Microinjection of nitroprusside into the nucleus tractus solitarius decreases cerebral blood flow in anesthetized rats

Abstract

Contributions of nitric oxide, EDHF, and EETs to endothelium-dependent relaxation in renal afferent arterioles.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.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).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.Acetylcholine-induced afferent arteriolar relaxation depends strongly on both nitric oxice, acting via soluble guanylate cyclase, and on an EDHF, likely 14,15-EET, acting via KCa.