RELATIVE SUSCEPTIBILITY OF THE NEBULOUS TOAD (BUFO VALLICEPS) AND THE LEOPARD FROG (RANA PIPIENS) TO DIFFERENT SUBSTANCES

¹ From the Lilly Research Laboratories, Eli Lilly and Company, Indianapolis

A comparison of the susceptibility of Rana pipiens and Bufo valliceps to different substances has been made.

The toad is 150 times more tolerant to G-strophanthin, and 86 times more tolerant to scillaren B, than the frog. The tolerance of the toad is localized in its cardiac muscles as shown by the perfusion experiments with scillaren B.

The toad's heart, as compared with the frog's, is resistant to the action of bufagins and bufotoxins, which are pure principles isolated from the toad poisons and have a digitalis-like action. It is, however, equally as sensitive as the frog's heart to epinephrine and bufotenines, which are other active constituents of the toad poisons. That the toad is immune to its own poison is therefore not entirely correct.

The central nervous system, the autonomic nervous system, the muscle nerve endings, and the muscles of the toad do not appear to have a particular resistance to those drugs that are known to act on such systems or tissues. In the case of picrotoxin, strychnine, cocaine and pentobarbital, the toad has a tendency to require a higher dose than the frog for the same effect, but this can be attributed to species difference.

The cardiac tissue is the only one that shows tolerance to the digitaloid glucosides of plant origin and the bufagins and bufotoxins of animal origin.