Differential biotransformation of glyceryl trinitrate by red blood cell-supernatant fraction and pulmonary vein homogenate.
We have demonstrated previously that glyceryl trinitrate (GTN) undergoes biotransformation to two glyceryl dinitrate (GDN) metabolites in the human red blood cell-supernatant fraction (RBC-SF) by hemoglobin-mediated and sulfhydryl-dependent enzymatic mechanisms. In the present study, we have shown that biotransformation of GTN in rabbit RBC-SF yields a glyceryl-1,2-dinitrate (1,2-GDN)/glyceryl-1,3-dinitrate (1,3-GDN) ratio of 5.3. Following inhibition of hemoglobin-mediated biotransformation of GTN by carbon monoxide (CO), the 1,2-GDN/1,3-GDN ratio was 2.1. Following inhibition of sulfhydryl-dependent biotransformation by N-ethylmaleimide (NEM), the 1,2-GDN/1,3-GDN ratio was 30.0. We have demonstrated previously that for GTN-induced vasodilation of isolated bovine pulmonary vein (BPV), the 1,2-GDN/1,3-GDN ratio was 7.1, which indicated that a hemoprotein-dependent process was involved in GTN biotransformation. To determine if this was the case, the biotransformation of GTN (0.51 microM) was studied in BPV homogenates; 31.1 pmol GDN/mg BPV protein was formed in 20 min. The 1,2-GDN/1,3-GDN ratio was 1.1, which indicated that hemoprotein-mediated biotransformation did not occur. This conclusion was supported by the fact that CO did not inhibit GTN biotransformation. GTN biotransformation by BPV homogenate was inhibited 62% by NEM, 89% by boiling of the homogenate, and almost completely by boiling plus NEM. These results indicated that biotransformation of GTN by the BPV homogenate involved in a combination of enzymatic and nonenzymatic processes that were mostly sulfhydryl dependent. It is concluded that the mechanism for GTN biotransformation in isolated intact BPV, which yielded preferential formation of 1,2-GDN, was rendered nonfunctional upon tissue homogenization.
Marks
G S
GS
Department of Pharmacology and Toxicology, Faculty of Medicine, Queen's University, Kingston, Ont., Canada.
McLaughlin
B E
BE
MacMillan
H F
HF
Nakatsu
K
K
Brien
J F
JF
D000818:Animals; D001711:Biotransformation; D002417:Cattle; D002855:Chromatography, Thin Layer; D004912:Erythrocytes / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D005996:Nitroglycerin / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D011667:Pulmonary Veins / Q000378:metabolism; D011817:Rabbits
C014509:dinitroglycerol; D005996:Nitroglycerin