Increased urinary C-type natriuretic peptide excretion may be an early marker of renal tubulointerstitial fibrosis

► The histological changes began to emerge since 72 h after UUO. ► The cortical thickness decreased time-dependently in UUO rats. ► The increased UP was the earliest biochemical abnormality in UUO rats. ► Urinary CNP excretion significantly enhanced in UUO rats compared to SOR. ► Urinary CNP excretion was negatively correlated with UP, BUN and Cr.