MK exerts a potent antagonist activity against the particularly potent constricting effects of CysLTs in isolated human small bronchi, which only expressed the CysLT1 receptor subtype. The metabolites of MK are also potent in vitro antagonists, but may not participate in the therapeutic activity of MK due to their low plasma concentrations in patients treated with the recommended dose of MK.

The aims of this study were to determine the cysteinyl leukotriene (CysLT) receptors expressed in the human saphenous vein, to examine contractile response to LTC4 and LTD4, to evaluate antagonist activity of montelukast, a specific CysLT1 receptor antagonist used in asthma, and to characterize the CysLT receptors involved in the contractile response. The analysis by reverse-transcriptase polymerase chain reaction indicated that CysLT1 and CysLT2 receptors are expressed by saphenous veins. In varicose vein rings, the potencies (pD2) of LTC4 and LTD4 were similar: 7.4 +/- 0.2 and 7.4 +/- 0.1, respectively. Pretreatment with acivicin, a gamma-glutamyl transpeptidase (gamma-GT) inhibitor, to prevent potential metabolism of LTC4 to LTD4, did not alter the response to LTC4. In nondistended vein rings from patients undergoing arterial bypass, the LTC4 pD2 was 7.8 +/- 0.1, and pretreatment with S-hexyl-GSH, a potent gamma-GT inhibitor, caused a fourfold rightward shift of the LTC4 concentration-response curve. In varicose and nondistended saphenous vein rings, montelukast (10(-8) and 10(-7) M) exerted a potent activity against LTD4 and LTC4, in the presence or absence of gamma-GT inhibitors. In varicose vein rings, the two active metabolites of montelukast also exerted antagonist activities with potencies similar to montelukast. BAY u9773 (CysLT2 agonist/dual CysLT1/CysLT2 antagonist) did not cause contraction and inhibited the LTC4- and LTD4-induced contractions. In conclusion, human saphenous veins express CysLT1 and CysLT2 receptors, but only CysLT1 receptors are implicated in the contraction.

The effects of neurokinins and neurokinin receptor selective agonists have been investigated on human intralobar pulmonary vessels. Substance P (SP) and [Sar(9) Met(O(2)) ]SP(11), a selective NK(1) receptor agonist, induced concentration-dependent relaxation of pulmonary vessels precontracted with phenylephrine. The mean negative log (M) EC (50) values for SP and [Sar (9) Met(O2))]SP(11) were 8.6 and 8.9, respectively, on arterial preparations and 8.9 and 8.6, respectively, on venous preparations. Relaxations to [Sar(9) Met(O(2) ) ]SP were abolished by the NK receptor antagonist SR140333. The relaxations to a second application of [Sar(9) Met(O (2)) ]SP were markedly reduced, suggesting a rapid desensitization of the NK(1) receptor. Such desensitization was not observed with acetylcholine. The selective NK receptor agonist, [Nle(10)]NKA, and the selective NK (3) receptor agonist, [MePhe(7)]NKB, caused neither contractions nor relaxations of pulmonary vessels. The NK(1) receptor-mediated relaxations were abolished by removing the endothelium or by a combination of -nitro-L-arginine and indomethacin, whereas each compound exerted a partial inhibitory effect. Similar results were observed with acetylcholine. Positive immunostaining for NK(1) receptors was only found in the endothelium. Reverse transcription-polymerase chain reaction detected messenger RNA for NK(1) receptors without any detection of messenger RNA for NK(2) or NK(3) receptors. In conclusion, human pulmonary arteries and veins express endothelial NK(1) receptors that mediate relaxation through a combination of cyclooxygenase and nitric oxide activities and are subjected to rapid tachyphylaxis.

Although prostanoids are known to be involved in regulation of the spontaneous beating rate of cultured neonatal rat cardiomyocytes, the various subtypes of prostanoid receptors have not been investigated in detail. In our experiments, prostaglandin (PG)F2α and prostanoid FP receptor agonists (fluprostenol, latanoprost and cloprostenol) produced a decrease in the beating rate. Two prostanoid IP receptor agonists (iloprost and beraprost) induced first a marked drop in the beating rate and then definitive abrogation of beating. In contrast, the prostanoid DP receptor agonists (PGD2 and BW245C) and TP receptor agonists (U-46619) produced increases in the beating rate. Sulprostone (a prostanoid EP1 and EP3 receptor agonist) induced marked increases in the beating rate, which were suppressed by SC-19220 (a selective prostanoid EP1 antagonist). Butaprost (a selective prostanoid EP2 receptor agonist), misoprostol (a prostanoid EP2 and EP3 receptor agonist), 11-deoxy-PGE1 (a prostanoid EP2, EP3 and EP4 receptor agonist) did not alter the beating rate. Our results strongly suggest that prostanoid EP1 receptors are involved in positive regulation of the beating rate. Prostanoid EP1 receptor expression was confirmed by western blotting with a selective antibody. Hence, neonatal rat cardiomyocytes express both prostanoid IP and FP receptors (which negatively regulate the spontaneous beating rate) and prostanoid TP, DP1 and EP1 receptors (which positively regulate the spontaneous beating rate).