Differences in renal outcomes with ACE inhibitors in type 1 and type 2 diabetic patients: Possible explanations

In type 1 diabetic patients, ACE inhibitors exert a renoprotective effect w hich appears to be additional to, but not entirely independent of, changes in systemic blood pressure. This effect includes attenuation of albumin exc retion rate (AER) as well as prevention or slowing of the rate of decline o f the glomerular filtration rate (GFR). In type 2 diabetic patients, the re sults of ACE inhibition are more varied with some studies showing similar r eno-protection to that observed in type I diabetes and others showing no ad ditional effect to lowering of systemic blood pressure. This may be due to the diverse manifestations of the disease itself or to renal factors which may modify the response to ACE inhibitors. The major sytemic causes of dive rsity are variations in age, race and blood pressure. The major renal cause s of diversity include changes in the relationship or 'coupling' of AER to onset of decline in GFR and a heterogeneity of renal ultrastructural change s in the glomeruli, tubules, interstitium and the renal vasculature. Factor s that may be responsible for different renal responses to ACE inhibitors i n type 2 diabetes include coexistence of coronary heart disease which may i ntroduce survival bias in long-term studies, a lower specificity of microal buminuria for diabetic nephropathy, early onset of a decline in GFR in hype rtensive or normotensive patients at or prior to the onset of microalbuminu ria, a greater contribution of arteriosclerotic changes in renal arteries t o decline in renal function, a higher prevalence of nondiabetic renal disea se, a higher prevalence of hypertension in the elderly and yet to be charac terized genetic factors. These variants of type 2 diabetes may be expected to influence the response to ACE inhibitors either by altering the initial proteinuric response or by altering the hypotensive response. Future studie s taking into account the above variables may help to determine the relativ e importance of the above factors in modifying the renal responses to ACE i nhibitors and thereby leading to different renal outcomes in type 1 and typ e 2 diabetic patients. Such studies may also help to assess the relative im portance of changes in systemic blood pressure and intrarenal effects as we ll as the role of hemodynamic versus structural factors in contributing to differences in renal outcome with,ACE inhibitors in type 1 and type 2 diabe tes.