Characterisation of functional endothelin receptors in the canine isolated perfused spleen

Characterization of endothelin receptors in isolated, perfused human spleen

At present, there is no information on endothelin-1 (ET-1)-mediated vascular effects in the human spleen. The objectives of this study were to investigate the in vitro vascular responses to ET-1 using pharmacologic probes (selective ET receptor agonists/antagonists) and to characterize the ET receptor population in the human spleen. Spleens (n = 6) were removed from patients for treatment of underlying disease. The organs were perfused with warmed (37 degrees C), oxygenated (95% O2/5% CO2) Krebs solution at constant flow, with continuous recording of splenic arterial perfusion pressure (SAPP). The increases in SAPP caused by injection of ET-1 (ETA/ETB agonist) were markedly reduced in the presence of the selective ETA antagonist FR-139317, whereas those induced by IRL-1620 (an ETB agonist) and norepinephrine (NE) were unchanged. The increases in SAPP induced by intra-arterial bolus injections of NE and ET-1 were significantly (p < 0.05) potentiated by indomethacin [INDO; a cyclo-oxygenase (COX) inhibitor] alone and the responses to both peptides (ET-1 and IRL-1620) were significantly (p < 0.05) potentiated by INDO and L-NAME [a nitric oxide (NO) synthase inhibitor] together. We conclude that ET-1 contributes to the regulation of vascular tone in human spleen through activation of both ETA and ETB receptors and that these responses are modulated by concomitant release of prostaglandins and NO.

Involvement of nitric oxide in the smooth muscle tone of the isolated canine spleen and the responses to acetylcholine and substance P

1. The canine isolated spleen was perfused at constant flow with warmed (37 degrees C) Krebs solution while the splenic arterial perfusion pressure (SAPP) and spleen weight were recorded continuously. An augmented smooth muscle tone was maintained by a continuous intra-arterial infusion of noradrenaline (0.01-0.1 mumol min-1) throughout the experiment. 2. Intra-arterial infusion of indomethacin (5.6 microM) significantly elevated (P < 0.05) the augmented vascular tone and the subsequent infusion of L-NAME (10 microM) further raised this vascular tone significantly (P < 0.01). 3. The splenic vasoconstrictor response to L-NAME was significantly (P < 0.05) reduced by the subsequent infusion of L-arginine (300 microM) but not of D-arginine (300 microM). 4. Neither L-NAME nor D-NAME had any effect on the basal vascular tone or the spleen weight in conditions of either basal or augmented tone. 5. Bolus injection of acetylcholine, substance P, sodium nitroprusside and isoprenaline caused short-lasting reductions in the SAPP. 6. The splenic vasodilator responses to ACh and SP, but not those to SNP and ISO, were significantly (P < 0.05) reduced by the infusion of L-NAME (10 microM), methylene blue (30 microM) but not of D-NAME (10 microM). 7. The reductions in the vasodilator responses to ACh and SP caused by L-NAME were partially reversed by L-arginine (300 microM), but not by D-arginine (300 microM). 8. The results demonstrate the contribution of nitric oxide (NO) release to the maintenance of the augmented splenic vascular tone and also the contribution of NO to the splenic vasodilator responses to ACh and SP.