Comparative relaxant effects of the NO donors sodium nitroprusside, DEA/NO and SPER/NO in rabbit carotid arteries.

1. Sodium nitroprusside (SNP, 10(-9)-3x10(-4) M), diethylamine/NO complex (DEA/NO, 10(-9)-10(-4) M) and spermine/NO complex (SPER/NO, 10(-8)-3x10(-4) M) induced concentration-dependent relaxation of isolated rabbit carotid arteries precontracted with KCl (50 mM) or with histamine (3x10(-6) M). 2. In KCl-precontracted arteries the order of potency was SNP=DEA/NO>SPER/NO, and in histamine-precontracted arteries the order of potency was SNP>DEA/NO>SPER/NO. Relaxations to the three NO donors were significantly higher in histamine-precontracted arteries than in KCl-precontracted arteries. 3. The guanylyl cyclase inhibitor methylene blue (10(-5) M) significantly inhibited relaxations to the three NO donors in histamine-precontracted arteries and, to a lesser extent, in KCl-precontracted arteries. 4. In conclusion, the NO donors SNP, DEA/NO and SPER/NO induce quantitatively different relaxation of rabbit carotid artery. Both, lower relaxant effects in depolarized arteries and inhibition of relaxation by methylene blue indicate the mediation of cGMP formation in the relaxant effects of the three NO donors.