Mechanical effects of some prostanoids on isolated human oesophageal submucosal veins

Functional oesophago-gastric junction imaging

Despite its role in disease there is still no definitive method to assess oesophago-gastric junction competence (OGJ). Traditionally the OGJ has been assessed using manometry with lower oesophageal sphincter pressure as the indicator. More recently this has been shown not to be a very reliable marker of sphincter function and competence against reflux. Disorders such as gastro-oesophageal reflux disease and to a lesser extend achalasia still effects a significant number of patients. This review looks at using a new technique known as impedance planimetry to profile the geometry and pressure in the OGJ during distension of a bag. The data gathered can be reconstructed into a dynamic representation of OGJ action. This has been shown to provide a useful representation of the OGJ and to show changes to the competence of the OGJ in terms of compliance and distensibility as a result of endoluminal therapy.

Endothelium-dependent relaxation by substance P in human isolated omental arteries and veins: relative contribution of prostanoids, nitric oxide and hyperpolarization

1. The objective of the present study was to investigate human omental arteries and veins with respect to: (i) the contractile effect of the thromboxane A2 analogue U46619, (ii) endothelium-dependency and mediators of the relaxing effect of substance P (SP) and acetylcholine (ACh). 2. Changes in isometric tension in response to administration of U46619, SP and ACh were measured in human isolated omental arteries and veins with and without endothelium. To investigate the mechanism of action of SP, the SP-induced relaxation was measured in the presence of indomethacin (cyclo-oxygenase inhibitor), NG-monomethyl-L-arginine (L-NMMA, nitric oxide-synthase inhibitor), KCl (inhibitor of endothelium-dependent hyperpolarization), tetraethylammonium (TEA; non-selective inhibitor of K(+)-channels, with some preference for the high conductance Ca(2+)-activated K(+)-channel, BKCa), glibenclamide (inhibitor of the ATP-sensitive K(+)-channel) and/or clotrimazole (inhibitor of the cytochrome P450-system and the intermediate conductance Ca(2+)-activated K(+)-channel, IKCa). 3. U46619 contracted both the artery and the vein segments. Endothelium removal did not alter the contraction. 4. ACh caused neither contraction nor relaxation in artery and vein segments precontracted with U46619. 5. In both artery and vein segments precontracted with U46619, SP produced endothelium-dependent relaxation. The relaxation was unaffected by indomethacin, but was incompletely reduced by L-NMMA and KCl respectively. The L-NMMA-resistent relaxation was abolished in the presence of KCl. 6. TEA inhibited the SP-induced relaxation in artery and vein segments both in the presence and absence of L-NMMA and indomethacin, while glibenclamide and clotrimazole had no effect. 7. In conclusion, the SP-induced relaxation in human omental arteries and veins seems to be mediated via NO and endothelium-dependent hyperpolarization. KATP and IKCa are probably not involved in the hyperpolarization, but activation of BKCa may contribute to the hyperpolarization. Prostanoid synthesis and the cytochrome P450-system are probably not involved in the SP-induced relaxation in this area.

Effects of prostaglandins E1 and E2 on cultured smooth muscle cells and strips of rat aorta

Using patch-clamp and Indo-1AM techniques, we studied the effects of prostaglandins (PG) E1 and E2 on transmembrane ionic currents and cytosolic calcium concentration ([Ca2+]i) in cultured rat aortic smooth muscle cells (SMC) and on isotonic contraction-relaxation of strips of the rat thoracic aorta. In voltage-clamped at -70 mV single SMC PGE1 and PGE2 in concentration 100 nM evoked inward and outward currents. The inward current was unaffected by the Cl channel blocker DIDS (0.1 mM). The outward current was blocked by internal Cs+ and external Ba2+ and was likely due to increased Ca2+ activated K+ conductance. Application of PGE1 and PGE2 in the bath solution evoked relaxation of aortic strips in a concentration-dependent manner. In both cases indomethacin was ineffective. The rise in [Ca2]i evoked by PGEs was observed in single cells loaded with Indo-1AM. Whole-cell voltage-activated T- and L-type Ca2+ currents were reduced by both PGE1 and PGE2. The results obtained in this work indicate that in cultured rat aortic SMC PGE1 and PGE2 increase [Ca2+]i with subsequent activation of Ca(2+)-dependent K+ currents, block voltage-activated Ca2+ currents, and at the same time induce relaxation of aortic strips.