Effects of diethyl-stilboestrol on single fibres of frog skeletal muscle.

The effects of diethyl-stilboestrol (DES), one of the most potent estrogens, were studied on single muscle fibres of the frog. In relatively low concentrations (5 muM), DES greatly potentiates the twitch response of the fibre without significantly affecting the amplitude of the tetanus response. The twitch potentiation is accompanied by an increase in time to peak tension and marked prolongation of the relaxation phase. In tetanic response the half decay time after the last stimulus is also prolonged by DES. DES causes no changes in the resting or action potential of the muscle fibre. The S-shaped curve relating peak contracture tension and caffeine concentration is shifted towards lower caffeine concentrations by DES. Dantrolene greatly suppresses the DES potentiated twitch. It is concluded that DES potentiates the twitch response and prolongs the relaxation time by inhibition of the calcium re-uptake by the sarcoplasmic reticulum.