Induction of insulin resistance in normal adipose tissue by uremic human serum

Exploring Adiposity and Chronic Kidney Disease: Clinical Implications, Management Strategies, Prognostic Considerations

Obesity poses a significant and growing risk factor for chronic kidney disease (CKD), requiring comprehensive evaluation and management strategies. This review explores the intricate relationship between obesity and CKD, emphasizing the diverse phenotypes of obesity, including sarcopenic obesity and metabolically healthy versus unhealthy obesity, and their differential impact on kidney function. We discuss the epidemiological evidence linking elevated body mass index (BMI) with CKD risk while also addressing the paradoxical survival benefits observed in obese CKD patients. Various measures of obesity, such as BMI, waist circumference, and visceral fat assessment, are evaluated in the context of CKD progression and outcomes. Mechanistic insights into how obesity promotes renal dysfunction through lipid metabolism, inflammation, and altered renal hemodynamics are elucidated, underscoring the role of adipokines and the renin-angiotensin-aldosterone system. Furthermore, the review examines current strategies for assessing kidney function in obese individuals, including the strengths and limitations of filtration markers and predictive equations. The management of obesity and associated comorbidities like arterial hypertension, type 2 diabetes mellitus, and non-alcoholic fatty liver disease in CKD patients is discussed. Finally, gaps in the current literature and future research directions aimed at optimizing the management of obesity-related CKD are highlighted, emphasizing the need for personalized therapeutic approaches to mitigate the growing burden of this intertwined epidemic.

Levocarnitine and Dialysis: A Review

Among the various metabolic abnormalities documented in dialysis patients are abnormalities related to the metabolism of fatty acids. Aberrant fatty-acid metabolism has been associated with the promotion of free-radical production, insulin resistance, and cellular apoptosis. These processes have been identified as important contributors to the morbidity experienced by dialysis patients. There is evidence that levocarnitine supplementation can modify the deleterious effects of defective fatty-acid metabolism. Patients receiving hemodialysis and, to a lesser degree, peritoneal dialysis have been shown to be carnitine deficient, as manifested by reduced levels of plasma free carnitine and an increase in the acyl:free carnitine ratio. Cardiac and skeletal muscles are particularly dependent on fatty-acid metabolism for the generation of energy. A number of clinical abnormalities have been correlated with a low plasma carnitine status in dialysis patients. Clinical trials have examined the efficacy of levocarnitine therapy in a number of conditions common in dialysis patients, including skeletal-muscle weakness and fatigue, cardiomyopathy, dialysis-related hypotension, hyperlipidemia, and anemia poorly responsive to recombinant human erythropoietin therapy (rHuEPO). This review examines the evidence for carnitine deficiency in patients requiring dialysis, and documents the results of relevant clinical trials of levocarnitine therapy in this population. Consensus recommendations by expert panels are summarized and contrasted with present guidelines for access to levocarnitine therapy by dialysis patients.

Insulin resistance in chronic kidney disease: a systematic review

Insulin resistance (IR) is an early metabolic alteration in chronic kidney disease (CKD) patients, being apparent when the glomerular filtration rate is still within the normal range and becoming almost universal in those who reach the end stage of kidney failure. The skeletal muscle represents the primary site of IR in CKD, and alterations at sites beyond the insulin receptor are recognized as the main defect underlying IR in this condition. Estimates of IR based on fasting insulin concentration are easier and faster but may not be adequate in patients with CKD because renal insufficiency reduces insulin catabolism. The hyperinsulinemic euglycemic clamp is the gold standard for the assessment of insulin sensitivity because this technique allows a direct measure of skeletal muscle sensitivity to insulin. The etiology of IR in CKD is multifactorial in nature and may be secondary to disturbances that are prominent in renal diseases, including physical inactivity, chronic inflammation, oxidative stress, vitamin D deficiency, metabolic acidosis, anemia, adipokine derangement, and altered gut microbiome. IR contributes to the progression of renal disease by worsening renal hemodynamics by various mechanisms, including activation of the sympathetic nervous system, sodium retention, and downregulation of the natriuretic peptide system. IR has been solidly associated with intermediate mechanisms leading to cardiovascular (CV) disease in CKD including left ventricular hypertrophy, vascular dysfunction, and atherosclerosis. However, it remains unclear whether IR is an independent predictor of mortality and CV complications in CKD. Because IR is a modifiable risk factor and its reduction may lower CV morbidity and mortality, unveiling the molecular mechanisms responsible for the pathogenesis of CKD-related insulin resistance is of importance for the identification of novel therapeutic targets aimed at reducing the high CV risk of this condition.

