Early fasting glucose measurements can predict later glycaemic response to once weekly dulaglutide.

AIMS: To assess whether early measures of fasting blood glucose predict later glycaemic response with once-weekly dulaglutide in patients with Type 2 diabetes mellitus. METHODS: Post hoc analyses were conducted separately for two phase 3 studies (AWARD-5 and AWARD-1) in patients assigned to once-weekly dulaglutide. Week 2 fasting blood glucose was used as a predictor variable, and glycaemic treatment response was defined by HbA1c response based on a composite efficacy endpoint. The association between fasting blood glucose and the glycaemic response was analysed using chi-square tests. RESULTS: There was a strong association between fasting blood glucose < 7.9 mmol/l at week 2 and achieving the HbA1c composite efficacy endpoint at week 26 (P < 0.01). Higher fasting blood glucose at week 2, however, did not predict absence of glycaemic response and requires further assessment. CONCLUSIONS: Fasting blood glucose measured at 2 weeks may be an early and useful predictor of glycaemic response to once-weekly dulaglutide treatment.

A randomized clinical trial of basal insulin peglispro vs NPH in insulin-naïve patients with type 2 diabetes: the IMAGINE 6 trial.

AIMS: Basal insulin peglispro (BIL) has a longer duration of action than conventional insulin analogues and a hepato-preferential mechanism of action. This study assessed whether BIL was non-inferior to isophane insulin (NPH) in reducing HbA1c in insulin-naïve patients with type 2 diabetes, when added to pre-study oral anti-hyperglycaemic medications. MATERIALS AND METHODS: This was a Phase 3, open-label, treat-to-target (TTT), randomized trial with a 2-week lead-in, 26-week treatment and a 4-week safety follow-up period. Patients were randomized to bedtime (pm) NPH, morning (am) BIL or pm BIL in a 1:1:1 ratio. RESULTS: Six hundred and forty-one patients [NPH, n = 213; BIL, n = 428 (am, n = 213; pm, n = 215)] received study drug. BIL was non-inferior to NPH for HbA1c change from baseline at Week 26 with a between-treatment difference (95% confidence interval) of -0.37% (-0.50, -0.23%). HbA1c at baseline was 8.5%, and was lower in BIL- vs NPH-treated patients after 26 weeks of treatment (6.8% vs 7.1%; P < .001). More BIL-treated patients achieved HbA1c <7.0% and HbA1c <7.0% without nocturnal hypoglycaemia. Fasting serum glucose levels and nocturnal hypoglycaemia rates were lower in BIL-treated patients; total hypoglycaemia rates were similar. Treatment-emergent adverse events were similar between groups. Fasting triglycerides decreased from baseline in both groups and to a greater extent with NPH, but were not significantly different between groups at Week 26. Mean alanine aminotransferase (ALT) increased with BIL treatment, but there was no evidence of acute severe hepatotoxicity. CONCLUSIONS: In this TTT study, BIL treatment showed clinically relevant improvements in glycaemic control and a significant reduction in nocturnal hypoglycaemia compared to NPH.

The need for better insulin therapy.

Insulin replacement therapy corrects a core defect of diabetes pathophysiology. Since its introduction as a therapeutic modality almost 100 years ago, insulin therapy has undergone remarkable changes in purity and ability to provide more physiologic control of blood glucose levels. With glucose-lowering potential limited only by risks of hypoglycaemia, which remains the major limitation in our ability to achieve glycaemic goals, insulin replacement therapy remains a cornerstone of therapy. Major progress in reducing the risks of hypoglycemia has occurred with the development of insulin analogs. This review article briefly chronicles the evolution of insulin replacement strategies, highlighting both challenges in pharmaceutical development and patient acceptance, underscoring achievements, as well as denoting what improvements are still needed.

Monotherapy with the once-weekly GLP-1 analogue dulaglutide for 12 weeks in patients with Type 2 diabetes: dose-dependent effects on glycaemic control in a randomized, double-blind, placebo-controlled study.

