Contributions of nitric oxide, EDHF, and EETs to endothelium-dependent relaxation in renal afferent arterioles.
BACKGROUND
Acetylcholine-induced endothelium-dependent relaxation in the renal afferent arteriole has been ascribed to nitric oxide, but the role of endothelium-derived hyperpolarizing factors (EDHFs) and 14,15-epoxyeicosatrienoic acid (14,15-EET) are unclear.


METHODS
Single afferent arterioles were dissected from kidney of normal rabbits and microperfused in vitro at 60 mm Hg. Vessels were preconstricted submaximally with norepinephrine (10(-8) mol/L). Relaxation was assessed following cumulative addition of ACh (10(-9) to 10(-4) mol/L) alone, or in the presence of indomethacin (to inhibit cyclooxygenase), Nw-nitro-L-arginine (L-NNA) (to inhibit nitric oxide synthase), methylene blue (to inhibit soluble guanylate cyclase), or a combination of L-NNA + methylene blue. To assess contributions by EDHF, studies were repeated with either apamin + charybdotoxin [to block Ca2+-activated K+ channels (KCa)] or with 40 mmol/L KCl. To asses the role of 14,15-EET, relaxations were evaluated in the presence of its competitive inhibitor 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE).


RESULTS
Relaxation by acetylcholine was abolished following endothelial denudation. It was unaffected by indomethacin but was inhibited 54%+/- 5% (P < 0.001) by L-NNA, 57%+/- 5% by methylene blue, and 60%+/- 4% by the combination of L-NNA plus methylene blue. Relaxation was inhibited further by KCl (80%+/- 6%) or by apamin + charybdotoxin (96%+/- 2%). 14,15-EEZE, alone, inhibited acetylcholine-induced relaxation by 29%+/- 3%, and by 80%+/- 5% in the presence of L-NNA.


CONCLUSIONS
Acetylcholine-induced afferent arteriolar relaxation depends strongly on both nitric oxide, acting via soluble guanylate cyclase, and on an EDHF, likely 14,15-EET, acting via KCa.
Wang
Dan
D
Division of Nephrology and Hypertension, Center for Renal Disease and Hypertension Research, Department of Medicine, Georgetown University, Washington, D.C. 20007, USA.
Borrego-Conde
Lillian J
LJ
Falck
John R
JR
Sharma
Kamalesh K
KK
Wilcox
Christopher S
CS
Umans
Jason G
JG
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000378:metabolism*; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D001685:Biological Factors / Q000378:metabolism*; D018999:Charybdotoxin / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019335:Nitroarginine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors; D011817:Rabbits; D012079:Renal Circulation / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D004791:Enzyme Inhibitors; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D018999:Charybdotoxin; D009599:Nitroprusside; D019335:Nitroarginine; D001030:Apamin; D009569:Nitric Oxide; C046782:14,15-epoxy-5,8,11-eicosatrienoic acid; D015126:8,11,14-Eicosatrienoic Acid; D000109:Acetylcholine