Systemic effects of epinephrine in the frog.

Abstract

AbstractThe intact frog (R. pipiens) is both very sensitive to i.v. injection of l‐epinephrine (E) in small amounts (a few micrograms), and very tolerant to large doses (several milligrams) of the hormone. A small dose increased the P.D. and the short circuit current (Is) in skin, and strongly increased the strength of auricular contraction of the heart in vivo; ventricular contractions decreased, and heart rate remained normal. Large doses of E depressed P.D. and Is after, occasionally, elevating both for a brief period following treatment. The mucous glands of the skin emptied their content shortly after E, then began to fill again with secretory materials in spite of uninterrupted E infusions. Ventricular and auricular contractions were remarkably little altered and there were no significant changes in heart rate. Changes were seen, however, in the ECG, e.g.: inversion of the P and T waves. No alteration in the QRS complex or in the rhythm was ever noted. Serum glucose remained within normal limits. A transient calorigenic effect, lasting for 10–20 minutes occurred, in which the O2 consumption rose from a normal of 6 to 7 ml/100 g/hr to several times this value. Unanesthetized frogs tolerated without great harm 10 mg of E given s.c. within one hour. Signs of prostration and a moderate increase in respiration were noted for some time following treatment. Great tolerance of frogs to hormones which do play a physiological role is also known for thyroxine and insulin, but is especially notable for epinephrine which is least tolerated by warmblooded animals treated with large doses of E. The reasons for these species differences are unknown.