Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA358

Poster Communications

Activation of the lactate receptor, GPR81, alters renal vascular function by direct and indirect mechanisms

N. K. Jones1, K. Wallenius2, K. Stewart1, J. W. Wiseman3, J. J. Mullins1, M. A. Bailey1

1. BHF Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, United Kingdom. 2. CVRM, IMED Biotech Unit, AstraZeneca R&D, Gothenburg, Sweden. 3. Discovery Sciences, IMED Biotech Unit, AstraZeneca R&D, Gothenburg, Sweden.

  • Table 1: EC50 values from non-linear dose response curves in isolated vessel segments from C57BL/6J mice. Vessels were treated with either vehicle or 30μM GPR81 agonist, AZ'5538 prior to preconstriction with phenylephrine. Cumulative dose response curves for acetylcholine (ACH) and sodium nitroprusside (SNP) are shown as mean±SD (n=8 for all). Two-way ANOVA was performed; significant P values are highlighted in red.

G protein-coupled receptor 81 (GPR81) is highly expressed in adipocytes and activation by the endogenous ligand lactate or by the specific agonist AZ'55381 inhibits lipolysis. The receptor is also found in non-adipose tissue2 but the function here is not well understood; recent studies show that GPR81 activation increases blood pressure1 (BP). Here, we screened for GPR81 expression in the kidney and vasculature and used AZ'5538 to assess the effect of GPR81 activation on BP and renal haemodynamics in vivo. End point PCR confirmed expression of GPR81 in kidney, aorta, mesenteric, renal and interlobar arteries taken from adult male C57BL/6J mice (n=4) culled by cervical dislocation. Other mice (n=6) were anaesthetised with Inactin (120mg/kg IP), the jugular vein cannulated for IV infusion (0.2ml/h/10g) of a) 5% mannitol vehicle and b) AZ'5538 (250μM over 15 mins). BP was recorded via the carotid artery. Data are mean±SD. AZ'5538 increased SBP by 14.9±6.5mmHg, whereas the vehicle had no significant effect (0.7±3.1mmHg). The pressor effect of AZ'5538 was absent in GPR81 null mice (n=4), confirming on-target action. In separate experiments, renal blood flow was measured by a Doppler ultrasound probe placed around the left renal artery or by pulse-wave Doppler ultrasound in anaesthetised mice (n=4). Renal blood flow was decreased compared to vehicle control in both studies (-0.33±0.23mL/min vs vehicle 0.04±0.02ml/min,P=0.027 and -185±25mm/s vs vehicle -0.4±20mm/s, P<0.01, respectively). Next, activation of GPR81 was assessed ex vivo by wire myography. Vessel segments were incubated with 30μM AZ'5538 for 15 minutes (n=8 for all). Renal arteries showed significant vasoconstriction (19.7±13.9% of maximal response to high potassium salt solution, P<0.01 against vehicle by two-way ANOVA); mesenteric arteries and the aorta showed no changes in tone. In all vessels incubated with GPR81 agonist, the response to the endothelium dependent vasodilator acetylcholine was blunted but responses to the nitric oxide donor sodium nitroprusside were not (Table 1). This shows that GPR81 activation influences vascular function and renal haemodynamics by both direct and indirect mechanisms. The sensitivity of the renal circulation to GPR81 activation may become physiologically significant when lactate concentration rises, as can occur in renal disease.

Where applicable, experiments conform with Society ethical requirements