Cytochemical effect of a stable PGI2 analog iloprost on guinea-pig heart in calcium-free and calcium paradox conditions

Morphological and cytochemical effects of stable prostacyclin analog, iloprost were studied on isolated and perfused guinea-pig hearts according to Langendorff in Ca-free and Ca paradox conditions. Samples from the papillary muscles and left ventricular wall-muscles were examined. For calcium cytochemistry lead acetate and potassium pyroantimonate, and for nickel cytochemistry dimethylglyoxime (DMG) techniques were used. Electron microscopic studies showed that during Ca-free perfusion (for 15 min) and the following Ca repletion (for 15 min) disruption of the sarcolemma, damages in the sarcotubular system and in the mitochondria and gradual separation of intercalated discs were observed. Treatment with iloprost (1 microM) prevented those alterations in Ca-free and Ca paradox conditions. Iloprost caused a change in the intracellular distribution of Ca2+, decreased the cytochemically-demonstrated calcium in the cytoplasma, and inhibited the formation of calcium phosphate granules in mitochondria. Iloprost did not modify the number of nickel-DMG complexes either in Ca-free or in Ca paradox conditions. This study indicates that iloprost prevents the morphological damages caused by Ca paradox. The study also suggests that iloprost has an effect on the intracellular handling of calcium.

Generation of NO from molsidomine (SIN-1) in vitro and its relationship to changes in coronary vessel tone

The release of NO from SIN-1, the active metabolite of molsidomine, was measured in vitro in Langendorff-perfused rabbit hearts. NO in the coronary effluent was determined on-line using the oxyhemoglobin technique. Left ventricular and coronary perfusion pressure were also recorded continuously. Glyceryl trinitrate and iloprost were used as reference compounds. Infusion of SIN-1 or glyceryl trinitrate into the coronary inflow resulted in a significant and dose-dependent NO release. An apparently identical response was seen when SIN-1 was infused into the coronary effluent while the response to glyceryl trinitrate was greatly reduced or abolished. The glyceryl trinitrate-induced coronary vasodilation was only slightly diminished in presence of oxyhemoglobin whereas the response to SIN-1 was abolished. This is explained by complete scavenging of NO by oxyhemoglobin within the vessel lumen. In isolated porcine aortic endothelial cells, SIN-1 induced a significant and dose-dependent increase in cyclic GMP, whereas glyceryl trinitrate was ineffective. This would argue against biotransformation of glyceryl trinitrate to NO by endothelial cells. Finally, glyceryl trinitrate-tolerant heart preparations exhibited a considerably reduced or even undetectable release of NO, whereas the response to SIN-1 was unchanged.