Urine volume and urinary albumin excretion in the study groups. Changes in (A) urine volume and (B) urinary albumin excretion of LETO rats and OLETF rats treated with either sildenafil (OLETF-SIL) or vehicle (OLETF-CON) are shown. Data are means ± SEM. Mann–Whitney test: *P < 0.05, **P < 0.01, ***P < 0.001: LETO vs. OLETF-CON; #P < 0.05, ##P < 0.01: OLETF-SIL vs. OLETF-CON. LETO, Long-Evans Tokushima Otsuka; OLETF, Otsuka Long-Evans Tokushima Fatty.