Obesity and renovascular disease

Obesity remains a prominent public health concern. Obesity not only contributes greatly to cardiovascular events but has also been identified to initiate and affect the progression of preexisting chronic kidney disease. The prevalence of renal artery stenosis is growing world-wide, especially in the elderly population and in individuals with atherosclerotic risk factors such as obesity. Prolonged renovascular disease causes inflammation and microvascular remodeling within the post-stenotic kidney, which promote tissue scarring and may account for irreversible renal damage. Obesity has been shown to aggravate kidney damage via several pathways, including exacerbation of microvascular regression and renal cell injury mediated by adipocytes and insulin resistance, thereby worsening the structural and functional outcomes of the kidney in renovascular disease. Dietary modification and inhibition of the renin-angiotensin-aldosterone system have been shown to alleviate obesity-induced tissue injury and remodeling. Possibly, angiogenic factors may boost microvascular repair in the ischemic kidney in the obesity milieu. Novel therapeutic interventions targeting deleterious pathways that are activated by obesity and responsible for kidney damage need to be explored in future studies.

Insulin resistance in chronic kidney disease: new lessons from experimental models

Insulin resistance (IR) is a common feature of chronic kidney disease (CKD), but the underlying mechanisms still remain unclear. A growing body of evidence suggests that IR and its associated metabolic disorders are important contributors for the cardiovascular burden of these patients. In recent years, the modification of the intestinal flora and activation of inflammation pathways have been implicated in the pathogenesis of IR in obese and diabetic patients. All these pathways ultimately lead to lipid accumulation in ectopic sites and impair insulin signalling. These important discoveries have led to major advances in understanding the mechanisms of uraemia-induced IR. Indeed, recent studies show impairment of the intestinal barrier function and changes in the composition of the gut microbiome during CKD that can contribute to the prevailing inflammation, and the production and absorption of toxins generated from bacterial metabolism. The specific role of individual uraemic toxins in the pathogenesis of IR has been highlighted in rodents. Moreover, correcting some uraemia-associated factors by modulating the intestinal flora improves insulin sensitivity. This review outlines potential mechanisms by which important modifications of body homeostasis induced by the decline in kidney function can affect insulin sensitivity, and the relevance of recent advances in the field to provide novel therapeutic approaches to reduce IR associated cardiovascular mortality.

Protein-bound uremic toxins…new targets to prevent insulin resistance and dysmetabolism in patients with chronic kidney disease

The retention of p-cresyl sulfate (PCS), the prototype of protein-bound uremic toxins that is produced by the gut microbiota and normally excreted by the kidney, may contribute to the development of insulin resistance in patients with chronic kidney disease. In a recent study, we demonstrated in mice, as in cultured muscle cells, that PCS interferes with intracellular insulin signaling pathways and triggers insulin resistance. The treatment of CKD mice with a prebiotic that reduces the intestinal production and decreases blood levels of PCS prevented insulin resistance and lipid abnormalities, suggesting new opportunities to prevent metabolic disturbances in patients with CKD. This study highlights the uremic toxins as new actors in metabolic alterations associated with CKD and allows for the consideration of new therapeutic approaches (e.g., prebiotics, probiotics, adsorbents) to better prevent them.

Postprandial intradialytic dysglycaemia and diabetes in maintenance haemodialysis patients

BACKGROUND

Although the risk of developing dysglycaemia has been investigated in different communities this incidence is poorly studied in patients on maintenance haemodialysis (MHD).

MATERIALS AND METHODS

In a multicentre observational cohort study the occurrence of dysglycaemia was assessed in 239 primary normoglycaemic end stage renal disease (ERSD) patients on MHD. Dysglycaemia (fasting blood glucose > 110 mg dL(-1), > 140 mg dL(-1) 2 h after food intake) or diabetes (fasting blood glucose > 126 mg dL(-1) or > 200 mg dL(-1) at any time) were defined according to WHO criteria and cases were compared with age matched controls within the cohort.

