Receptor-mediated contraction of aortic valve leaflets

The mechanisms that regulate the function of the aortic valve are not fully understood. Cusp tissue has been shown to have contractile properties, but little is known as to which receptors mediate these effects.

We have examined, using isolated organ baths, the response of porcine aortic valve leaflets to a range of vasoactive agents including endothelin-1, noradrenaline, adrenaline, the thromboxane (TX) A2 mimetic U46619, 5-hydroxytryptamine (5-HT), histamine and angiotensin II. The viability of each individual leaflet was tested by the addition of 90 mM KCl.

All agents tested, with the exception of angiotensin II, were capable of inducing concentration-dependent contractions of the valve leaflets. The responses to endothelin-1 and U46619 were significantly greater than those of all the other agents tested. Responses to endothelin-1 could be inhibited by 10(-5) M of the mixed ET(A/B) receptor antagonist bosantan. The response to both catecholamines was blocked by 10(-6) M yohimbine, but not by 3 x 10(-7) M prazosin, indicating the presence of alpha2-adrenoceptors. The response to histamine was mediated exclusively by H1-receptors, as judged by the antagonistic effect of 10(-6) M of the H1-receptor antagonist mepyramine. The response to 5-HT could be blocked by 10(-6) M of the 5-HT2A-receptor antagonist ketanserin, and that of U46619 by 10(-6) M of the TXA2-receptor antagonist SQ30741.

These results demonstrate the range of receptor systems that can mediate contraction of aortic valve leaflets. Further studies are required to elucidate the role of these receptors in the physiology and pathophysiology of the aortic valve.