Characterization of the contractile serotonergic receptor in guinea pig trachea with agonists and antagonists

5-Hydroxytryptamine (5-HT)2 receptors can be partially characterized by their sensitivity to ketanserin blockade and increase in phosphoinositide turnover upon stimulation. Previously, the contraction of guinea pig trachea to 5-HT was shown to be antagonized by the 5-HT2 receptor antagonists ketanserin and LY53857. However, 5-HT did not dramatically increase phosphoinositide turnover in guinea pig trachea, suggesting that the contractile receptor may be different from the classically defined 5-HT2 receptor. The present in vitro studies better characterize this receptor, using diverse serotonergic agonists and antagonists to profile in more detail the contractile serotonergic receptor in guinea pig trachea. With regard to agonists, the 5-HT2 receptor agonists DOI and alpha-methyl-5-HT contracted guinea pig trachea with greater potency than quipazine, 5-methoxytryptamine, 5-carboxamidotryptamine, 8-hydroxy-2-(di-N-propylamino)tetralin and 2-methyl-5-HT. Sumatriptan and 1-(3-chlorophenyl)-piperazine (10 nM-100 microM) were inactive as agonists. A strong correlation between agonist potency (EC50) and reported 5-HT receptor binding affinities was found for both the 5-HT1C (r = 0.890) and 5-HT2 (r = 0.831) receptor. Ketanserin, spiperone, ritanserin, LY53857, 1-napthylpiperazine, 1-(3-chlorophenyl)-piperazine, rauwolscine, ICS 205-930, cyanopindolol and sumatriptan all blocked 5-HT-induced contractions in guinea pig trachea. As occurred with agonist potencies, strong correlations were found between reported 5-HT1C (r = 0.814) and 5-HT2 (r = 0.912) receptor binding affinities in brain membranes and apparent dissociation constants (KB) for the 10 antagonists of 5-HT induced contraction in guinea pig trachea.(ABSTRACT TRUNCATED AT 250 WORDS)