RENAL EFFECTS OF CALCIUM-ANTAGONISTS IN DIABETES-MELLITUS - AN OVERVIEW OF STUDIES IN ANIMAL-MODELS AND IN HUMANS

A number of studies based on animal models of both diabetes and renal insufficiency have shown that adequately reducing blood pressure attenuates the progression of glomerulosclerosis and decreases urinary protein excretion. Furthermore, compared with conventional antihypertensive therapy, angiotensin converting enzyme (ACE) inhibitors show a greater benefit in reducing these parameters. Nineteen published animal studies have investigated the effects of calcium antagonists on renal hemodynamics and glomerulosclerosis, but only three of them have evaluated the use of calcium antagonists with models of diabetes. Of six micropuncture studies based on a 1 5/6 nephrectomy model of renal insufficiency, five demonstrated reduced efferent arteriolar resistance, two showed reduced glomerular capillary pressure (P(GC)), and two showed significantly reduced proteinuria and glomerulosclerosis. Studies using nifedipine with both the unilaterally nephrectomized DOCA salt rat model and the 1 5/6 nephrectomy model demonstrated reduced proteinuria and glomerulosclerosis that was independent of reduced P(GC). Two separate micropuncture studies of the spontaneously hypertensive rat model also found reduced efferent arteriolar resistance and P(GC) as well as proteinuria. Finally, studies of Dahl "salt-sensitive" rats showed an early decrease in glomerulosclerosis without a significant change in either proteinuria or glomerulosclerosis after five weeks. The results of eleven clinical studies of diabetic patients have been published; they showed divergent effects of calcium antagonists on renal function and urinary protein excretion. In the various animal models, the divergent renal hemodynamic and histologic effects reported for calcium antagonists may be largely due to the equality of blood pressure reduction, the varied baseline hemodynamic profiles, and the divergent status of the renin-angiotensin system. In humans, the disparate effects may be related to the stage of diabetes investigated as well as to the above-mentioned factors.