In vivo mechanisms of acetylcholine-induced vasodilation in rat sciatic nerve.
We examined the importance of nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and neurogenic activity in agonist-induced vasodilation and baseline blood flow [i.e., nerve microvascular conductance (NMVC)] in rat sciatic nerve using laser Doppler flowmetry. Agonists were acetylcholine (ACh) and 3-morpholinosydnonimine (SIN-1). Vasodilation occurring despite NO synthase (NOS) and cyclooxygenase inhibition and showing dependence on K(+) channel activity was taken as being mediated by EDHF. NOS and cyclooxygenase inhibition with N(omega)-nitro-L-arginine (L-NNA) + indomethacin (Indo) revealed two phases of ACh-induced vasodilation: an initial, transient L-NNA + Indo-resistant vasodilation, peaking at 23 +/- 6 s and lasting 145 +/- 69 s, followed by sustained L-NNA + Indo-sensitive vasodilation. L-NNA alone did not affect sustained ACh-induced vasodilation but decreased baseline NMVC by 55%. In the presence of L-NNA + Indo, the K(+) channel blocker tetraethylammonium (TEA) inhibited transient ACh-induced vasodilation by 58% and reduced baseline NMVC by 25%. SIN-1-induced vasodilation increased fourfold in the presence of L-NNA, whereas the specific guanylyl cyclase inhibitor 1H-(1, 2, 4)oxadiazolo(4,3-alpha)quinoxalin-1-one abolished it. However, in homogenates of rat sciatic nerve, SIN-1-stimulated soluble guanylyl cyclase (sGC) activity was unaffected by L-NNA. TTX affected neither SIN-1- nor ACh-induced vasodilation. In conclusion, ACh-induced vasodilation consisted of two components, the first partially mediated by EDHF and the second by a vasodilatory prostanoid + NO. Baseline NMVC was dependent on NO and EDHF. Although L-NNA enhanced SIN-1-induced vasodilation, it had no effect on sGC-activity.
Thomsen
K
K
Department of Medical Physiology, University of Copenhagen, DK-2200 Copenhagen N, Denmark. kthomsen@mfi.ku.dk
Rubin
I
I
Lauritzen
M
M
D000109:Acetylcholine / Q000378:metabolism* / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001685:Biological Factors / Q000378:metabolism / Q000494:pharmacology; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism; D017078:Laser-Doppler Flowmetry; D008297:Male; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D019335:Nitroarginine; D009569:Nitric Oxide; D013779:Tetrodotoxin; C002385:linsidomine; D008981:Molsidomine; D019001:Nitric Oxide Synthase; D006162:Guanylate Cyclase; D000109:Acetylcholine