EFFECTS OF HYPERTONIC SALINE ON MYOCARDIAL-FUNCTION AND METABOLISM IN NONISCHEMIC AND ISCHEMIC ISOLATED WORKING RAT HEARTS

Objective: To study the direct effects of hypertonic saline on the function of nonischemic and ischemic myocardium by the use of an isolated working rat heart model. Design: A prospective, randomized, controlled study, Setting: Animal laboratory at a university medical center, Subjects: Adult Wistar rats (n = 32) of both sexes. Interventions: The heart was excised via thoracotomy in anesthetized rats and prepared for antegrade perfusion at a constant heart rate in an antegrade perfusion apparatus at predetermined preloads and afterloads, Hearts were exposed to ischemia, ischemia followed by repeated hypertonic saline treatment, or repeated hypertonic saline without preceding ischemia, Myocardial ischemia was induced by decreasing the mean aortic pressure to 25 mm Hg, Measurements and Main Results: Variables that were measured or calculated included the following: left atrial pressure; mean aortic pressure; heart rate; coronary flow; aortic flow; cardiac output; stroke volume; Po-2, electrolyte content, osmolality, and lactate concentration of the perfusate and/or venous effluent; myocardial oxygen extraction; myocardial oxygen consumption; and myocardial lactate efflux, Ischemia resulted in pronounced impairment of myocardial function and metabolism, Hypertonic saline administration during ischemia induced an additional transient myocardial depression, In the nonischemic heart, a transient myocardial-depressant effect after hypertonic saline administration was also seen, Conclusions: The present results from an isolated working heart preparation show that hypertonic saline exerts myocardial-depressive effects in the ischemic as well as in the nonischemic heart, Systemic rather than direct myocardial effects may therefore be responsible for the previously reported beneficial hemodynamic effects of hypertonic saline in shock treatment.