Iloprost: a positive inotropic effect in isolated myocardium?: 091

Introduction: Iloprost, a stable derivate of prostacyclin (epoprostenol), is known to diminish PVR. In addition, improvement of right ventricular function has been observed after inhaled administration [¹]. Direct inotropic actions have not been studied until now. In the present experimental study the dose-dependent contractile response of human atrial and rabbit ventricular trabeculae to iloprost was investigated.

Method: 17 trabeculae from right atrial appendices and 25 preparations from rabbit right ventricle were studied. Developed force was continuously registered at a pacing frequency of 1 Hz at 37°C. Iloprost concentration was increased stepwise from 10⁻¹¹ to 10⁻⁷M. Results are given as mean ± SEM. Statistical analysis was performed by ANOVA for matched values.

Results: Baseline values were 8.52 ± 1.4mN/mm² for human trabeculae and 11.5 ± 1.5mN/mm² for rabbit trabeculae. Iloprost exerted a positive inotropic effect in 10 of 17 human trabeculae (“responders”). In 7 trabeculae no change in contractility was observed, despite a positive effect of recalcification. At higher concentrations after-contractions were seen in 29% of all human trabeculae. In 15 of 25 rabbit trabeculae iloprost increased contractility developed (“responders”), in 10 trabeculae no positive effect was achieved. After-contractions were not seen in rabbit trabeculae.

Table 1: Developed force in percent of baseline values at a Iloprost concentration of 10−9M.

Discussion: Our data suggest that iloprost exerts direct positive inotropic effects in a subset of human atrial and rabbit right ventricular trabeculae. However, species-independent, a relevant number of trabeculae did not respond to iloprost. Further investigations concerning the underlying mechanism of iloprost induced positive inotropism are necessary.