Preserved cardiovascular homeostasis despite blunted acetylcholine‐induced dilation in mice with endothelial muscarinic M3 receptor deletion

Aim: Muscarinic acetylcholine receptors (AChMR1‐5) are fundamental for cellular responses upon release of the neurotransmitter acetylcholine (ACh) from parasym- pathetic nerve fibers. ACh is the prototypical agonist stimulating endothelium‐de- pendent dilation, but most blood vessels lack parasympathetic innervation, raising the question as to the physiologic function of endothelial AChMR in vivo. Global deletion of AChM3R revealed a role in ACh‐induced vasodilation in vitro and food uptake, but overall cardiovascular homeostasis has not been examined thoroughly. Methods: To characterize the function of endothelial AChM3R in vivo, we deleted AChM3R specifically in endothelial cells with an inducible or a non‐inducible Cre‐ loxP system, driven by the endothelium‐specific promoters VE‐cadherin (indEC‐ M3R−/−)orTIE2(tek2;EC‐M3R−/−) and examined arteriolar dilation in the cre- master microcirculation, arterial pressure and cardiac function in these mice in vivo. Results: In both EC‐M3R−/−, ACh‐induced dilation was strongly impaired in arterioles in vivo, while responses to other dilators were mostly preserved. How- ever, arterial pressure (indEC‐M3R−/−) and arteriolar tone as a surrogate for peripheral vascular resistance did not differ between EC‐M3R−/− and control mice. Aged EC‐M3R−/− mice (74‐78 weeks) did not differ in body weight, heart weight, cardiac structure or contractile function from controls. Conclusion: We conclude that AChM3R elicits the endothelium‐dependent dila- tion upon ACh also in arterioles in vivo. Despite this prominent role, the endothe- lial deletion of AChM3R does not affect overall cardiovascular homeostasis. Thus, their physiologic function in endothelial cells remains obscure.