Characterisation of the response to ADP in porcine isolated pancreatic arteries

Mouhamed Alsaqati, S. L. F. Chan, V. Ralevic. Nottingham Uinversity, Nottingham, UK

Adenosine-5’-diphosphate (ADP) and other nucleotides may play an important role in regulating blood flow in tissues, the effects of which are dependent on the receptors (and their isoforms) expressed in the vasculature. ADP has been shown to induce vasorelaxation, by acting at P2Y1 purine receptors on the endothelium (Erlinge & Burnstock., 2008) or by a mechanism involving activation of adenosine receptors on vascular smooth muscle cells (Rayment et al., 2007). However, little is known about the effects of ADP in pancreatic blood vessels. The aim of the current study was to examine the effects of ADP on vasotone and its mechanism of action in porcine isolated pancreatic arteries. Segments of porcine pancreatic arteries were prepared for isometric tension recording in warmed oxygenated Krebs-Henseleit buffer, the pigs were young adults, aged 9-10 months, body weight was 50-60 kg, and the majority of them were males. ADP (1 µM-1 mM) was added cumulatively after preconstriction with U46619, a thromboxane A2-mimetic. The ADP responses were investigated in the absence and presence of a P2Y1-selective antagonist, MRS 2179 (50 µM), and a non-selective adenosine receptor antagonist, XAC (10 µM). All the drugs were dissolved in distilled water, while U46619 was made up as a 10-2 stock in ethanol. In some preparations, the endothelium was removed by gently rubbing the innermost surface of the artery with forceps. Statistical analysis was carried out using two-way ANOVA. Data are presented as mean ± s.e.m. Relaxations were expressed as a percentage of the U46619-induced contraction. ADP induced concentration-dependent relaxation in pancreatic arteries maximum response was 65 ± 6%, mean EC50 value was 55 µM (95% confidence interval (CI). This relaxation was blocked by MRS 2179 (maximum response to ADP + MRS2179 was 50 ± 12%, P<0.01, n = 7). In addition, the ADP response was inhibited by XAC (maximum response to ADP + XAC was 23 ± 7.5%, P<0.001, n = 9). Removal of the endothelium inhibited the relaxation evoked by ADP by a similar extent as MRS 2179 (maximum response to ADP after the endothelium being removed was 44.5 ± 4.5%, P<0.001, n = 12). These results suggest that, in porcine isolated pancreatic arteries, ADP mediates vasorelaxation largely via actions at adenosine receptors, but additionally via P2Y1 receptors. Quantitatively similar inhibition of ADP-induced relaxations by endothelium removal and MRS 2179 suggests that the P2Y1 receptors may be located on the endothelium, and the adenosine receptors on the smooth muscle.

Erlinge, D, Burnstock, G (2008) Purinergic Signal 4(1): 1-20.

Rayment, SJ, Ralevic, V, Cordell, R, Alexander, SP (2007) FASEB J 21(2): 577-585.