Relationship between 5-HT 2A receptor mRNA density and contractility in trachea and aorta from guinea pig and rat

Abstract

The present studies document marked differences in contractile responsiveness to serotonin in trachea and aorta between guinea pig and rat. For example, the guinea pig trachea and rat aorta markedly contract in response to serotonin via activation of 5-HT 2A receptors. In contrast, the rat and guinea pig aorta only modestly contract to serotonin. The availability of 5-HT 2A receptor selective cDNA clones from brain of both guinea pig and rat permitted molecular probes to be designed and PCR amplification studies initiated to identify and quantify 5-HT 2A receptor specific mRNA in these tissues. For trachea, 3-fold higher concentrations of 5-HT 2A receptor specific mRNA were found in guinea pig relative to rat trachea. These data are consistent with the more profound contractile response to serotonin in guinea pig versus rat trachea and suggest that differences in tracheal contractility to serotonin correlate with the density of 5-HT 2A receptor mRNA. In contrast, although rat aorta contracted more dramatically to serotonin than guinea pig aorta, rat aorta possessed a similar concentration of 5-HT 2A receptor specific mRNA as compared to guinea pig aorta. Thus, for the aorta, differences in the concentration of 5-HT 2A receptor mRNA are not sufficient to explain the observed differences in contractility between tissues from guinea pig and rat. These studies documenting 5-HT 2A receptor mRNA in rat trachea and guinea pig aorta, two tissues that do not markedly contract in response to serotonin indicate that 5-HT 2A receptor mRNA although present, has not resulted in a receptor capable of mediating a contractile response in these tissues.