Inotropic and chronotropic effects of isoprenaline in rats exposed to 30 bar

Inotropic and chronotropic responses to the beta-agonist, isoprenaline (ISO) were studied with a transducer located in the left ventricle and a catheter placed in the left femoral artery in anesthetized rats at 1 and 30 bar. The hemodynamic control values were equal in both series. During ISO infusion the chronotropy increased equally (34%) at 1 and 30 bar. The inotropy increased by 38% during ISO infusion at 1 bar (Series 1). Increased inotropy (44%), and unchanged chronotropy were found during compression to 30 bar (Series 2). The ISO evoked inotropic responses in absolute values were greater at 30 bar than at 1 bar. Nevertheless, an equal relative (%) increase in inotropy was found during ISO infusion at 30 bar compared to 1 bar. The cardiac oxygen consumption was estimated to be 65% higher at 30 bar during ISO infusion compared to that at 1 bar.