Arterial contraction studies

Animals were culled by cervical dislocation according to Schedule 1 procedure approved by the UK Home Office. Mesenteric arcades were dissected out and placed immediately into ice-cold Krebs solution (125 mM NaCl, 3.8 mM KCl, 1.2 mM CaCl₂, 25 mM NaHCO₃, 1.2 mM KH₂PO₄, 1.5 mM MgSO₄, 0.02 mM EDTA and 8 mM d-glucose, pH 7.4). Second-order mesenteric, saphenous or carotid arteries were cleaned of fat and connective tissue under a dissection microscope. Segments of 1 mm length were mounted in an isometric wire myograph system (Multi Wire Myograph System, 620 M), bathed with Krebs solution warmed at 37 °C and gassed with 95% O₂/5% CO₂ then stretched stepwise radially to their optimum resting level to an equivalent transmural pressure of 100 mm Hg and equilibrated for 1 h prior to experiments. For studies of luminal flow in second-order mesenteric artery, vessel segments were mounted on glass cannulas in a pressure myograph (Model 110p, Danish Myo Technology A/S, Denmark). Flow was generated by increasing the pressure difference (ΔP) between inflow and outflow without change in the absolute intraluminal pressure. The outer arterial diameter was monitored using a CCD camera (DMX41 AU02, Imaging Source Europe, Germany) and recorded with MyoView II software. Arteries were only used for investigation if they constricted in response to phenylephrine (PE) and dilated in response to acetylcholine (ACh).