Selective desensitization of 5-hydroxytryptamine 2A receptor mediated contraction in guinea pig trachea.
5-Hydroxytryptamine (serotonin, 5-HT) contracts the guinea pig trachea through stimulation of 5-HT2A receptors, an effect previously reported to rapidly desensitize. The present studies were designed to examine further the putative desensitization to serotonin. In vitro studies investigating functional desensitization of the guinea pig tracheal 5-HT2A receptor documented that 5-HT (3 x 10(-7) M) significantly (50%) but incompletely reduced subsequent tracheal maximal contraction to 5-HT. In contrast, an equieffective concentration of carbamylcholine (3 x 10(-8) M) did not reduce guinea pig tracheal contraction to 5-HT. Furthermore, 5-HT (3 x 10(-7) M) did not diminish tracheal contraction to carbamylcholine. These data indicate that 5-HT can selectively desensitize guinea pig tracheal contraction to 5-HT. In addition, 5-HT-induced contraction but not carbamylcholine-induced contraction in guinea pig trachea declined over time, an effect that was more pronounced at high concentrations of 5-HT (1 x 10(-6) and 1 x 10(-5) M). Inhibitors of mechanisms that oppose contractility to 5-HT (5-HT-induced relaxation, uptake of 5-HT, or metabolism of 5-HT) did not reverse the decline in contraction to 5-HT (1 x 10(-5) M). The decline in 5-HT-induced contraction was most rapid in the guinea pig trachea and less so in the rat jugular vein and rat aorta, two preparations in which 5-HT induced contraction also occurred via activation of 5-HT2A receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Watts
S W
SW
Department of Pharmacology and Toxicology, Indiana University, Indianapolis 46227.
Schenck
K W
KW
Cohen
M L
ML
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; 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*; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology*; D012680:Sensitivity and Specificity; D012701:Serotonin / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure*
D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D012701:Serotonin; D002217:Carbachol