RESULTS

Dysglycaemia was found in 82 primary normoglycaemic ESRD patients (34%) within 31 months after initiation of MHD. In 31 of these patients type 2 diabetes was diagnosed. When compared with matched control MHD patients differences in body mass index (BMI), HbA1c and postprandial blood glucose were detectable (P < 0.05). Increments in 0.1% of HbA1c were related with 11% higher odds for dysglycaemia (P = 0.002). In a subgroup of 36 primary normoglycaemic MHD patients who developed dysglycaemia event-free survival was 64%, 53%, 31%, 17% and 11% after 1, 2, 3, 4 and 5 years of haemodialysis treatment.

CONCLUSION

Onset of dysglycaemia or diabetes is frequent in ESRD patients after onset of chronic haemodialysis. Routine measurement of blood glucose before and after haemodialysis should be implemented as a standard of care during MHD.

Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (calcitriol) and parathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase (LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D receptor was demonstrated by saturation kinetics with radiolabeled calcitriol. Incubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-dependent significant increase in heparin-releasable LPL activity (LPLa) accompanied by a significant increase in LPL mRNA. In contrast, incubation with intact (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose-dependent significant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24-h incubation, 10(-8) M) could be prevented by the calcium channel blocker verapamil. Coincubation with both calcitriol and PTH at equimolar concentration (10(-8) M) resulted in an increase in LPLa and LPL mRNA. These data indicate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alterations in lipoprotein metabolism occurring in uremia.

chiro-inositol deficiency and insulin resistance: a comparison of the chiro-inositol- and the myo-inositol-containing insulin mediators isolated from urine, hemodialysate, and muscle of control and type II diabetic subjects

chiro- and myo-Inositols are major components of the two inositol phosphoglycan mediators of insulin action. Previous work in this laboratory has shown hypo-chiro-inositoluria in type II diabetic subjects and decreased chiro-inositol in mediator prepared from skeletal-muscle biopsies of Pima Indian diabetic subjects together with increased myo-inositol concentrations. Because mediator bioactivity was not previously examined, we decided to isolate the two types of insulin mediator from hemodialysate, urine, and autopsy muscle to investigate their bioactivity in control and type II diabetic subjects. Human mediator fractions were isolated at pH 2.0 and pH 1.3 from hemodialysate, urine, and autopsy muscle of type II diabetic subjects and nondiabetic control subjects. Mediators were assayed for bioactivity, and the relative chiro-inositol/myo-inositol concentration ratio was determined for the mediator pH 2.0 samples by using HPLC or GC/MS. Regardless of source, the chiro-inositol-containing mediator pH 2.0 fractions from type II diabetic subjects were markedly less active than those from controls (50% or less) (P < 0.05). In addition, the chiro-inositol/myo-inositol ratio in samples from type II subjects was significantly reduced (1/3-1/9) compared with controls (P < 0.05 for hemodialysate and P < 0.01 for muscle samples). In contrast, no difference in bioactivity was seen in myo-inositol-containing mediator pH 1.3 samples isolated from the same type II diabetic and control subjects. In type II diabetes there is a generalized deficiency of chiro-inositol mediator in the body in terms of both decreased chiro-inositol mediator (pH 2.0) bioactivity and chiro-inositol content.

Inhibitory effect of methylguanidine on insulin binding to its receptor. Mechanism underlying insulin resistance in uremia

To elucidate the mechanism responsible for the decreased insulin binding to erythrocytes in uremic patients, the effects of incubation with sera obtained from uremic patients or with methylguanidine, respectively, on insulin binding were examined. Insulin binding to erythrocytes from uremic patients was lower than that from normal subjects (3.1 +/- 0.19% vs 6.6 +/- 0.33%, Mean +/- SEM, P less than .005), being due mainly to decreased binding affinity (58% of control). Incubation of erythrocytes with 1:5 diluted sera of uremic patients resulted in decreased insulin binding (65 +/- 5% of control) and this decrease was restored to the level of 78 +/- 3% of the controls after incubation with buffer for 12 h. Methylguanidine inhibited insulin binding to erythrocytes in a dose-dependent manner. Post-dialyzed serum with 100 ng/ml of methylguanidine (as seen in pre-dialyzed uremic patients) inhibited insulin binding to erythrocytes as much as pre-dialyzed serum (54.3 +/- 3% vs 47 +/- 1% of control). Incubation of IM-9 lymphocytes with 100 ng/ml of methylguanidine did not alter the insulin receptor mRNA level. These results suggest that methylguanidine inhibits insulin binding to its receptor, resulting in decreased insulin binding to erythrocytes.

