HYPERTONIC SALINE IS A NEGATIVE INOTROPIC AGENT IN NORMOVOLUMIC DOGS

The inotropic effects of hypertonic saline (HS) and hyperosmotic dextrose (HD; 2,400 mosmol/l, 4 ml/kg) were determined in normovolumic, chloralose-anesthetized, intact (n = 14) and autonomically blocked (n = 8) dogs. Solutions were infused intravenously over 3 min. HS and HD rapidly increased preload in both intact and autonomically blocked dogs, as assessed by significant (P < 0.05) increases in plasma volume, end-diastolic volume, and end-diastolic pressure. In intact dogs, HS produced a nonsignificant decrease in end-systolic elastance (E(es)) and a nonsignificant increase in the maximal rate of change of left ventricular pressure (dP/dt(max)) and cardiac output, whereas HD produced a significant increase in E(es), dP/dt(max), and cardiac output. In autonomically blocked dogs, HS significantly decreased E(es) and significantly increased dP/dt(max) but did not alter cardiac output, whereas HD significantly increased E(es), dP/dt(max), and cardiac output. We conclude that in normovolumic animals, HS is a negative inotropic agent, HD is a positive inotropic agent, and the in vivo effect of an ionic hyperosmotic agent (HS) differs from that of a nonionic hyperosmotic agent (HD).