Further evidence that the guinea pig tracheal contractile serotonergic receptor is a 5-hydroxytryptamine2 receptor: use of 5-methyltryptamine and dipropyl-5-carboxamidotryptamine.
The guinea pig tracheal contractile serotonergic receptor shows pharmacological similarity to both 5-hydroxytryptamine2 (5-HT2) and 5-hydroxytryptamine1C (5-HT1C) receptors. The present in vitro study utilizes 5-methyltryptamine (5-MT), a high-affinity 5-HT1C receptor ligand, and dipropyl-5-carboxamidotryptamine (DP-5-CT), a low-affinity 5-HT1C receptor ligand, as tools to probe the role of 5-HT1C vs. 5-HT2 receptors in tracheal contractility. Both tryptamines contracted trachea with lower potency (-log EC50 < 5) than 5-HT (-log EC50 = 6.98). Maximum contraction to both 5-MT and DP-5-CT was only 50 to 80% of the maximum response to 5-HT, suggesting that these compounds were partial agonists relative to 5-HT. Guinea pig tracheal contraction to 5-HT, 5-MT and DP-5-CT was inhibited by 1-(1-naphthyl)piperazine (1-NP, 30 nM). The apparent antagonist dissociation constants (KB) for 1-NP were similar when 5-HT (-log KB, K = 8.70 +/- 0.17) or 5-MT (- log KB = 8.40 +/- 0.12) were used as agonists. Although 1-NP also blocked tracheal contraction to DP-5-CT, solubility limitations with DP-5-CT did not permit calculation of a KB value for 1-NP. Nevertheless, these data indicate that 5-MT and DP-5-CT interact with the same receptor as 5-HT. As antagonists, both 5-MT and DP-5-CT inhibited tracheal contraction to 5-HT, indicating interaction with the same receptor as 5-HT and confirming partial serotonergic agonist activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Watts
S W
SW
Department of Pharmacology and Toxicology, Indiana University, Indianapolis.
Cohen
M L
ML
D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D011985:Receptors, Serotonin / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D014363:Tryptamines / Q000494:pharmacology*
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D014363:Tryptamines; C027552:5-methyltryptamine; D012701:Serotonin; C055895:N,N-dipropylcarboxamidotryptamine