STUDIES IN FATIGUE XIV. THE EFFECT OF ADRENALIN ON THE DURATION OF THE LATENT, THE CONTRACTION AND THE RELAXATION PERIODS OF SKELETAL MUSCLE AT REST AND UNDERGOING FATIGUE

¹ From the Department of Pharmacology, Washington University School of Medicine, St. Louis

1. Adrenalin chloride causes a marked decrease in the duration of the latent and contraction periods in the early contractions with an increased height of muscular contraction. The relaxation period is lengthened: may be lengthened as much as 257 per cent in the later contractions.

2. The prolongation of the relaxation period in skeletal muscle may be seen from twenty minutes to one and one-half hours after injections of 5 ml. of a 1:100,000 solution to 12 ml. of a 1:10,000 solution of adrenalin.

3. Cats' muscles not exposed to the action of adrenalin can be fatigued to complete exhaustion without prolongation of the muscle curve (confirmation of Lee).

4. The results with adrenalin upon the prefused isolated non-fatigued frog's and cat's skeletal muscles were so variable that no conclusions could be drawn. The same quantity of adrenalin added to the perfusate caused increased height of contraction in some cases, no effect in others and a depression of muscular activity in others. Large doses caused lowered height of contraction in most instances.

5. Adrenalin chloride brings about a true increase in the height of contraction due possibly to increased irritability, to increased available energy or to its action as a catalyst in muscle metabolism. It shortens the durations of the latent and contraction periods.