Influence of the renal medulla and early treatment with enalapril upon the development of hypertension in young spontaneously hypertensive rats.

OBJECTIVE: To investigate the role of the renal medulla in early hypertension in spontaneously hypertensive rats (SHR), and to explore whether the attenuated increase of pressure induced by enalapril treatment is affected by chemical medullectomy. DESIGN: Forty-four male SHR were studied from 5 to 18 weeks of age: 22 remained intact; 22 were medullectomized at 5.5 weeks of age with 2-bromoethylamine hydrobromide; 11 of each of these two groups were treated with enalapril from 6 to 12 weeks of age. Blood pressure, heart rate and body weight were recorded intermittently, and at 18 weeks renal function was also analysed. RESULTS: The results indicate a protective effect of the renal medulla against severe pressure rises in SHR, although even when enalapril also lowered blood pressure in medullectomized SHR, persistent improvements of glomerular filtration rate and renal flow conductance occurred only in intact SHR. Furthermore, after enalapril treatment ended blood pressure rose to higher levels in medullectomized SHR, despite greater sodium-water losses. CONCLUSION: The renal medulla seems to exert a protective role both during and after enalapril treatment.