Influence of nitric oxide on hemodynamic changes induced by intravenous administration of hypertonic saline dextran (HSD) in anesthetized dogs *
A small volume of HSD has been shown to improve circulation after massive hemorrhage and severe burns in human and animal studies. Common findings after a bolus infusion of HSD arc rapid restoration of cardiac output and an improvement in peripheral circulation. Some mechanisms by which HSD increases cardiac output have been proposed : intravascular volume expansion caused by a body fluid shift from intracellular space, dilatation of blood vessels, and increased cardiac contractility. However, the exact mechanisms are still under investigation. In the present study, we examined the influence of nitric oxide (NO) on hemodynamic changes induced by abolus infusion of HSD in anesthetized dogs. Twelve mongrel dogs were divided into two groups : a control group (n =6) and an L-NMMA group (n =6) . The L-NMMA group received L-NMMA (1 mg/kg) in 100 ml of normal saline for 30 min, while the control group received only 100 ml of normal saline. Before and after infusion of L-NMMA, hemodynamics and cardiac contractility using the left ventricular end-systolic pressure-volume relationship were measured. Then, a bolus of HSD (4 ml/kg iv) was given to the groups, and hemodynamic measurements were repeated during the experimental period : before HSD infusion. 30 sec after the infusion, 1 min, 3 min, 5 min, and 10 min after infusion. NO was also measured before HSD infusion and 10 min after the infusion. The infusion of L-NMMA increased systemic vascular resistance (SVR) in the L-NMMA group significantly as compared with the control group. Other hemodynamic parameters including heart rate (HR) , blood pressure (BP) and cardiac output (CO) were similar in the groups. After the infusion of HSD, there were no changes in SVR, BP, and CO between the groups. However, a significant but small increase in HR was found in the L-NMMA group. Cardiac contractile changes in the groups did not differ significantly. The sum of nitrate and nitrite concentrations in arterial blood was also insignificant between the groups before and after the infusion of HSD. The present findings suggest that NO may not play a major role in HSD-induced hemodynamic changes. (Accepted on October 30, 1999) Kawasaki Igakkaishi 25(4) : 297-306, 1999
