Modulatory action of galanin on responses due to antidromic activation of peripheral terminals of capsaicin-sensitive sensory nerves

Galanin inhibited. in a concentration-dependent manner (ECso 7.2 nM). the positive inotropic response produced by field stimulation of isolated left atria from reserpine-pretreated guinea-pigs (in the presence of atropine). These responses were shown to involve antidromic activation of capsaicin-sensitive primary afferents. On the other hand. gaJanin did not affect the inotropic response to capsaicin or calcitt'Jnin gene-related peptide. the putative endogenous mediator released from sensory nerves. Galanin-(1-10) was at least 10000 times less potent than the parent peptide. while galanin-{25-29) was ineffective. Likewise. gaJanin inhibited the non-cholinergic contraction produced by field stimulation of the isolated guinea-pig bronchus but not the contraction produced by exogenous neurokinin A. These findings indicate a prejunctional neuromodulatory action of galanin on the excitability of peripheral terminals of capsaicin-sensitive sensory nerves.