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.