Acute kidney injury (AKI) due to ischemia-reperfusion (I/R) insult involves oxidative stress and inflammation leading to rapid renal decline and remains a significant cause of post-operative mortality. Myristoylated protein kinase C beta II peptide inhibitor (N-myr-SLNPEWNET; myr-PKCβII-) is known to attenuate myocardial I/R injury in ex vivo rat hearts. We hypothesized that myr-PKCβII- would attenuate severe renal I/R injury that is characterized by elevated serum creatinine (Cr) and a decrease in glomerular filtration rate (GFR). We predict that treatment with myr-PKCβII- will improve these indices of kidney function compared to a scrambled control peptide (N-myr-WNPESLNTE; myr-PKCβII-scram). Renal pedicles of anesthetized male C57BL/6J mice (25-30g) were clamped bilaterally for 20 min or 19 min. Five minutes before unclamping, 2.0 mg/kg (20 µM serum) myr-PKCβII- or myr-PKCβII-scram were given i.v. into the tail vein. Cr (mg/dL) was measured at baseline, 24h, 72h, and 96h post-injury. GFR (µl/min) was determined with fluorescein-isothiocyanate (FITC)-Sinistrin renal clearance. Data were evaluated by unpaired Student's t-test. Following 20-min renal ischemia (Fig 1.), myr-PKCβII- (n=9) significantly reduced Cr at 24h and 72h post-injury compared to myr-PKCβII-scram control (n=8, p<0.05). However, there were three fatalities prior to 96h. In 19-min ischemia, there were no fatalities up to 96h post-injury. However, Cr levels of the myr-PKCβII-scram control (n=8) in 19-min I/R were significantly lower than 20-min I/R at all time points post-injury (all p<0.01): 24h (0.54 ± 0.10 vs 1.59 ± 0.06 mg/dL), 72h (0.24 ± 0.06 vs 1.28 ± 0.25 mg/dL), and 96h (0.17 ± 0.03 vs 0.72 ± 0.15 mg/dL). Myr-PKCβII- did not significantly reduce Cr (Fig. 1) nor improve GFR (Fig. 2) following 19-min I/R. Results suggest that 20-min renal ischemia was more severe, which was indicated by a 5-fold increase of peak Cr levels at 72h post-injury compared to 19-min ischemia and the unanticipated fatalities of three mice. Myr-PKCβII- attenuated renal injury following 20-min renal ischemia, but not at the milder 19-min model in which peak Cr levels were too low to detect therapeutic benefit. The large difference in injury severity between 20-min and 19-min renal ischemia emphasizes the temporal relationship between renal function and ischemic duration. Future studies will characterize myr-PKCβII- protection against AKI in 19-min bilateral renal ischemia based on biomarkers indicating proximal renal tubule damage (e.g. NGAL and Kim-1). A more optimal ischemic duration between 19 min and 20 min will be investigated for future experiments.