Distinct role of nitric oxide and endothelium-derived hyperpolarizing factor in renal microcirculation. Studies in the isolated perfused hydronephrotic kidney.
BACKGROUND
Both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) are established as important factors determining the vascular tone. The relative contribution of these factors to the renal microvascular tone, however, has not been delineated.


METHODS
Isolated perfused hydronephrotic rat kidneys were used to characterize the relative role of NO and EDHF in mediating the tone of interlobular arteries (ILA) and afferent arterioles (AFF).


RESULTS
During the norepinephrine constriction, acetylcholine (ACH, 1 micromol/l) induced a sustained vasodilation of ILA (90 +/- 9% reversal) and AFF (117 +/- 13% reversal). In the presence of nitro-L-arginine methylester (LNAME), the ACH-induced vasodilation of ILA and AFF was converted to transient dilation, with only 53 +/- 7 and 32 +/- 7% reversal observed 10 min after 1 micromol/l ACH (i.e sustained phase). In contrast, LNAME had no effect on the initial phase of ACH-induced dilation. In the presence of apamin + charybdotoxin, the initial vasodilator response to ACH (1 micromol/l) was diminished (ILA, from 108 +/- 8 to 46 +/- 9%; AFF, from 108 +/- 14 to 58 +/- 8%), whereas no impairment was observed in sustained phases. Furthermore, the magnitude of the vasoconstriction caused by LNAME was greater at smaller vessel segments. Finally, the LNAME-induced inhibition of the sustained phase of ACH-induced vasodilation was greater as the vessel diameter decreased.


CONCLUSIONS
That the relative contribution of NO and EDHF differs, with a greater role of NO in the basal tone and ACH-induced vasodilation at smaller vascular segments of ILA and AFF.
Ozawa
Yuri
Y
Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan.
Hayashi
Koichi
K
Nagahama
Takahiko
T
Fujiwara
Keiji
K
Kanda
Takeshi
T
Homma
Koichiro
K
Saruta
Takao
T
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001685:Biological Factors / Q000378:metabolism*; D018999:Charybdotoxin / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006869:Hydronephrosis / Q000378:metabolism; D066298:In Vitro Techniques; D007668:Kidney / Q000098:blood supply* / Q000378:metabolism; D008297:Male; D008833:Microcirculation / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D018999:Charybdotoxin; D001030:Apamin; D009569:Nitric Oxide; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine