Calcitonin reverts pertussis toxin blockade of the opioid analgesia in mice

The aim of this paper is to study the influence of salmon calcitonin (SCT) on opioid analgesia when opioid transduction pathways are functionally unco upled from G(i/o) proteins by treatment with pertussis toxin (PTX). The ant inociceptive effect of morphine and three selective opioid agonists, [D-Ala (2),N-Me-Phe(2),Gly(5)-ol]enkephalin (DAMGO) (OP3-mu receptor agonist), [D- Pen(2,5)]-enkephalin (OP1-delta receptor agonist) and trans-(+/-)-3,4-dichl oro-N-methyl-N-[2-1(-pyrrolidinyl)-cyclohexyl]-benzene-acetamide methane su lfonate (U-50, 488H) (OP1-kappa receptor agonist) was evaluated, using the tail flick test, in mice treated with PTX or with PTX and SCT. PTX blocked the antinociceptive effect of the opioids, being the antinociception simila r in control animals and in mice treated with PTX and SCT. Thus, SCT preven ts the effect of the blockade of G(i/o)-proteins. From this it could be sug gested that calcitonin activates alternative antinociceptive mechanisms tha t are not dependent on G(i/o)-proteins. (C) 1999 Elsevier Science Ireland L td. All rights reserved.