The Effect of Nitroglycerin on the Gravid Uterus in Sheep and Rabbits

Abstract

Clinical reports suggest that nitroglycerin (TNG) has an effect on the uterus that is detected by the obstetrician on palpation, but not obvious by measurement of uterine pressure. This study was designed to compare the effects of TNG on uterine compliance and tension. We used three sets of experiments to evaluate the effect of TNG on the uterus. In vivo experiments were conducted on laboring ewes and rabbits 2 h postpartum to measure the effect of TNG on active uterine tension. An in vitro experiment was also conducted by using isolated uterine strips from term pregnant rabbits to evaluate the effect of TNG on uterine compliance. TNG had no discernible effect on uterine intracavitary pressure or frequency of contraction in either laboring ewes or postpartum rabbits at doses that were sufficient to reduce the mean arterial pressure. TNG did, however, increase the compliance of uterine tissue from rabbits at term, whereas S-nitroso-N-acetylpenicillamine failed to produce a similar effect. Thus, the perceived relaxant effects of TNG may be caused by an increase in uterine compliance, which may facilitate efforts by the obstetrician to manipulate the uterus. While the mechanism of action remains unclear, it appears to be independent of nitric oxide. The administration of nitroglycerin may have a relaxant effect on the uterus. These experiments were conducted to elucidate the effect of nitroglycerin on the peripartum uterus by measuring active tension and compliance.