Drugs given intra-renal arterially (i

Drugs given intra-renal arterially (i.r.a.) were injected in a volume of 30?l into the femoral arterial line a self-sealing rubber insert, and then flushed into the kidney by the saline infusion. selective ETA receptor antagonist “type”:”entrez-nucleotide”,”attrs”:”text”:”FR139317″,”term_id”:”258103156″,”term_text”:”FR139317″FR139317 at 0.3 and 1.0?mg?kg?1 had no effect on basal levels of blood pressure, renal vascular resistance or renal blood flow. The lower dose of “type”:”entrez-nucleotide”,”attrs”:”text”:”FR139317″,”term_id”:”258103156″,”term_text”:”FR139317″FR139317 had no effect on the ET-1 dose-response curve for renal blood flow while at 1.0?mg?kg?1, “type”:”entrez-nucleotide”,”attrs”:”text”:”FR139317″,”term_id”:”258103156″,”term_text”:”FR139317″FR139317 reduced the EC50 to 36332?ng (ETB rather than ETA receptors. Moreover, both ET-1 and ET-3 dependent vasoconstrictions are slightly attenuated by concomitant NO production. By contrast, sarafotoxin 6c appears much more potent at the renal resistance vasculature and is much more powerfully modulated by NO. and show a high level of peptide sequence homology with the endothelins. Two major endothelin receptor subtypes have been identified pharmacologically, their genes cloned (Arai using rat arcuate arteries confirmed this view (Wu studies (Pollock & Opgenorth, 1993) showed that systemic i.v. Apelin agonist 1 infusion of ET-1 significantly increased mean arterial pressure (MAP) and reduced renal plasma flow (RPF) but that administration of the ETA receptor antagonist BQ123 blocked the increase in MAP, but Fgfr1 did not prevent the significant decrease in RPF. This was in contrast to other vessels such as the carotid and iliac arteries where the ETB agonist (Ala 1, 3, 11, 15) ET-1 elicited vasodilatation as opposed to vasoconstriction. The distribution of endothelin Apelin agonist 1 receptor subtypes alters along the renal vascular tree, from predominantly ETA receptors in the rat renal artery (Clark & Pierre, 1995), to mainly ETB receptors on post-glomerular vessels (Endlich NO production. One of the confounding problems at the present time is that many studies have employed systemic infusion of endothelin to study their action on renal haemodynamics. The difficulty is that under these circumstances, the renal vascular responses will be an amalgam of an indirect component due to the raised systemic blood pressure (primarily mediated by ETA receptors) and a direct one involving both ETA and ETB or only the ETB receptor subtype. In an attempt to address these issues, studies were undertaken in anaesthetized rats prepared for renal haemodynamic measurements, in which localized intra-renal arterial infusions of ET-1, ET-3 and sarafotoxin 6c were given at levels having no systemic effects. Cumulative dose responses were drawn up alone and in the presence of a local infusion of an ETA receptor antagonist. The contribution of nitric oxide in these responses were investigated by preventing its generation with concomitant L-NAME administration. Methods Surgical preparations: All surgical procedures were performed under the provisions of the United Kingdom Government project licence PPL40/1367 and personal investigator licence PIL 40/00371 to E.J. Johns and P1L40/4062 to J.L. Marshall. Male Wistar rats, 270C325?g, were obtained from Charles River (Kent) and after one week acclimatization in the animal holding facility were anaesthetized with sodium pentobarbitone, 60?mg?kg?1 i.p., and the trachea cannulated to ensure a patent airway. A cannula was placed in the right carotid artery to measure systemic blood pressure (Spectramed Statham, Oxnard CA, U.S.A., transducer linked to a Grass Model 7E polygraph) and a further cannula was inserted into the right femoral vein to allow infusion of pentobarbitone at a rate of 15?mg?kg?1?h?1 (1?ml?h?1) to maintain a constant plane of anaesthesia. The right femoral artery was also cannulated with fine tubing (PP10), the end of which was extruded, and this was inserted until the fine tip just entered the left renal artery. It was kept patent by means of a constant infusion of saline (150?mM NaCl) at 5?ml?h?1 (Braun Perfusor, Melsungen, Germany) and allowed direct intra-renal arterial administration of drugs. The left kidney was exposed a mid-line abdominal incision, the renal artery was carefully isolated and an electromagnetic flow probe placed on it to allow a direct monitoring of renal blood flow (Carolina Medical Electronics Inc., King, NC, U.S.A., EP100 series flow probe linked to a FM 501 flowmeter). The animals were allowed 90C120?min to recover from the surgical procedures. Drugs given intra-renal arterially (i.r.a.) were injected in a volume of 30?l into the femoral arterial line a self-sealing rubber insert, and then flushed into the kidney by the saline infusion. Once the new stable Apelin agonist 1 level of renal blood flow had been achieved (within 5C10?min) readings of flow and blood pressure were taken before the subsequent dose of compound was given. The endothelins have a very long duration of action, extending into hours, consequently cumulative dose-response curves were generated. Drugs Endothelin-1, endothelin-3 and sarafotoxin 6c were obtained from Sigma-Aldrich (Poole, Dorset, U.K.). Stock solutions were made up at 1?mg?ml?1 and aliquots stored deep frozen until required. Dilutions to the appropriate concentrations were made with saline. Cumulative dose-response curves ranged from 1C1000?ng i.r.a. and in some studies up to 5000?ng i.r.a. The endothelin.