Expression and functions of the duodenal peptide secretin and its receptor in human lung.

The physiological role of the duodenal peptide secretin is as a potent stimulant of electrolyte and water movement in pancreatic and biliary epithelium, via activation of G protein-coupled secretin receptors (hSCTR). However, the distribution and potential function of hSCTR in human lung has not previously been addressed. Using real-time quantitative reverse transcriptase-polymerase chain reaction profiling, in situ hybridization, and immunohistochemistry, we demonstrated that the hSCTR is abundantly expressed within the distal regions of human lung (tertiary bronchus and parenchyma), with negligible expression detected in more proximal regions (trachea, primary, and secondary bronchus). Expression was observed predominantly on the basolateral membrane of the bronchial epithelial layer, with some expression also observed in bronchial smooth muscle. In primary cultures of human tertiary bronchial epithelial cells, secretin was demonstrated to potently stimulate channel-mediated Cl- efflux in a concentration-dependent manner. Secretin was also shown to cause concentration-dependent relaxation of human tertiary bronchial smooth muscle. In summary, these data demonstrate that secretin receptors are present in human lung, and that activation of these receptors with human secretin potently stimulates concentration-dependent Cl- efflux from bronchial epithelial cells and bronchorelaxation.

EP4 prostanoid receptor-mediated vasodilatation of human middle cerebral arteries.

1. Dilatation of the cerebral vasculature is recognised to be involved in the pathophysiology of migraine. Furthermore, elevated levels of prostaglandin E(2) (PGE(2)) occur in the blood, plasma and saliva of migraineurs during an attack, suggestive of a contributory role. In the present study, we have characterised the prostanoid receptors involved in the relaxation and contraction of human middle cerebral arteries in vitro. 2. In the presence of indomethacin (3 microm) and the TP receptor antagonist GR32191 (1 microM), PGE(2) was found to relax phenylephrine precontracted cerebral arterial rings in a concentration-dependent manner (mean pEC(50) 8.0+/-0.1, n=5). 3. Establishment of a rank order of potency using the EP(4)>EP(2) agonist 11-deoxy PGE(1), and the EP(2)>EP(4) agonist PGE(1)-OH (mean pEC(50) of 7.6+/-0.1 (n=6) and 6.4+/-0.1 (n=4), respectively), suggested the presence of functional EP(4) receptors. Furthermore, the selective EP(2) receptor agonist butaprost at concentrations <1 microM failed to relax the tissues. 4. Blockade of EP(4) receptors with the EP(4) receptor antagonists AH23848 and EP(4)A caused significant rightward displacements in PGE(2) concentration-response curves, exhibiting pA(2) and pK(B) values of 5.7+/-0.1, n=3, and 8.4, n=3, respectively. 5. The IP receptor agonists iloprost and cicaprost relaxed phenylephrine precontracted cerebral arterial rings (mean pEC(50) values 8.3+/-0.1 (n=4) and 8.1+/-0.1 (n=9), respectively). In contrast, the DP and FP receptor agonists PGD(2) and PGF(2 alpha) failed to cause appreciable relaxation or contraction at concentrations of up to 30 microm. In the absence of phenylephrine contraction and GR32191, the TP receptor agonist U46619 caused concentration-dependent contraction of cerebral artery (mean pEC(50) 7.4+/-0.3, n=3). 6. These data demonstrate the presence of prostanoid EP(4) receptors mediating PGE(2) vasodilatation of human middle cerebral artery. IP receptors mediating relaxation and TP receptors mediating contraction were also functionally demonstrated.