Autoregulation of Glomerular Filtration Rate in Patients With Type 1 Diabetes During Spironolactone Therapy

Double-masked, randomized, crossover trial. In random order, patients will be treated with spironolactone 25 mg o.d. and matched placebo for 28 days. On the last day of treatment, GFR will be determined twice on the same day: first without clonidine and secondly after injection of clonidine (clonidine induces a transient reduction in blood pressure, with no influence on renal plasma flow and GFR), in order to evaluate the effect of antihypertensive treatment with spironolactone on renal autoregulation of GFR. The study will be preceded by a wash-out period of 1 month for patients receiving antihypertensive medication. Patients will be instructed to measure blood pressure twice daily, three days a week during this period. If, during the washout period, blood pressure exceeds 170/105 mm Hg or persistent edemas develop, treatment with long-acting loop diuretics will be initiated and continued throughout the rest of the study. If blood pressure despite diuretic treatment still exceeds 170 mm Hg systolic and/or 105 mm Hg diastolic, the patient will be excluded from the study and previous/appropriate antihypertensive treatment will be restarted.