of these are limited to a relatively few animals or involve a comparison of certain degrees of toxicity. For example, in one study of four cats during hypothermia, the dose of digitalis required to produce cardiac arrest was twice that observed in four normothermic animals. In another report, the toxicity of ouabain, as determined by the production of extrasystoles, was compared to that of the hypothermic animal (temperature 26 ± 1 C.);