1 The pharmacology and mRNA expression of endothelin (ET) receptors in human omental arteries were characterized by use of functional contractile assays and the reverse transcriptase-polymerase chain reaction (RT-PCR). 2 In freshly obtained segments of human omental arteries, ET-1 and ET-3 induced concentrationdependent contractions which were normalized to the response produced by 60 mM K+. ET 4 Two-site analysis of the ET-1 induced concentration-response curve from cultured arteries suggests that ETB receptors, at the high potency component, and ETA receptors, at the low potency component, contribute both to the contractile response in relative proportion of 70% and 30%, respectively. Further analysis suggested that the ETA receptor would be capable of evoking at least 75% of the ET-1 contraction in the absence of ETB receptors, although with a lower potency as compared to fresh arteries.5 Electrophoresis of RT-PCR products from the smooth muscle layer of freshly obtained human arteries indicated the presence of mRNA for both ETA and ETB receptors. Arteries cultured for 1 and 5 days demonstrated an increase of mRNA for the ETB receptor as compared to the ETA receptor. The identities of the PCR products were verified by restriction enzyme digestion. 6 In freshly obtained human omental arteries, the contractile effects of endothelins appear to be mediated predominantly by the ETA receptor subtype, with a negligible contribution by ETB receptors. Cultured arterial segments, however, exhibited a substantial ETB receptor mediated contractile response and an increase in ETB receptor mRNA content, consistent with an upregulation of functional ETB receptors. These in vitro data suggest plasticity in the smooth muscle cell expression of contractile ETB receptors.

The ET-1-induced vasoconstriction of human cerebral arteries is primarily mediated by the ETA receptor, whereas the sarafotoxin 6c-induced vasodilatation seems to be mediated via the ETB receptor.

1 Histamine induces relaxation of human cranial arteries. Studies have revealed that the relaxant histamine H 1 -receptor predominates in human cerebral and the H 2 -receptor in temporal arteries, while H 1 -and H 2 -receptors are of equal importance in the middle meningeal artery. The purpose of the present study was to examine the role of the endothelium and nitric oxide in histamine-induced responses and to show the presence of mRNA encoding H 1 -and H 2 -receptors in human cranial arteries. 2 Electrophoresis of polymerase chain reaction (PCR) products from human cerebral, middle meningeal and temporal arteries, demonstrated products corresponding to mRNA encoding both H 1 -and H 2 -receptors in arteries with and without endothelium. The ampli®ed PCR products were sequenced and showed 100% homology with the published sequences of these histamine receptors. 3 A sensitive in vitro system was used to study vasomotor responses to histamine. In precontracted cerebral, middle meningeal and temporal arteries with and without endothelium, histamine caused a concentration-dependent relaxation with I max values between 87% and 81% and pIC 50 values between 8.14 and 7.15. In arteries without endothelium the histamine-induced relaxation was signi®cantly less potent (I max values between 87% and 66% and pIC 50 values between 7.01 and 6.67) than in cranial arteries with an intact endothelium. 4 The addition of histamine to arteries without endothelium and pretreated with the histamine H 2 -antagonist, cimetidine (10 75 M), caused a concentration-dependent contraction of the cranial arteries with E max values between 86% and 29% and pEC 50 values between 7.53 and 6.77. This contraction was blocked by the histamine H 1 -receptor antagonist, mepyramine (10 77 M), and even turned into a relaxation with I max values between 84% and 14% and pIC 50 values between 7.42 and 5.86. 5 The nitric oxide synthase inhibitor N G -nitro-L-arginine methyl ester (L-NAME, 3610 75 M) signi®cantly inhibited the relaxant response to histamine in cerebral and temporal arteries (pIC 50 values between 7.43 and 7.13). The combined treatment with L-NAME (3610 75 M) and cimetidine (10 75 M) caused a further displacement of the concentration-response curve (pIC 50 values between 7.14 and 6.57) and decreased the maximum relaxant responses in all three cranial arteries (I max values between 62% and 39%). 6 In conclusion, this is the ®rst study which show mRNA encoding histamine H 1 -and H 2 -receptors in human cranial arteries. The results indicate that histamine-induced relaxation of human cranial arteries is partially mediated via an endothelial H 1 -receptor coupled to the production of nitric oxide and partially via a H 2 -receptor associated with the smooth muscle cells. In addition, there is evidence for a contractile H 1 -receptor in the smooth muscle cells in these arteries.

No abstract

The aim of our study was to determine the neuropeptide Y (NPY) receptor subtype responsible for the NPY-induced contraction of human subcutaneous (s.c.) resistance arteries. To elucidate this, we used (a) in vitro studies of NPY agonists: NPY, peptide YY (PYY), and Pro34NPY induced equally strong and equipotent concentration-dependent contractions of human s.c. resistance arteries, whereas NPY13-36 and NPY18-36 had no contractile effects; (b) in vitro studies using the NPY Y1-receptor antagonist, BIBP3226, which in nanomolar concentrations inhibited the contractile effect of NPY, causing a rightward shift of the concentration-response curve. pEC50 for NPY alone, 8.41 +/- 0.21; NPY + BIBP3226, 10 nM, 7.79 +/- 0.21; NPY + BIBP3226, 100 nM, 7.18 +/- 0.18; NPY + BIBP3226, 1 microM, 6.32 +/- 0.05 (n = 5-8). Schild-plot analysis indicated competitive antagonism: pA2 = 8.53 +/- 0.22 and slope = 0.99 +/- 0.14; (c) with reverse transcriptase-polymerase chain reaction (RT-PCR), we detected messenger RNA (mRNA) encoding the human NPY Y1 receptor and a splice variant of the receptor in human s.c. resistance arteries. On the basis of the agonists' potency order, the antagonistic effect of BIBP3226 on the NPY-induced contraction, and the presence of mRNA encoding the NPY Y1 receptor, we conclude that the NPY-induced contraction of human s.c. resistance arteries is mediated by NPY Y1 receptors.