AIMS: Evaluate dose-dependent effects of once-weekly dulaglutide, a glucagon-like peptide-1 analogue, on glycaemic control in patients with Type 2 diabetes treated with lifestyle measures with or without previous metformin. METHODS: This 12-week, double-blind, placebo-controlled, dose-response trial randomized 167 patients who were anti-hyperglycaemic medication-naïve or had discontinued metformin monotherapy [mean baseline HbA(1c) 59 ± 8 to 61 ± 8 mmol/mol (7.6 ± 0.7 to 7.8 ± 0.8%)] to once-weekly injections of placebo or dulaglutide (0.1, 0.5, 1.0 or 1.5 mg). RESULTS: A significant dose-dependent reduction in HbA(1c) (least squares mean ± SE) was observed across doses (P < 0.001). HbA(1c) reductions in the 0.5, 1.0 and 1.5 mg dulaglutide groups were greater than in the placebo group [-10 ± 1, -11 ± 1 and -11 ± 1 vs. 0 ± 1 mmol/mol (-0.9 ± 0.1, -1.0 ± 0.1 and -1.0 ± 0.1 vs. 0.0 ± 0.1%), respectively, all P < 0.001]. Dose-dependent reductions in fasting plasma glucose were also observed [least squares mean difference (95% CI) ranging from -0.43 (-1.06 to 0.19) mmol/l for dulaglutide 0.1 mg to -1.87 (-2.56 to -1.19) mmol/l for dulaglutide 1.5 mg, P < 0.001]. Dose-dependent weight loss was demonstrated across doses (P = 0.009), but none of the groups were different from placebo. The most common adverse events were nausea and diarrhoea. CONCLUSIONS: The observed dulaglutide dose-dependent reduction in HbA(1c) and its acceptable safety profile support further clinical development for treatment of Type 2 diabetes.

Defect in phosphorylation of insulin receptors in cells from an insulin-resistant patient with normal insulin binding.

Mononuclear blood cells were obtained from a patient with type A insulin resistance. The cells showed a normal ability to bind iodine 125-labeled insulin. Analysis of solubilized insulin receptors from the patient's cells revealed a defect in insulin-stimulated tyrosine kinase activity, which is closely associated with the receptor itself. The enzyme failed to phosphorylate the insulin receptor and showed a markedly reduced ability to phosphorylate exogenously added substrates. It appears that receptors from this insulin-resistant patient have a defect distal to the insulin-binding site (the alpha subunit of the receptor). The defect could be located in the beta subunit, which has an adenosine triphosphate-binding site, or in another receptor component that transfers a signal of insulin binding into kinase activity. This dissociation between the normal binding and the defective protein kinase component of the insulin receptor represents the first biochemical defect of the receptor distal to ligand binding.

Relationship of insulin binding and insulin-stimulated tyrosine kinase activity is altered in type II diabetes.

The insulin receptor contains an alpha subunit with insulin binding properties and a beta subunit with insulin-stimulated tyrosine kinase function. Preparations containing insulin and insulinlike growth factor I (IGF-I) receptors were obtained from solubilized human red cell membranes by affinity chromatography. After separate assays for insulin binding and insulin-stimulated tyrosine kinase activities, a high degree of correlation was found between these activities in preparations from normals and diabetics. Identical studies using IGF-I as the ligand showed a lesser degree of correlation. We compared 24 normal subjects and 14 untreated type II diabetics and found significant diminution in the slope of the line coupling insulin binding and insulin-stimulated kinase activities in the diabetics. This difference was not observed in a similar study of IGF-I-related activities. Compared to normal controls, untreated type II diabetics have reduced tyrosine kinase activity stimulated per unit insulin binding.

Insulin receptor of human cerebral gliomas. Structure and function.

