Background: Type II diabetes in the Goto Kakizaki (GK) rats (derived from Wistar rats) is not associated with the development of obesity, hyperlipidemia, hypertension, or pronounced renal functional changes. The aim of this study was to investigate the effect of superimposed hypertension on renal function and morphology under conditions of hyper- and normoglycemia.
Methods: The evolution of biochemical and morphologic renal changes was examined in GK and Wistar rats treated with deoxycorticosterone acetate (DOCA) salt over 24 weeks.
Results: Blood pressure was increased from 6 weeks on in GK and Wistar rats with no difference in blood pressure levels between both groups (week 24, 183 +/- 14 mm Hg vs. 191 +/- 13 mm Hg, P = NS, vs. 144 +/- 6 mm Hg in normal controls, P < 0.01). A progressive increase in proteinuria was observed in hypertensive GK rats from 12 weeks on (week 24, 168 +/- 62 mg/day vs. 41 +/- 30 mg/day in hypertensive Wistar rats, P = 0.002). Histologic analysis at weeks 15 and 24 showed progressive glomerulosclerosis in hypertensive GK and Wistar rats (week 24, 13 +/- 4% vs. 8 +/- 1%, P = NS) but not in nonhypertensive GK controls. This was associated with evidence of podocyte damage (de novo desmin expression) in hypertensive as compared to nonhypertensive GK rats (week 24, score 1.4 +/- 0.1 vs. 0.8 +/- 0.1, P < 0.001) while no significant increase was observed in hypertensive vs. nonhypertensive Wistar rats. Tubulointerstitial damage was increased in hypertensive GK as compared to hypertensive Wistar rats (week 24, score 1.5 +/- 0.6 vs. 0.6 +/- 0.3, P = 0.01). By immunohistochemistry, this was associated with an up-regulation of tubulointerstitial type IV collagen as well as alpha-smooth muscle actin (alpha-SMA) expression, macrophage infiltration and cell proliferation in hypertensive GK rats.
Conclusion: Our data demonstrate that long-standing type II diabetes alone is not sufficient to induce progressive nephropathy unless secondary injurious mechanisms such as hypertension are present. The hypertensive GK rat provides a novel model to investigate the mechanisms involved in diabetic nephropathy.