Characteristics of renal tubular atrophy in experimental renovascular hypertension: A model of kidney hibernation

The inability to separate irreversible lesions of tubular epithelia from reversible tubular atrophy constitutes a major problem in histopathology and in decisions for revascularization of shrunken kidneys with renal artery stenosis. In order to characterize reversible tubular atrophy ('kidney hibernation') we studied the physiological and biochemical parameters and morphology including histochemistry in rat kidneys made atrophic by renal artery stenosis and treatment with the angiotensin-converting enzyme inhibitor, enalapril. Renal artery stenosis was induced by a 0.2-mm clip around the left renal artery. Following 7 weeks of clipping and 2 concomitant weeks of enalapril treatment, the kidney length decreased from 17.8 +/- 0.3 to 13.7 +/- 0.7 mm (mean +/- SEM). Renal blood flow and glomerular filtration rate decreased to 39 +/- 3% and to approximately 3% of control values, respectively. The activities of the intracellular proteolytic enzymes cathepsin B and L and of Na-K-ATPase in microdissected proximal tubular segments decreased to values below 50 and 10%, respectively. All changes were significant (p < 0.05). Histochemical staining for ATPase activity in the distal tubule segments remained unchanged. Tubular cells were atrophic but not necrotic. Histochemical staining of alkaline phosphatase in the tubular brush border and of acid phosphatase and peroxidase in lysosomes was greatly reduced. All observed changes were reversible within 2-3 weeks following removal of the clip and withdrawal of enalapril either with or without contralateral nephrectomy. Thus, a form of kidney hibernation with readily reversible tubular atrophy has been described. Based on this description it may be possible in consecutive experiments to differentiate between reversible and irreversible tubular atrophy.