The insulin receptor from human brain tumors of glial origin was examined for the first time using intact cells (from an established cultured human glioblastoma cell line) and partially purified solubilized membranes (from cultured cells and freshly isolated human brain tumors). The structure of the glial insulin receptor subunits was assessed by affinity cross-linking of 125I-insulin with the alpha-subunit of the receptor, neuraminidase treatment of the cross-linked receptor, behavior of the receptor on lectin columns, and electrophoretic mobility of the phosphorylated beta-subunit. The functions of the insulin receptor were examined by measuring specific 125I-insulin binding (receptor concentration, affinity, specificity, pH-, time-, and temperature dependence), insulin-induced down-regulation of the receptor, insulin-stimulated autophosphorylation of the beta-subunit, and phosphorylation of exogenous substrates as well as insulin-stimulated glucose uptake in glioblastoma cells. All of these properties were typical for the insulin receptor from target tissues for insulin action. The insulin receptor of the normal human brain showed the altered electrophoretic mobility and lack of neuraminidase sensitivity of its alpha-subunit previously reported for the rat brain receptor. There was no difference, however, in the functions of the receptor subunits (binding, phosphorylation) from the normal brain tissue and the eight human gliomal tumors. Since the glial elements compose a majority of the brain cells, the "normal" structure and function of their insulin receptor might provide a key to understanding the role of insulin in the carbohydrate metabolism of the human central nervous system.

Effects of autonomic neuropathy on coronary blood flow in patients with diabetes mellitus.

BACKGROUND: C ardiac sympathetic signals play an important role in the regulation of myocardial perfusion. We hypothesized that sympathetically mediated myocardial blood flow would be impaired in diabetics with autonomic neuropathy. METHODS AND RESULTS: We studied 28 diabetics (43+/-7 years old) and 11 age-matched healthy volunteers. PET was used to delineate cardiac sympathetic innervation with [(11)C]hydroxyephedrine ([(11)C]HED) and to measure myocardial blood flow at rest, during hyperemia, and in response to sympathetic stimulation by cold pressor testing. The response to cardiac autonomic reflex tests was also evaluated. Using ultrasonography, we also measured brachial artery reactivity during reactive hyperemia (endothelium-dependent dilation) and after sublingual nitroglycerin (endothelium-independent dilation). Based on [(11)C]HED PET, 13 of 28 diabetics had sympathetic-nerve dysfunction (SND). Basal flow was regionally homogeneous and similar in the diabetic and normal subjects. During hyperemia, the increase in flow was greater in the normal subjects (284+/-88%) than in the diabetics with SND (187+/-80%, P=0.084) and without SND (177+/-72%, P=0.028). However, the increase in flow in response to cold was lower in the diabetics with SND (14+/-10%) than in those without SND (31+/-12%) (P=0.015) and the normal subjects (48+/-24%) (P<0.001). The flow response to cold was related to the myocardial uptake of [(11)C]HED (P<0.001). Flow-mediated brachial artery dilation was impaired in the diabetics compared with the normal subjects, but it was similar in the diabetics with and without SND. CONCLUSIONS: Diabetic autonomic neuropathy is associated with an impaired vasodilator response of coronary resistance vessels to increased sympathetic stimulation, which is related to the degree of SND.

An alteration in apparent molecular weight of the insulin receptor from the human monocyte cell line U-937.

We have studied the structure of the insulin receptor from a human cultured monocyte cell line, U-937. The receptor is composed of alpha and beta subunits as seen in other insulin receptors, but these subunits are of greater apparent molecular weight (alpha 150,000 and beta 102,000) than in typical insulin receptors. Despite this, the U-937 insulin receptor appears to function normally. The alpha subunit binds insulin and the beta subunit is phosphorylated in response to insulin stimulation. Both subunits are expressed in the plasma membrane. Insulin binding isotherms are similar to those seen in IM-9 lymphocytes. Thus, the insulin receptor from U-937 monocytes appears functionally normal despite alterations in molecular weight of the subunits.

Sulfonylureas do not affect insulin binding or glycemic control in insulin-dependent diabetics.

