ELECTROPHYSIOLOGICAL AND MECHANICAL-PROPERTIES OF ISOLATED RABBIT HEART PAPILLARY-MUSCLES AND THEIR CORRELATION WITH NITRIC-OXIDE (NO) AND OXYGEN-FREE RADICALS IN HYPOVOLEMIC SHOCK BLOOD-PLASMA

We investigated the electrophysiological and contractile responses of isolated rabbit heart papillary muscles, to plasma from the blood of r abbits suffering severe hypovolemic shock (SP) and compared the produc tion of oxygen free radicals and nitric oxide (NO) released as a resul t of the hypovolemic shock. Papillary muscles removed from the right h eart ventricle of 11 rabbits, superfused in an organ bath with oxygena ted (95% O-2 + 5% CO2) Tyrode solution at 37 degrees C were stimulated at a constant rate (1 Hz). The action potentials (APs) and contractio ns of papillary muscles were simultaneously recorded on a storage osci lloscope and photographed. SP exerted an intense negative inotropic ef fect on the papillary muscles accompanied by depression of the +V-max and prolongation of the fast and slow action potential duration. The e ffects of SP were reversible, to a large extent, when the extracellula r calcium concentration was increased from 1.8 to 3.6 and 5.4 mM, or a fter washout. The recovery was completed within 15 min. Furthermore, N O levels increased by 50 times and SP antioxidant capacity declined by 50%. These results indicate that SP contained humoral factors that pr omoted the production of oxygen free radicals and NO in hypovolemic sh ock. The neutralisation of NO by superoxide (O-2(-)) leads to the form ation of the noxious oxidant peroxynitrite (ONOO-) that may be respons ible for the observed excitation-contraction uncoupling.