Angiogenesis inhibitors are effective anti-cancer agents, but also cause hypertension and renal injury. Earlier, we observed in rats that high-dose aspirin (capable of blocking cyclooxygenase (COX)-1 and -2) prevented these side effects better than low-dose aspirin (blocking COX-1 only). Therefore, we hypothesized that selective COX-2 inhibition would prevent toxicity during angiogenesis inhibition, and that this toxicity involves a reduced ratio of vasodilator/constrictor COX-derived prostanoids, i.e., prostacyclin (PGI 2 ) and thromboxane (TXA 2 ). Male WKY rats received vehicle, angiogenesis inhibition (sunitinib (SU), 14 mg/kg/day) alone or combined with COX-2 inhibition (celecoxib, 10mg/kg/day), a PGI 2 analogue (iloprost 100 μg/kg/day), or a dual TXA 2 synthase/receptor antagonist (picotamide, 2.5 mg/kg/day) for 8 days (n=7-8/group). Mean arterial pressure (MAP) was measured via radiotelemetry, vascular function was assessed via wire myography, and biochemical measurements were performed by ELISA. SU induced a rapid increase in MAP (16±2 vs. 3±1 mmHg after vehicle on day 6, P<0.001), which was blunted by celecoxib (10±2 mmHg on day 6, P=0.06 versus SU), temporarily attenuated by iloprost (on treatment days 1-2) and unaffected by picotamide. Wire myography demonstrated a trend towards increased vasoconstrictor response to endothelin-1 in iliac arteries after SU, which was prevented by celecoxib (P<0.001). SU increased albuminuria (0.6±0.1 vs. 0.3±0.1 mg/24h after vehicle; P<0.001), and this was prevented by celecoxib only (0.4±0.1 mg/24h, P=0.01 vs. SU). SU increased the PGI 2 /TXA 2 ratio in both plasma (2.7±1.2 vs. 0.6±0.2 after vehicle, P=0.05) and urine (22±2.2 vs. 0.9±0.2 after vehicle, P<0.001). In conclusion, selective COX-2 inhibition combats angiogenesis inhibitor-induced hypertension and renal toxicity. SU paradoxically increases the PGI 2 /TXA 2 ratio, particularly in the kidney. Although this upregulation might initially be protective, it could eventually contribute to renal toxicity, most likely because PGI 2 exerts deleterious effects in excessive concentrations. Targeting excessive renal PGI 2 production might be another promising strategy to prevent renal toxicity during angiogenesis inhibition.