Muscle insulin resistance in uremic humans: glucose transport, glucose transporters, and insulin receptors

To determine the cellular basis for insulin resistance observed in patients with uremia, we investigated insulin action in vivo and in vitro using skeletal muscle obtained from patients with chronic renal failure. Uremic subjects had significantly reduced rates of insulin-stimulated glucose disposal, as determined by a 3-h intravenous glucose tolerance test and using the hyperinsulinemic euglycemic clamp technique. Hepatic glucose production was similar before (control, 76.2 +/- 6.3 vs. uremic, 74.2 +/- 6.9 mg.kg-1.min-1) and during insulin infusion at 40 mU.m-2.min-1 (control, -60.9 +/- 6.6 vs. uremic, -53.9 +/- 6.3 mg.kg-1.min-1). In incubated human skeletal muscle fiber strips, basal 2-deoxy-D-glucose transport was unchanged in uremic subjects compared with controls. However, the increase in insulin-stimulated glucose transport was significantly reduced by 50% in muscles from uremic patients (P = 0.012). In partially purified insulin receptors prepared from skeletal muscle, 125I-labeled insulin binding, beta-subunit receptor autophosphorylation, and tyrosine kinase activity were all unchanged in uremic subjects. The abundance of insulin-sensitive (muscle/fat, GLUT-4) glucose transporter protein measured by Western blot using Mab 1F8 or polyclonal antisera was similar in muscles of control and uremic patients. These findings suggest that the insulin resistance observed in skeletal muscle of uremic patients cannot be attributed to defects in insulin receptor function or depletion of the GLUT-4 glucose transporter protein. An alternative step in insulin-dependent activation of the glucose transport process may be involved.

Alterations of glucose transporter systems in insulin-resistant uremic rats

To further define the cellular alteration(s) involved in the impaired glucose transport associated with chronic uremia, we examined the concentration and translocation of glucose transport systems in adipocytes isolated from partially nephrectomized uremic rats. Uremic animals, compared with matched controls, had increased blood urea nitrogen and serum insulin, whereas serum glucose was unchanged. In agreement with previous work, 125I-insulin binding to its receptor was unaltered and transport of 2-deoxy-D-glucose was decreased in both the absence (basal) and presence of a maximal (7 nM) insulin concentration by 44 and 35%, respectively. To assess the movement and concentration of glucose transport systems in various membrane fractions prepared from basal and insulin-treated (20 nM) uremic fat cells, the technique of D-glucose-inhibitable cytochalasin B binding was utilized. In plasma membranes isolated from these cells the concentration of glucose transporters was decreased by 16 (P less than 0.01) and 30% (P less than 0.005) in basal and insulin-treated cells, respectively. Concomitantly, microsomal membranes prepared from uremic cells treated in the absence and presence of insulin had a 28 (P less than 0.01) and 15% (P less than 0.05) decrease in concentration of glucose transport systems, respectively. Additionally, glucose transporter concentration was significantly decreased by 17% (P less than 0.025) in total membranes prepared from uremic cells. Thus, impairment of glucose transport in uremic fat cells can be attributed to a postbinding defect that, at least in part, results from a decrease in the total concentration of glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

Review: mechanisms for abnormal protein metabolism in uremia

Loss of protein stores, reflected by negative nitrogen balance and accelerated accumulation if nitrogenous breakdown products, is an important factor in the morbidity of chronic renal failure and the high mortality rate of acute renal failure. Low protein intake intensifies the suppressed protein synthesis that results from impaired insulin-stimulated protein anabolism. The metabolic acidosis of uremia contributes to tissue loss, both by increasing muscle protein degradation, and by raising the requirements for essential amino acids. Correcting metabolic acidosis improves the nitrogen balance and reduces tissue wasting. It is important to ensure adequate nutrient intakes, rather than the low protein diet often prescribed to slow loss of renal function.

