Long-term inhibition of nitric oxide synthase potentiates effects of anandamide in the rat mesenteric bed

In rat isolated mesenteric beds, anandamide induced a concentration-depende nt reduction (0.01-50 muM) of the contractile responses elicited by bolus a dministration of noradrenaline. The anandamide-induced reductions of noradr enaline responses were unmodified by the in vitro exposure to the nitric ox ide synthase (NOS) inhibitor, 100 muM L-N-G-nitro-L-arginine methyl ester ( L-NAME), whereas they were significantly potentiated after the long-term in vivo administration Of L-NAME (70 mg/kg/day during 4 weeks). Responses to anandamide were not potentiated and even reduced in mesenteric beds from ra ts made hypertensive by aortic coarctation. In mesenteric, beds isolated fr om either untreated or in vivo L-NAME treated rats, concentration-response curves to anandamide were significantly attenuated by the non-selective Kchannel blocker tetraethylammonium (TEA) but were not modified by either en dothelium removal, or the soluble guanylate cyclase inhibitor 1H-[1,2,4] ox adiazolo [4,3-a] quinoxalin-1-one (ODQ) or the cannabinoid receptor antagon ists 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl] (4-methoxyph enyl) methanone (AM630) and 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methy l-N-4-morpholinyl-1H-pyrazole-3-carboxamide (AM281). On the other hand, the vanilloid receptor agonist (E)-N-[4-hydroxy-3-methoxyphenyl)methyl]-8-meth yl-6-nonenamide (capsaicin) induced a concentration-dependent inhibition of noradrenaline-induced vasoconstriction, and the vanilloid receptor antagon ist N-[2-(4-chlorophenyl)ethyl]-1,3,4,5-tetrahydro-7,8-dihydroxy-2H-2-benza zepine-2-carbothioamide (capsazepine) caused a significant reduction of ana ndamide-induced responses in mesenteric beds isolated from both control and chronic L-NAME treated rats. The non-metabolizable analogue of anandamide, methanandamide, produced higher reductions of noradrenaline responses than anandamide in mesenteric beds isolated from controls but not from the L-NA ME treated rats. Moreover, in mesenteric beds from untreated but not from L -NAME treated rats, the effects of anandamide were significantly potentiate d by the inhibitor of endocannabinoid degradation, 200 muM phenylmethylsulp honyl fluoride (PMSF), and by the inhibitor of anandamide uptake, 5 muM (al l Z)-N-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM404). It is conclu ded that long-term inhibition of NOS potentiates anandamide-induced relaxat ions probably through changes in either endocannabinoid metabolism or uptak e. A possible compensatory role for endocannabinoids in vascular function i n situations in which nitric oxide (NO) synthesis is long-term impaired ari ses from the present results. (C) 2001 Elsevier Science B.V. All rights res erved.