cyclic-gmp and isoidide-dinitrate

1. We have shown previously that the D- and L- enantiomers of isoidide dinitrate (D-IIDN and L-IIDN) exhibit a potency difference for relaxation and cyclic GMP accumulation in isolated rat aorta and that this is related to preferential biotransformation of the more potent enantiomer (D-IIDN). The objective of the current study was to examine the effect of the flavoprotein inhibitor, diphenyleneiodonium sulphate (DPI), on the enantioselectivity of IIDN action. 2. In isolated rat aortic strip preparations, exposure to 0.3 microM DPI resulted in a 3.6 fold increase in the EC50 value for D-IIDN-induced relaxation, but had no effect on L-IIDN-induced relaxation. 3. Incubation of aortic strips with 2 microM D- or L-IIDN for 5 min resulted in significantly more D-isoidide mononitrate formed (5.0 +/- 1.5 pmol mg protein(-1)) than L-isoidide mononitrate (2.1 +/- 0.7 pmol mg protein(-1)) and this difference was abolished by pretreatment of tissues with 0.3 microM DPI. DPI had no effect on glutathione S-transferase (GST) activity or GSH-dependent biotransformation of D- or L-IIDN in the 105,000 x g supernatant fraction of rat aorta. 4. Consistent with both the relaxation and biotransformation data, treatment of tissues with 0.3 microM DPI significantly inhibited D-IIDN-induced cyclic GMP accumulation, but had no effect on L-IIDN-induced cyclic GMP accumulation. 5. In the intact animal, 2 mg kg(-1) DPI significantly inhibited the pharmacokinetic and haemodynamic properties of D-IIDN, but had no effect L-IIDN. 6. These data suggest that the basis for the potency difference for relaxation by the two enantiomers is preferential biotransformation of D-IIDN to NO, by an enzyme that is inhibited by DPI. Given that DPI binds to and inhibits NADPH-cytochrome P450 reductase, the data are consistent with a role for the cytochromes P450-NADPH-cytochrome P450 reductase system in this enantioselective biotransformation process.

Topics: Aged; Animals; Aorta, Thoracic; Biotransformation; Blood Pressure; Cyclic GMP; Glutathione Transferase; Hemodynamics; Humans; Hypoglycemic Agents; In Vitro Techniques; Male; Muscle Relaxation; Onium Compounds; Rats; Rats, Sprague-Dawley; Stereoisomerism; Sugar Alcohols; Vasodilator Agents

Previously, it was shown that the D enantiomer of isoidide dinitrate was 10-fold more potent than the L enantiomer and 10-fold less potent than glyceryl trinitrate for stimulating cyclic GMP accumulation and relaxation of isolated rat aorta. In the present study, these organic nitrates were tested for their ability to induce tolerance to organic nitrate-induced relaxation, cyclic GMP accumulation, and guanylate cyclase activation in rat aorta in vitro. To compensate for the differences in vasodilator potency, tolerance was induced by incubating isolated rat aorta with concentrations of organic nitrates 1,000-fold greater than the EC50 for relaxation. Under these conditions, the EC50 for relaxation was increased significantly for each organic nitrate and to a similar degree on subsequent reexposure. These data suggest that the potential for inducing in vitro tolerance to relaxation was the same for the three organic nitrates tested. When activation of soluble guanylate cyclase by these compounds was assessed, the enantiomers of isoidide dinitrate were equipotent, but less potent than glyceryl trinitrate, suggesting that the site of enantioselectivity is not guanylate cyclase itself. In blood vessels made tolerant to organic nitrates by pretreatment with glyceryl trinitrate, vasodilator activity, cyclic GMP accumulation, and guanylate cyclase activation were attenuated on reexposure to each organic nitrate. In addition, differences in the potency of the three organic nitrates and the enantioselectivity of isoidide dinitrate for relaxation were abolished in tolerant tissue, whereas the potency difference between glyceryl trinitrate and isoidide dinitrate for activation of guanylate cyclase was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Aorta; Cyclic GMP; Dose-Response Relationship, Drug; Drug Tolerance; Guanylate Cyclase; Male; Muscle, Smooth, Vascular; Nitrates; Nitroglycerin; Rats; Rats, Inbred Strains; Stereoisomerism; Sugar Alcohols; Vasodilation