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

Objective: To study the direct effects of hypertonic saline on the fun ction of nonischemic and ischemic myocardium by the use of an isolated working rat heart model. Design: A prospective, randomized, controlle d study, Setting: Animal laboratory at a university medical center, Su bjects: Adult Wistar rats (n = 32) of both sexes. Interventions: The h eart was excised via thoracotomy in anesthetized rats and prepared for antegrade perfusion at a constant heart rate in an antegrade perfusio n apparatus at predetermined preloads and afterloads, Hearts were expo sed to ischemia, ischemia followed by repeated hypertonic saline treat ment, or repeated hypertonic saline without preceding ischemia, Myocar dial 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; stro ke volume; Po-2, electrolyte content, osmolality, and lactate concentr ation of the perfusate and/or venous effluent; myocardial oxygen extra ction; myocardial oxygen consumption; and myocardial lactate efflux, I schemia resulted in pronounced impairment of myocardial function and m etabolism, Hypertonic saline administration during ischemia induced an additional transient myocardial depression, In the nonischemic heart, a transient myocardial-depressant effect after hypertonic saline admi nistration was also seen, Conclusions: The present results from an iso lated working heart preparation show that hypertonic saline exerts myo cardial-depressive effects in the ischemic as well as in the nonischem ic heart, Systemic rather than direct myocardial effects may therefore be responsible for the previously reported beneficial hemodynamic eff ects of hypertonic saline in shock treatment.