Gamma irradiation induces acetylcholine-evoked, endothelium-independent relaxation and activates K-channels of isolated pulmonary artery of rats.
OBJECTIVE
To test the effects of irradiation (R*) on the pulmonary artery (PA).


METHODS
Isolated PA rings were submitted to gamma irradiation (cesium, 8 Gy/min(-1)) at doses of 20 Gy-140 Gy. Rings were placed in an organ chamber, contracted with serotonin (10(-4) M 5-hydroxytryptamine [5-HT]), then exposed to acetylcholine (ACh) in incremental concentrations. Smooth muscle cell (SMC) membrane potential was measured with microelectrodes.


RESULTS
A high dose of irradiation (60 Gy) increased 5HT contraction by 20%, whereas lower (20 Gy) doses slightly decreased it compared with control. In the absence of the endothelium, 5-HT precontracted rings exposed to 20 Gy irradiation developed a dose-dependent relaxation induced by acetylcholine (EI-ACh) with maximal relaxation of 60 +/- 17% (n = 13). This was totally blocked by L-NAME (10(-4) M), partly by 7-nitro indazole; it was abolished by hypoxia and iberiotoxin, decreased by tetra-ethyl-ammonium, and not affected by free radical scavengers. In irradiated rings, hypoxia induced a slight contraction which was never observed in control rings. No differences in SMC membrane potential were observed between irradiated and nonirradiated PA rings.


CONCLUSIONS
Irradiation mediates endothelium independent relaxation by a mechanism involving the nitric oxide pathway and K-channels.
Eder
Veronique
V
Laboratoire de Physiopathologie de la Paroi Artérielle, Faculté de Médecine, Université François Rabelais, Tours, France. eder@med.univ-tours.fr
Gautier
Mathieu
M
Boissière
Julien
J
Girardin
Catherine
C
Rebocho
Manuel
M
Bonnet
Pierre
P
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002586:Cesium; D004730:Endothelium, Vascular / Q000187:drug effects / Q000528:radiation effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005720:Gamma Rays; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000528:radiation effects; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D015221:Potassium Channels / Q000502:physiology / Q000528:radiation effects*; D011651:Pulmonary Artery / Q000187:drug effects / Q000528:radiation effects*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000528:radiation effects; D014664:Vasodilation
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D002586:Cesium; D012701:Serotonin; D019001:Nitric Oxide Synthase; D000109:Acetylcholine