N,N,N-Trimethylsphingosine chloride (TMS), a stable N-methylated synthetic sphingolipid analogue, has been shown to modulate protein kinase C activity and exert a number of important biological effects, including: inhibition of tumor cell growth and metastasis, inhibition of leukocyte migration and respiratory burst, and inhibition of platelet aggregation. We hypothesized that TMS would be cytoprotective in clinically relevant in vivo murine models of myocardial and hepatic ischemia-reperfusion (I/R) injury. Wild-type, obese (ob/ob) and diabetic (db/db) mice were subjected to 30 min of left coronary artery occlusion followed by 24 hr of reperfusion in the myocardial I/R model. In additional studies mice were subjected to 45 min of hepatic artery occlusion followed by 5 hr of reperfusion. TMS was administered intravenously at the onset of ischemia. Myocardial infarct size, cardiac function and serum liver enzymes were measured to assess the extent of tissue injury. TMS attenuated myocardial infarct size by 66% in the wild-type and by 36% in the ob/ob mice. Furthermore, TMS reduced serum alanine transaminase levels by 43% in wild-type mice. These benefits did not extend to the ob/ob mice following hepatic I/R or to the db/db mice following both myocardial and hepatic I/R. A likely mechanism is the failure of TMS to inhibit PKC translocation in the diseased heart. This data suggests that although TMS is cytoprotective following I/R in normal animals, the cytoprotective actions of TMS are largely attenuated in obese and diabetic animals.