Effect of infusion administration set on the delivery rate and plasma concentration of nitroglycerin in dogs

Tissue distribution of glyceryl trinitrate and the effect on cGMP levels in rat

In order to study distribution in tissue, rats were treated subcutaneously with glyceryl trinitrate, GTN, (50 mg/kg). The concentrations of GTN were measured in plasma, brain, heart, adipose tissue and aortic tissue at different sampling times by a gas chromatographic method with electron-capture detection. The peak GTN-concentration was reached after 2 hours in all tissues examined. The highest concentration of GTN was found in adipose tissue, where the level was approximately forty times higher than in plasma. The concentration of GTN in brain, heart and aortic tissue was about 2-3 times as high as in plasma. The cGMP level was measured in heart and brain. An increase of the cGMP level was found in brain 2 hours after GTN administration. No cGMP increase was found in heart tissue. The results indicate a substantial distribution of GTN to tissue, and an increase of cGMP in brain. The distribution of the substance in the tissues as shown, might have both pharmacokinetic and pharmacodynamic implications.

Pharmacokinetics and pharmacodynamics of organic nitrates

The pharmacokinetic and pharmacodynamic aspects of organic nitrates are discussed, with particular emphasis on the 3 major organic nitrates currently in use, nitroglycerin (NTG), isosorbide dinitrate and isosorbide-5-mononitrate. After intravenous administration, both NTG and isosorbide dinitrate exhibit large systemic clearances and both nitrates appear to be extensively distributed in vascular and other peripheral tissues. Two pharmacokinetic features appear particularly notable for NTG: there is a significant arteriovenous extraction of the drug, and its systemic clearance is related to cardiac output. Both of these features, plus other evidence, suggest that organic nitrates may be substantially removed from the systemic circulation by the vasculature itself. During nitrate tolerance, plasma drug concentrations remain elevated, but vascular activity is diminished. This apparent paradox might be explainable by a unifying hypothesis of reduced nitrate metabolism during vascular tolerance; thus, in the tolerant state, reduced systemic clearance of the intact drug brought about elevated plasma concentrations, whereas reduced cellular metabolism at the smooth muscle brought about a decrease in vascular activity. The complex relations among plasma kinetics, vascular metabolism and pharmacologic action of organic nitrates are still poorly understood.

Retention and subsequent liberation of glyceryl trinitrate in organ baths influences the relaxation of bovine mesenteric arteries contracted by various agents

The present study compares the relaxant effect of glyceryl trinitrate (GTN) on isolated bovine mesenteric artery in commonly used organ baths made of glass and in disposable vials made of polyethylene, a material known to be inert to GTN. It is shown that the EC50-value for the GTN-induced relaxation is about 1000-fold lower when polyethylene vials are used. The study also shows that the reason for this is that the materials previously used in the experimental equipment retain and subsequently liberate GTN at re-use. In organ baths of glass with holders of acrylics, GTN concentrations of about 20 nM were found during equilibration, i.e. before start of the experiment. The vessel specimens become partly tolerant during equilibration in such organ baths and thus the vessels are less sensitive to GTN. The findings may explain the discrepancy between previous in vitro and in vivo studies. Low concentrations known to be effective in vivo have not been demonstrated to have a relaxant effect in earlier in vitro studies.