Renal function studies in diabetic nephropathy

Glucose transporters: cellular links to hyperglycemia in insulin resistance and diabetes

Abnormal expression and/or function of mammalian hexose transporters contribute to the hallmark hyperglycemia of diabetes. Due to different roles in glucose handling, various organ systems possess specific transporters that may be affected during the diabetic state. Diabetes has been associated with higher rates of intestinal glucose transport, paralleled by increased expression of both active and facilitative transporters and a shift in the location of transporters within the enterocyte, events that occur independent of intestinal hyperplasia and hyperglycemia. Peripheral tissues also exhibit deregulated glucose transport in the diabetic state, most notably defective translocation of transporters to the plasma membrane and reduced capacity to clear glucose from the bloodstream. Expression of renal active and facilitative glucose transporters increases as a result of diabetes, leading to elevated rates of glucose reabsorption. However, this may be a natural response designed to combat elevated blood glucose concentrations and not necessarily a direct effect of insulin deficiency. Functional foods and nutraceuticals, by modulation of glucose transporter activity, represent a potential dietary tool to aid in the management of hyperglycemia and diabetes.

Diabetic renal disease: the quest for normotension--and beyond

Over the past two decades there has been an increasing interest in hypertension as a risk factor for diabetic renal disease and in particular for the possibility of early antihypertensive intervention. Therefore, it would seem timely to review the history of hypertension in diabetes, with special reference to renal disease and the need for normotension, in a manner resembling glycaemic control. Elevated blood pressure (BP) associated with diabetes mellitus has been recognized since the beginning of the century and was initially particularly documented in association with the demonstration of the striking histological lesion in glomeruli, starting with the observation of Kimmelstiel and Wilson in 1936. These patients in many cases also showed hypertension, as confirmed in several subsequent reports, very similar to the studies of Kimmelstiel and Wilson. However, the development was hampered by the lack of effective antihypertensive agents and also by some who believed that elevated BP could be of importance to preserve renal function in these individuals. Indeed, it was suggested that reduction of BP could mean permanent deterioration in renal function. BP remained very high in the standard care of diabetic patients up to the middle 1970s. At this time it was documented that elevated BP was very closely related to development of diabetic renal disease in Type 1 (insulin-dependent) diabetic (IDDM) patients, and studies also showed a correlation between blood pressure and rate of progression. This correlation stimulated research in intervention, and indeed in the 1980s and 1990s several long-term studies reported that antihypertensive treatment can reduce the rate of decline in glomerular filtration rate (GFR) from about 12 ml min-1 yr-1 down to about 2 ml min-1 yr-1 in the most optimistic reports; usually a mean level of 2-5 ml min-1 yr-1 is achievable by antihypertensive treatment, in clinical situations where glycaemic control often is far from perfect. Many studies have also documented that BP starts to rise in the early phase of incipient diabetic nephropathy characterized by microalbuminuria. This is a stage with well-preserved GFR and therefore probably an ideal stage for intervention in these at risk patients. Many studies, in particular those employing angiotensin converting enzyme (ACE) inhibitors based on important pathophysiological concepts proposed by Brenner, have shown that microalbuminuria can be reduced or stabilized by early antihypertensive treatment, just as we see with optimized glycaemic control. ACE inhibitors have also been widely used in patients with overt nephropathy and the rate of decline in GFR has been reduced considerably.(ABSTRACT TRUNCATED AT 400 WORDS)

Prognostic implications of renal hypertrophy in diabetes mellitus

Early in the course of type 1 diabetes mellitus, hypertrophy of the kidney is a consistent finding that is easily diagnosed using current noninvasive methods, especially ultrasonography. Renal functional changes occur in association with hypertrophy, most notably glomerular hyperfiltration. The structural counterpart of this functional change is an early increase in capillary filtration surface area. In most forms of nondiabetic renal hypertrophy, kidney size is closely linked to GFR. In contrast, in diabetes, persistence of hypertrophy after the clinical onset of overt kidney disease (microalbuminuria, hypertension, decreased GFR, etc.) suggests that sustained release of one or more growth factors may continue even after kidney function declines. The fact that growth factors can act in both an autocrine and paracrine fashion raises the possibility that the local effects of such substances may act as local mediators of kidney growth. Failure of renal hypertrophy to reverse following strict glycemic control for a few months may turn out to be an important prognostic indicator of future progression of the renal disease, but this remains to be established. Prospective studies of kidney size in patients with newly diagnosed type 1 diabetes, using accurate noninvasive methods, may be helpful in establishing whether irreversible ("autonomous") hypertrophy of the kidney is indeed a useful prognostic indicator. As therapies are developed that target the different microvascular complications of diabetes (retinopathy, nephropathy, neuropathy), a noninvasive estimation of kidney size may be a cost-effective method of predicting ultimate renal involvement. Since microalbuminuria occurs relatively late in the disease process, early and persistent hypertrophy of the kidney may become a useful prognostic test in the earliest stages of the disease.

Renal extraction ratios for 51Cr-EDTA, PAH, and glucose in early insulin-dependent diabetic patients

Renal clearances and extraction ratios for 51Cr-EDTA and PAH were studied in six young patients with insulin-dependent diabetes. The duration of the disease was 1 to 4 years, and no patient had signs of diabetic complications. Catheterization of the right renal vein and the left brachial artery was performed. The extraction ratios for 51Cr-EDTA, PAH, and glucose were determined at two different levels of blood glucose. Clearance for 51Cr-EDTA was increased by 9.7% and for PAH by 8.5% compared to normal control subjects while the extraction ratios for 51Cr-EDTA and PAH were normal. Extraction ratio for glucose was very low. There was no correlation between the individual HbA1 values and the clearances for 51Cr-EDTA and PAH. Extraction ratios for these substances were not influenced by acute changes in blood glucose level. The normal PAH extraction ratio indicates that PAH clearance is a reliable estimate of RPF in early insulin-dependent diabetes.

Glomerular filtration rate and renal plasma flow in long-term juvenile diabetics without proteinuria

Glomerular filtration rate and renal plasma flow were examined in 16 young male non-proteinuric diabetics (mean age 28.4 years) with a duration of diabetes of over 15 years (mean duration 21.5 years.) In this selected group of long-term diabetics the glomerular filtration rate was clearly increased, the mean being 136 ml/min (+/-S.D. 11.8) (normal value 114 ml/min (+/-14.1), being comparable to that found earlier in short-term diabetics. There was no change in renal plasma flow. It is concluded that kidney function is generally well preserved in long-term diabetics who have not developed proteinuria.