THE EFFECT OF ATROPINE UPON MAMMALIAN STRIATED MUSCLE

¹ Neurology Branch, U. S. Army Chemical Warfare Laboratories, Army Chemical Center, Maryland

Its isometric preparations of the tibialis anticus muscle of the cat, dog and monkey, relatively close intraarterial injections of atropine produce an immediate and transient inhibition of the response of voluntary muscle to nerve stimulation. Sensitivity varies widely, 1 to 2 mg/kg producing 50 to 100% block.

Following the recovery of the response to nerve stimulation thse residual amount of atropine in muscle exerts a cumulative action up to 30 min or longer. Inhibition of the reaction to injected ACh is demonstrable during this period of time after the apparent recovery of the response to nerve stimulation.

After injection of potentiating amounts of one of the anticholinesterase agents the manifestation of atropine block is greatly prolonged, namely for a period of 30 to 60 units, in contrast to 1 or 2 min in the normal muscle.

The minimal, effective, intraarterial dosages of atropine to block the responses to nerve stimulation at frequencies of 50/sec,5/sec,and 0.5/sec are respectively 25 mg/kg, 50 mg/kg and 100 mg/kg in normal muscle.

After a potentiating amount of ams anticholinesterase 10 mg/kg of atropine intravenously exerts a slight inhibitory effect.

In isotonic preparations of the normal striated ocular muscles the responses to nerve stimulation and to ACh are inhibited similaly as in skeletal muscle by relatively distant instraarterial injections of atropine.

The results do not indicate any great difference in the susceptibility to atropine inhibitions of the responses to nerve stimulation in typical and in atypical mammalian striated muscle such as obtained with respect to injected ACh.