Neutrophil activation during hemodialysis

Oxidative metabolism of PMNs of uremic patients is enhanced due to unknown serum (plasma) factors which are removed during hemodialysis. Respiratory burst activity is diminished in both PMA-stimulated and unstimulated states compared to healthy controls. Hemodialysis normalizes stimulated and decreases unstimulated hydrogen peroxide production. Several authors found that resting and stimulated chemiluminescence (CL) during hemodialysis correlates with complement activation, whereas other authors describe CL using dialyzer membranes with only mild anaphylatoxin formation. Alterations of PMN carbohydrate metabolism in uremic patients improves during HD with polysulfone. HD with PMMA, however, activates glycogenolysis. These alterations may be responsible for disturbance in phagocytosis. Degranulation during HD also occurs in absence of complement activation. Calcium channel blockers decrease activation of PMNs using dialyzers with only little anaphylatoxin formation.

Abnormal cation transport in uremia. Mechanisms in adipocytes and skeletal muscle from uremic rats

The cause of the abnormal active cation transport in erythrocytes of some uremic patients is unknown. In isolated adipocytes and skeletal muscle from chronically uremic chronic renal failure rats, basal sodium pump activity was decreased by 36 and 30%, and intracellular sodium was increased by 90 and 50%, respectively, compared with pair-fed control rats; insulin-stimulated sodium pump activity was preserved in both tissues. Lower basal NaK-ATPase activity in adipocytes was due to a proportionate decline in [3H]ouabain binding, while in muscle, [3H]ouabain binding was not changed, indicating that the NaK-ATPase turnover rate was decreased. Normal muscle, but not normal adipocytes, acquired defective Na pump activity when incubated in uremic sera. Thus, the mechanism for defective active cation transport in CRF is multifactorial and tissue specific. Sodium-dependent amino acid transport in adipocytes closely paralleled diminished Na pump activity (r = 0.91), indicating the importance of this defect to abnormal cellular metabolism in uremia.

Insulin resistance in uremia: in vitro model in the rat liver using human serum to study mechanisms

We have previously demonstrated in a rat model of chronic uremia that the liver is resistant to insulin. To further investigate the mechanism(s) of insulin resistance in uremia, primary cultures of normal rat hepatocytes were incubated with varying dilutions (1/10 to 1/10,000) of sera from undialyzed end stage uremic and normal humans for 20 hours. We then studied insulin action, binding, and postbinding events. Dilutions of uremic sera as low as 1/1,000 rendered the hepatocytes resistant to maximal concentrations of insulin with regard to [14C]acetate incorporation into lipids. The dose response curve for insulin-stimulated [14C]aminoisobutyric acid uptake demonstrated a shift to the right in hepatocytes incubated with uremic sera when compared with those incubated with normal sera. The 125I-insulin binding sites and affinity, 125I-insulin internalization and degradation, insulin receptor structure, autophosphorylation of the insulin receptor, and its tyrosine-specific kinase activity were normal in the hepatocytes rendered resistant to insulin by uremic sera. However, these cells failed to generate the chemical mediator or second messenger of insulin action, as assessed by its ability to stimulate pyruvate dehydrogenase (PDH) in liver mitochondria from normal rats. We concluded that uremic sera renders normal rat hepatocytes resistant to insulin. Insulin resistance is a postinsulin receptor kinase defect possibly due to lack of the generation of the chemical mediator of insulin action. This in vitro cell model may be useful to further define the mechanism(s) and the serum factor(s) responsible for insulin resistance in uremia in the absence of complicating hormonal and substrate changes that occur in vivo.

Protein synthesis and degradation in skeletal muscle of chronically uremic rats

We used the perfused hemicorpus preparation to measure individual rates of protein synthesis and degradation. Using fed animals, perfused either with or without insulin, muscle protein synthesis and hemicorpus protein degradation rates were similar, but myofibrillar protein degradation was clearly increased in the uremic preparations. When the animals were fasted, differences in the rates of skeletal muscle protein turnover were apparent. Uremic rats lost more wt at both 24 and 48 hr of fasting when compared to either ad libitum fed or pair-fed controls who started fasting at body wts equivalent to our uremic rats. The accelerated wt loss was accompanied by lower rates of protein synthesis, higher degradation rates, and greater net protein catabolism in our uremic rats. Alterations in body lipid content were present in uremia and correlated with the rate of protein degradation in both control and uremic rats. These data demonstrated that even in the fed state, uremia is associated with subtle alterations in skeletal muscle protein turnover. When stressed, these alterations become more pronounced. Insufficient stores of body lipids, either due to inadequate nutrition or altered metabolism, may contribute to the alterations in muscle protein turnover seen in chronic renal insufficiency.