Sulfonylureas alone are ineffective in the therapy of insulin-independent diabetes mellitus (IDDM). These agents, however, might serve as an adjunct to insulin treatment if they directly affect insulin binding to its receptor. We studied 11 patients with IDDM to determine whether chlorpropamide acts directly on the insulin receptor and whether it could augment the effect of insulin on glycemic control. Mean tracer insulin binding to both peripheral monocytes and erythrocytes in 11 poorly controlled patients was normal. Optimization of glucose control by continuous subcutaneous insulin infusion for 7--10 days did not alter insulin binding to either cell type. Addition of chlorpropamide, 250--500 mg/day for another 7--10 days did not affect any aspect of insulin binding (tracer binding, number of receptor sites, insulin sensitivity, or affinity) in either cell type. Insulin binding was not changed in one patient after 3 days of 250 mg/day of the drug and in another after 500 mg/day over 3 mo. The sulfonylurea, in addition, provides no additive effect with insulin on blood glucose levels or insulin doses required to maintain euglycemia. We conclude that short-term use of chlorpropamide in addition to insulin in IDDM does not alter insulin binding to circulating monocytes or erythrocytes. In addition, we were unable to show that this agent is a clinically useful adjunct to insulin in IDDM.

Diacylglycerol modulation of insulin receptor from cultured human mononuclear cells. Effects on binding and internalization.

Tumor-promoting phorbol esters alter binding of growth factors and hormones to their specific receptors. Action of diacylglycerols, endogenous phorbol ester analogues, on 125I-labeled insulin binding to its receptor from human cells was therefore investigated. A variety of 1,2-diacylglycerols and 1,3-diacylglycerols inhibited 125I-insulin binding to intact human monocyte-like (U-937) and lymphoblastoid (IM-9) cells in a dose-, time-, and temperature-dependent manner within 30 sec at 37 degrees C in a fashion analogous to that of the tumor-promoting phorbol diester 12-O-tetradecanoylphorbol-13-acetate (TPA). Inhibition of insulin binding by diacylglycerols, analyzed by Scatchard plot, seems to be due to altered binding affinity of the insulin receptor. Diacylglycerol effects were reversible, were seen regardless of the order of addition of 125I-insulin and diacylglycerols, and were demonstrated only with occupied insulin receptors. Corresponding fatty acids or phospholipids did not affect specific insulin binding to the intact U-937 cells. Diacylglycerols also inhibited binding of 125I-insulin-like growth factor (IGF) I but not that of 125I-human growth hormone (HGH) to the human cells. The non-tumor-promoting phorbols (phorbol, 4-alpha-phorbol, phorbol-12,13-distearate) did not affect insulin binding to intact cells. Both diacylglycerols and TPA stimulated internalization of 125I-insulin by U-937 and IM-9 cells. The ability of diacylglycerol to mimic the effects of TPA on the insulin receptor supports the concept of diacylglycerols as endogenous phorbol diester analogues even though the sole role of protein kinase C in our system is doubtful.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of the insulin receptor tyrosine kinase.

Insulin is a polypeptide hormone consisting of 51 amino acids. Insulin promotes a variety of anabolic enzymatic pathways and inhibits many catabolic enzymatic pathways involved in energy storage, as well as in synthesis of structural tissue proteins. In addition, insulin serves as a growth factor, modulating mitogenesis, growth and differentiation. Insulin mediates all of its effects by initially binding and activating its specific cell-surface receptor. Conformational changes induced by insulin binding lead to activation of intrinsic receptor tyrosine kinase. Thus, the study of tyrosine kinase inhibitors, whether synthetically produced or purified from microorganisms or humans, has led to elucidation of molecular details of physiological insulin signaling.

Recombinant human alpha 2-HS glycoprotein inhibits insulin-stimulated mitogenic pathway without affecting metabolic signalling in Chinese hamster ovary cells overexpressing the human insulin receptor.

