Renal hemodynamic effects of captopril and doxazosin during slight physical activity in hypertensive patients with type-1 diabetes mellitus

Angiotensin-converting enzyme inhibitors are renoprotective in diabetes mel litus through their intrarenal hemodynamic effects. Alpha-1 blockade has va riable pre-and postglomerular vasodilatory effects dependent upon the stimu lation of the sympathetic nervous system. We tested the hypothesis that the two different classes of drugs have similar renal hemodynamic effects when the patients are examined in an upright position where the sympathetic ner vous system is activated. Mean blood pressure (MAP), glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were examined in 28 hyper tensive type-1 diabetic patients with variable degree of nephropathy treate d for a mean period of 7.6 +/- 0.4 months with captopril (n = 13) or doxazo sin (n = 15). Average treatment doses were 112 +/- 7 mg/day in the captopri l group and 8 +/- 1 mg/day in the doxazosin group. Sitting MAP decreased fr om 118 +/- 3 to 106 +/- 4 mm Hg after captopril (p < 0.05), and from 117 +/ - 4 to 110 +/- 3 mm Hg after doxazosin (p = 0.07). GFR and ERPF were unchan ged in both groups. The filtration fraction (FF) decreased from 0.27 +/- 0. 02 to 0.25 +/- 0.02 after captopril (p < 0.05) and from 0.26 +/- 0.01 to 0. 25 +/- 0.01 after doxazosin (p = 0.08). Calculation of 95% confidence inter vats of the difference between the post-treatment values as well as the di fference between pre- and post-treatment values of MAP, GFR, ERPF and FF of the two drugs indicates no difference in renal hemodynamic response betwee n the drugs. In conclusion, captopril and doxazosin have similar renal hemo dynamic responses when the patients are examined in a situation where the s ympathetic nervous system is stimulated, and this suggests that doxazosin h as a renoprotective effect beyond the blood pressure-lowering effect. Copyr ight (C) 2001 S. Karger AG, Basel.