Effects of repeated doses of curare on neuromuscular block in the cat

¹ Department of Physiology, Trinity College, Dublin, Ireland

Comparison was made between durations of d-tubocurarine chloride (DTC)-induced blocks (0.6 mg/kg) in the anterior tibialis muscles of two legs in each of 8 cats. The animals were kept in an unheated wooden shed between experiments. Four animals (controls) received no DTC between muscle preparations; three animals received a standard dose of DTC on 12 occasions between muscle preparations; one animal received 25 standard doses of DTC before first muscle preparation. We found: a) an inverse relationship between block duration with first dose and atmospheric temperature (r = –0.82, P < 0.02); b) block durations in second leg of experimental animals' were shorter than in first, and shortest in animal receiving 25 doses (result was significant even allowing for temperature effect: P < 0.04). It was concluded that: a) temperature effect is a consequence of long-term adaptation to environment; and b) repeated doses of DTC induce tolerance.