The metabolic fate of nitroglycerin (trinitrin) in relation to its vascular effects

The metabolism of nitroglycerin (trinitrin) was studied in dogs and rabbits. After intravenous injection of nitroglycerin in either species, plasma levels immediately declined and then gradually increased; maximum plasma levels occurred between 10 and 20 min after injection. This peculiar course of the plasma levels was due to redistribution of the drug in different organs. The blood pressure responses to nitroglycerin did not parallel the plasma levels. Pretreatment of rabbits with SKF 525 A, an enzyme inhibitor, or with phenobarbital, an enzyme inducer, markedly influenced the plasma levels but did not affect the vascular effects of nitroglycerin. After oral administration of nitroglycerin, blood pressure was normal despite high plasma levels. The vascular effects of nitroglycerin did not seem to be determined by its metabolism or plasma levels.