Objective: To determine whether sphingomyelinase pathway activation would participate in myocardial depression induced by endotoxin.
Design: Randomized, controlled trial.
Setting: Experimental laboratory.
Subjects: Male Sprague-Dawley rats, isolated rat heart, and cardiac myocytes.
Interventions: Cardiovascular function was evaluated in rats injected with saline, endotoxin (10 mg/kg, intravenously), and N-oleoylethanolamine (NOE; 10 mg/kg, intravenously). In ex vivo experiments, isolated rat hearts were perfused with endotoxin (5 microg/mL). For pharmacologic intervention, NOE (1 micromol/L) was admixed to the perfusate 20 mins before endotoxin. In in vitro experiments, ventricular myocytes were incubated with sphingosine (20 microM). Myocyte cell shortening and calcium transient were measured. Mitochondrial membrane potential was measured using the cationic dye tetramethylrhodamine methylester fluorescence technique.
Measurements and main results: Endotoxin treatment at 4 hrs did not alter mean arterial pressure and abdominal blood flow compared with control rats. Left ventricle developed pressure (LVDP) and its first derivatives (i.e., maximal and minimal change in pressure over time [dP/dtmax and dP/dtmin]) were decreased after 4 hrs in endotoxin-treated rats compared with control rats. NOE (10 mg/kg) treatment largely prevented left ventricular systolic function alterations of endotoxin-treated hearts (n = 6 in each group). In isolated rat heart, endotoxin (5 microg/mL) caused increases in tumor necrosis factor-alpha perfusate concentration and delayed depression of LVDP, dP/dtmax, and dP/dtmin after 60 mins, which was partially abrogated in the presence of the ceramidase inhibitor NOE (1 micromol/L). Sphingosine (20 microM) caused decreases in cell fractional shortening, calcium transient, and mitochondrial membrane potential of cardiac myocytes.
Conclusion: These observations suggest that the sphingomyelinase pathway participates in endotoxin-induced myocardial depression.