Postbinding defects of insulin action in human adipocytes from uremic patients

It is now well established that longstanding human uremia is associated with impaired in vivo insulin action on glucose utilization of peripheral target tissues. In an attempt to define the cellular basis of the uremic insulin resistance we studied insulin action in adipocytes from eight patients with undialyzed chronic uremia and from eight matched healthy controls. (125I)-Insulin binding to fat cells from uremic patients was normal. In contrast (14C)-D-glucose transport exhibited decreased sensitivity to insulin. The concentrations of insulin that elicited half-maximal response was 422 +/- 95 pmoles/liter in uremic patients and 179 +/- 38 pmoles/liter in normal subjects (P less than 0.01). The noninsulin- and the maximal insulin-stimulated glucose transport of adipocytes from uremic patients with normal. (14C)-D-glucose conversion to total lipids was also measured in these cells in the absence and presence of various insulin concentrations. Similar to the findings in transport studies the lipogenesis of fat cells from uremic patients had depressed sensitivity to insulin (half-maximal stimulation at 38 +/- 8 pmoles/liter in uremic patients and at 11 +/- 3 pmoles/liter in normal subjects, P less than 0.01) with unchanged noninsulin and maximal insulin-stimulated lipogenesis. Taken together these results suggest that the insulin resistance of adipocytes from patients with chronic uremia may be accounted for primarily by postbinding defects localized to glucose transport and metabolism.

Muscle protein turnover: effects of exercise training and renal insufficiency

Chronic renal failure is associated with an enhanced catabolism of muscle protein. To determine the effect of exercise training and moderate renal insufficiency on net protein catabolism and protein synthesis in isolated epitrochlearis muscles, three-fourth nephrectomized and control rats were exercise trained or remained sedentary. Net muscle protein degradation was determined by measuring the rates of release of phenylalanine and tyrosine. Protein synthesis was determined by measuring the incorporation of [U-14C]phenylalanine into muscle protein. Exercise training reduced the elevated protein degradation of uremia to control levels. In control rats, exercise training had no effect on protein degradation. Exercise training increased alanine release in control rats but did not further increase the elevated alanine release of uremia. Protein synthesis was unaffected by both uremia and exercise training. Exercise training in control and uremic rats moderately increased the responsiveness of muscle to insulin by reducing net protein degradation but did not further enhance the insulin-stimulated increase in protein synthesis. Thus exercise training ameliorates the enhanced muscle protein degradation of moderate renal insufficiency.

Characterization and partial purification of a factor from uremic human serum that induces insulin resistance

We have previously shown that the incubation of normal rat adipose tissue with sera from nondialyzed, nondiabetic uremic patients reduces the transport and metabolism of glucose, in the absence and presence of insulin. In this study insulin-stimulated glucose metabolism by normal rat adipocytes was used as a bioassay to identify the resistance activity, assess the effect of chemical modification on it, and the clinical states associated with its production. The resistance activity was trypsin-labile and had an apparent isoelectric point between 6 and 7, but was not retained by either protein A or concanavalin A columns. The insulin resistance activity was decreased by coincubation with the protein synthesis inhibitor, cycloheximide. Purification to greater than 200,000-fold was attained by heating (100 degrees C) uremic serum, subjecting the supernatant to Sephadex G-25 chromatography and subsequent adsorption to DEAE at pH 7.8 and elution at pH 6.5. The partially purified resistance activity was retained within dialysis tubing of 1,000-mol wt cutoff but not within 2,000-mol wt cutoff. Hemodialysis of patients over 1 wk to 18 mo reduced significantly the amount of resistance activity in their sera. The resistance activity, present in most uremic patients, was not found in the sera of individuals with normal renal function but who were either obese, fasted, elderly or had type II diabetes mellitus. Thus, a circulating small molecular weight peptide, unique to uremia, induced insulin resistance by a protein synthesis-dependent mechanism.