DECREASED SENSITIVITY TO VASOCONSTRICTORS IN AORTIC RINGS AFTER ACUTEEXPOSURE TO NITRIC-OXIDE

Nitric oxide (NO) has been postulated as a regulator of vascular react ivity, and the current study tested the hypothesis that NO-induced dec reased sensitivity to vasoconstrictors persists following removal of N O. Endothelium-denuded segments of rat aorta were incubated 2-4 h at 3 7 degrees C with the NO donor S-nitroso-N-acetylpenicillamine (SNAP). Incubation produced rightward shifts in concentration response curves for phenylephrine [i.e., half-maximum effective concentration (EC(50); in mu M): control = 0.016, NO = 0.14], aluminum fluoride (i.e., EC(50 ) in mM: control = 1.66, NO = 2.29), and KCl (i.e., EC(50) in mM: cont rol = 5.9, NO = 23.9). Similar shifts were seen for two other NO donor s. The SNAP-induced shift was not attenuated by a guanylyl cyclase inh ibitor, LY-83583 (10 mu M) and was not mimicked by 8-bromoguanosine 3' , 5'-cyclic monophosphate (100 mu M). It was attenuated by 1,4-naphtho quinone (50 mu M), an inhibitor of endogenous mono-ADP ribosyltransfer ases. NO incubation increased cGMP content (4.6 +/- 0.8 vs. 1.5 +/- 0. 15 pmol/mg protein), an increase unaffected by 1,4-naphthoquinone (3.3 +/- 1.0 pmol/mg protein) but prevented by LY-83583 (1.6 +/- 0.36 pmol /mg protein). ADP ribosylation of three proteins was observed in membr anes from HEK 293 cells: 88, 66, and 38 kDa. ADP ribosylation of the 3 8-kDa protein was stimulated in a concentration-dependent manner by NO but was not decreased by 1,4-naphthoquinone. In conclusion, NO produc es a long-lasting inhibition of vascular contractility by both a cGMP- dependent and -independent mechanism. Based on the observations of 1,4 -naphthoquinone, we conclude that the cGMP-independent mechanism is no t stimulation of endogenous ADP ribosylation but some other covalent m odification in the pathway that mediates contraction.