Influence of pertussis toxin on the calcitonin-opioid interaction in isolated tissues.

1. In order to clarify one of the mechanisms involved in the analgesic effect of calcitonin, we have tested the in vitro modifications induced by calcitonin on the effect of opioids. 2. The inhibition of the contractions induced by opioids or clonidine, in guinea-pig ileum or in mouse vas deferens, were significantly reduced in tissues incubated with pertussis toxin (PTX). When tissues were incubated with PTX and calcitonin, the inhibitory effect was restored. 3. These results suggest that calcitonin is able to potentiate a non-PTX-sensitive mechanism of transduction and support the possibility of involvement of similar G-proteins in the effects of opioid and alpha 2-adrenoceptor agonists.