Objectives: The nature of endothelial factors in response to acetylcholine (ACh) was investigated in conductance and resistance arteries from Lyon normotensive (LN) and Lyon hypertensive (LH) rats. Differences in endothelial function between the two strains were evaluated.
Methods and design: Relaxations to ACh were studied in the aorta and small mesenteric arteries (SMA). The relative contribution of nitric oxide (NO), prostanoids and endothelial-derived hyperpolarizing factor (EDHF) was assessed using appropriate inhibitors. Western blot of endothelial NO synthase was achieved. The membrane potential of smooth muscle cells was assessed using microelectrodes.
Results: In LN rats, endothelium-dependent relaxation to ACh involved exclusively NO in the aorta, whereas both NO and EDHF were implicated in SMA. In the latter, relaxation was almost entirely prevented by blockade of either the NO or EDHF pathway, although ACh was still able to produce hyperpolarization in the presence of NO synthase and cyclooxygenase inhibitors. In LH rats, relaxation to ACh was unchanged in SMA but moderately depressed in the aorta, despite unchanged endothelial NO synthase protein expression and sensitivity to NO. In addition, indomethacin, but not a selective cyclooxygenase-2 inhibitor, significantly reduced ACh relaxations in the aorta from LH rats but not from LN rats.
Conclusions: These results document differential endothelial function in a conductance and in resistance arteries from LN rats and LH rats. They show that simultaneous participation of NO and EDHF is required to promote relaxation in SMA from both strains, whereas NO alone accounts for relaxation in aorta from LN rats. In LH rats, aortic relaxation induced by ACh is slightly decreased despite the involvement of vasodilator products from cyclooxygenase-1.