Primary acute sympathetic activation (PASA) can increase arterial pressure (AP). Under this situation, the kidneys may receive mutually opposing influences from sympathetic activation: a direct anti-diuretic effect via the renal innervation and pressure diuresis. We examined whether PASA would reduce urine output regardless of the AP elevation. We also examined the impact of renal denervation (RDN) on urine output during PASA. The experiment was performed on rats 3 to 9 days after unilateral RDN (n = 10). Under anesthesia, systemic sympathetic nerve activity (SNA) was varied over a wide range via the carotid sinus baroreflex. The slope of urine flow versus SNA was positive (0.252 ± 0.052 μL·min-1·kg-1· %-1) on the intact side, and it was greater on the denervated side (0.331 ± 0.069 μL·min-1·kg-1· %-1, P < 0.05). In conclusion, urine output change was an effect of elevated AP during PASA. Nevertheless, RDN was able to augment pressure diuresis during PASA.