Insulin acts on its target tissues by specific interaction with the cell surface insulin receptor (IR). The IR possesses an intrinsic tyrosine kinase (TK) activity which is stimulated by insulin binding. This TK activity is required for many aspects of insulin signalling. We had earlier reported that human plasma alpha 2-HS glycoprotein (alpha 2-HSG) inhibits insulin-stimulated mitogenesis at the level of IR-TK (Mol Endo 7: 1445-1455, 1993). In the present study, using recombinant alpha 2-HSG, which possesses 50-100 times the specific activity of plasma alpha 2-HSG, we have further investigated the molecular basis of this effect. We examined the insulin-stimulated Ras signalling pathway in Chinese Hamster Ovary cells overexpressing the human IR. alpha 2-HSG inhibits insulin-induced tyrosine phosphorylation of IRS-1 and the subsequent association of GRB2, as well as Sos, with IRS-1. This inhibition results in reduced guanine nucleotide exchange in p21ras. alpha 2-HSG also inhibits the stimulation of Raf phosphorylation, in response to insulin, leading to inhibition of MEK activity. In a parallel pathway, alpha 2-HSG also inhibits insulin-induced tyrosine phosphorylation of Shc. However, alpha 2-HSG does not affect any of the metabolic actions of insulin rested in these cells. These results suggest that, while insulin's mitogenic effects can be abolished by inhibition of insulin-induced IR-TK, propagation of signals for metabolic activities might utilize alternate of rescue mechanisms.

Serum alpha 2-HS-glycoprotein is an inhibitor of the human insulin receptor at the tyrosine kinase level.

The insulin-dependent tyrosine kinase activity (TKA) of the insulin receptor (IR) plays an essential role in insulin signaling. Thus, dysregulation of IR-TKA might be an important element in the states of insulin resistance. A phosphorylated rat hepatic glycoprotein (pp63) acting as an inhibitor of IR-TK has been described. In search of the human homolog of pp63, we isolated a cDNA clone from a human liver lambda gt11 cDNA library. DNA sequence analysis reveals identity with the mRNA product of a human gene AHSG encoding a serum protein, alpha 2-Heremans Scmid-glycoprotein (alpha 2HSG), with heretofore unknown physiological function. Northern blot analysis demonstrates a 1.8-kilobase mRNA in human liver and HepG2 hepatoma cells. alpha 2HSG, purified from human serum, specifically inhibits insulin-stimulated IR autophosphorylation in vitro and in vivo as well as exogenous substrate tyrosine phosphorylation. alpha 2HSG also inhibits both insulin-induced tyrosine phosphorylation of IRS-1 and the association of IRS-1 with the p85 subunit of phosphatidylinositol-3 kinase in H-35 hepatoma cells. alpha 2HSG inhibits insulin-dependent mitogenesis, but does not affect insulin-stimulated induction of the metabolic enzyme tyrosine aminotransferase. alpha 2HSG does not compete with insulin for binding to IR. Finally, the action of alpha 2HSG is specific toward the IR-TK; its effect does not extend to insulin-like growth factor-I-stimulated TKA. Our results allow us to assign a biochemical function for human alpha 2HSG, namely regulation of insulin action at the IR-TK level.

Maintenance of sulfonylurea responsiveness in NIDDM. Randomized double-blind study of intermittent glyburide therapy.

OBJECTIVE: To assess the effectiveness of intermittent administration of sulfonylurea (glyburide) to patients with non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: A randomized, double-blind, prospective trial compared daily administration with intermittent administration of glyburide to patients who initially responded to the drug. Twenty-eight of 60 patients with NIDDM achieved the predetermined improvement in plasma glucose concentration on glyburide therapy. These 28 responders were enrolled into a 16-wk trial of daily versus intermittent (2 wk on, 2 wk off) glyburide treatment. Laboratory assessment of glycemic control and insulin secretion in fasting and 2-h postprandial states was done every 2 wk. RESULTS: Patients on continuous glyburide therapy maintained their glycemic control throughout the study. In contrast, patients on the intermittent schedule lost their glycemic control immediately after being placed on placebo. Despite a significant response to each sulfonylurea pulse, these subjects never regained their baseline glycemic levels. Their fructosamine and HbA1c concentrations deteriorated and remained significantly higher than those of the continuously treated subjects. CONCLUSIONS: Results suggest that administration of glyburide on an intermittent basis after a 2-wk drug-free period to patients initially rendered responsive to sulfonylurea therapy is without clinical merit.

