Studies on the sensitivity of the iris of amphibians (Hyla arborea and bufo viridis) to epinephrine and norepinephrine

Abstract

• 1. Epinephrine and norepinephrine administered to Bufo viridis and Hyla arborea by injection, by dripping into the conjunctival sac and per os as well as in vitro, on isolated eyes, were found to cause mydriasis.

• 2. Hyla arborea were almost equally sensitivie to both catecholamines and showed, in the majority of cases, a higher sensitivity when compared to Bufo viridis, which however, exhibited a better response to injected epinephrine than to norepinephrine.

• 3. By using other routes of administration both substances were in general less effective, probably on account of their vasoconstrictive activity on the conjunctival and intestinal capillaries, which decreases penetration.

• 4. The results showed that in amphibians, as well as in mammals, no correlation exists between the physiological proportion of both catecholamines in nerves and their pharmacological mydriatic activity, and a possibility that neurohormones of adrenal medullar source might participate in the physiological mydriatic mechanism was suggested.