To the Editor: The article by Panza et al. (July 5 issue)1 reported an impairment of endothelium-dependent vascular relaxation induced by acetylcholine in patients with essential hypertension. In the Discussion section the authors argued against the possibility of a role for hyperpolarizing factor in this observed phenomenon. However, hyperpolarizing factor is also a relaxing factor released by acetylcholine,2 probably acting on a different subtype of muscarinic receptor.3 It has been speculated that this factor may play a part in the endothelium-dependent response to acetylcholine.3 It might be possible to study the endothelial relaxing factor or factors that mediate the different.
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