Trying to explain an effect of "per se" hydrostatic pressure on heart rate in fish

Specific effects of "per se" hydrostatic pressure on mean heart rate have been studied on eels (Anguilla anguilla L.), both untreated and treated with atropine and propranolol, and on isolated eel's heart. Because temperature brings, by itself, heart rate modifications in fish, a quantitative study was performed in order to take away the increment of heart rate due to the water warming, which cannot entirely be suppressed during compression. The specific effects of "per se" pressure have been identified as a bradycardia above 24.5 degrees C and as a tachycardia below this temperature. The use of atropine and propranol, which abolish extrinsic heart control, shows that pressure acts both through extrinsic mechanisms of heart control and through a direct action on autonomic cardiac cells. This effect of "per se" pressure on cardiac cells is interpreted according to chemical kinetics laws. The hypothesis that pressure acts at the molecular level, possibly by the means of reversible structure modifications of some molecules, is suggested.