Effect of contractile agents on vasorelaxation to oleoylethanolamide in isolated aortic rings from spontaneously hypertensive rats

Amanda Wheal, Stephen Alexander, Michael Randall. University of Nottingham, Nottingham, United Kingdom.

N-Oleoylethanolamide (OEA) is a fatty acid amide with structural similarity to the endocannabinoid anandamide. Anandamide causes an enhanced fall in mean arterial pressure, in anaesthetised spontaneously hypertensive rats (SHR) compared to normotensive controls (Wistar Kyoto rats (WKY)) (Bátaki et al. 2004). In addition, we have previously reported that anandamide caused an enhanced vasorelaxation in isolated aortic rings taken from SHR compared to WKY (Wheal et al. 2009). In light of these observations, and that OEA causes vasorelaxation in isolated aortae taken from Wistar rats (Wheal et al. 2008), this study aimed to determine the vasorelaxant responses to OEA in this model of hypertension in vitro.
Aortic rings, taken from male SHR (228-300 g) and WKY (237-320 g), were mounted in a myograph and bathed in warmed (37 °C), gassed (95% O2 / 5% CO2) modified Krebs-Henseleit solution. Preparations were pre-tensioned to 9.8 mN. After 1 h equilibration, the preparations were contracted with either methoxamine (WKY 9.8 ± 1.3 μM n=20; SHR 26 ± 8.1 μM n=16) or 100 nM U46619. Once a stable tone was achieved, time controls and concentration-response curves to OEA were constructed.

Vessels were either contracted using methoxamine (WKY induced tension = 18.3 ± 1.1 mN n=20; SHR induced tension=16.8±0.8mN n=16) or the thromboxane A2 analogue U46619 (100 nM) (WKY induced tension = 18.1 ± 1.5 mN n=20; SHR induced tension = 25.3 ± 1.9 mN n=8). OEA caused a concentration-dependent vasorelaxation in aortae contracted using methoxamine. This vasorelaxation, reached a greater maximum in SHR than WKY (Rmax WKY =15 ± 2 % (n=10); SHR = 49 ± 5 % (n=8)) (P<0.0001, unpaired Students’ t-test), despite a similar potency in both strains (pEC50 WKY = 8.2 ± 0.3 (n=10); SHR = 8.0 ± 0.3 (n=8)). In preparations contracted with U46619, there was no difference between the vasorelaxation of OEA-administered preparations and the time controls in either strain (Rmax for WKY time control = 6 ± 2 % (n=5); WKY OEA response = 15 ± 11 % (n=5); SHR time control = 9 ± 7 % at 100 min (n=4); SHR OEA response = 10 ± 4 % (n=4)).

This study has shown that OEA causes vasorelaxation in thoracic aorta, which is greater in SHR than WKY, and of similar magnitude to the responses obtained by Wheal et al. (2009) using anandamide. In addition, contractions of aortae from SHR were more reactive to U46619 than WKY, but neither strain caused vasorelaxation to OEA when contracted with this spasmogen.

Bátkai et al. (2004).Circulation 110: 1996–2002.
Wheal AJ, Randall MD. (2009). Eur J Pharmacol. 603 (1-3):79-85.
Wheal AJ et al. (2008) http://www.pA2online.org/abstracts/Vol6Issue4abst120P.pdf

This work was funded by the British Heart Foundation.