The safety of injecting insulin through clothing.

OBJECTIVE: Many of the "antiseptic" practices recommended by health care professionals for insulin injection have been successfully challenged as unnecessary. Since people with diabetes have long been observed to inject their insulin through their clothing, this study was undertaken to determine the safety and perceived benefits of administering insulin by this "rogue" technique. RESEARCH DESIGN AND METHODS: Fifty people with insulin-treated diabetes were randomized into a 20-week single-blinded prospective crossover study comparing the conventional subcutaneous injection technique (with skin preparation) to an experimental injection technique through clothing. Skin assessment, glycated hemoglobin levels, and leukocyte count were determined before randomization, at 10 weeks (before crossover), and again at 20 weeks (at completion). The participants injected through a single layer of fabric, which ranged from nylon to denim. Problems, benefits, type of clothing, and other comments were recorded by the subjects in an injection log. RESULTS: Forty-two (84%) subjects completed the study. The mean age was 41 years (range, 23-63 years), 50% were women, 86% were Caucasian, and 80% had type I diabetes. The mean duration of diabetes was 14 years (range, 1-33 years). Fifty-one percent had > 16 years of education. The demographic characteristics of the dropouts were similar to those who completed the study. Over the 20-week period approximately 13,720 injections were performed by participants. None of the subjects experienced erythema, induration, or abscess at injection sites. Neither the glycated hemoglobin levels nor the leukocyte counts differed between the conventional and experimental regimens. During the injection-through-clothing phase of the study, only minor problems, such as blood stains on clothing and bruising, were recorded in the logbooks. However, subjects reported that injection through clothing offered benefits such as convenience and saving time. CONCLUSIONS: It is safe and convenient to inject insulin through clothing.

Once- and twice-daily dosing with rosiglitazone improves glycemic control in patients with type 2 diabetes.

OBJECTIVE: To determine the efficacy of rosiglitazone compared with placebo in reducing hyperglycemia. RESEARCH DESIGN AND METHODS: After a 4-week placebo run-in period, 959 patients were randomized to placebo or rosiglitazone (total daily dose 4 or 8 mg) for 26 weeks. The primary measure of efficacy was change in the HbA1c concentration. RESULTS: Rosiglitazone produced dosage-dependent reductions in HbA1c of 0.8, 0.9, 1.1, and 1.5% in the 4 mg o.d., 2 mg b.i.d., 8 mg o.d., and 4 mg b.i.d. groups, respectively, compared with placebo. Clinically significant decreases from baseline in HbA1c were observed in drug-naive patients at all rosiglitazone doses and in patients previously treated with oral monotherapy at rosiglitazone 8 mg o.d. and 4 mg b.i.d. Clinically significant decreases from baseline in HbA1c were also observed with rosiglitazone 4 mg b.i.d. in patients previously treated with combination oral therapy. Approximately 33% of drug-naive patients treated with rosiglitazone achieved HbA1c < or =7% at study end. The proportions of patients with at least one adverse event were comparable among the rosiglitazone and placebo groups. There was no evidence of hepatotoxicity in any treatment group. There were statistically significant increases in weight and serum lipids in all rosiglitazone treatment groups compared with placebo. For LDL and HDL cholesterol, the observed increase appeared to be dose related. CONCLUSIONS: Rosiglitazone at total daily doses of 4 and 8 mg significantly improved glycemic control in patients with type 2 diabetes and was well tolerated.

The influence of treatment modality and ethnicity on attitudes in type 2 diabetes.

OBJECTIVE: The study examines diabetes attitude differences by treatment modality (insulin vs. no insulin), race/ethnicity, and the interaction of these two variables for people with type 2 diabetes. RESEARCH DESIGN AND METHODS: Data were collected with the Diabetes Care Profile (DCP), an instrument that assesses psychosocial factors related to diabetes. Participants (n = 672) were recruited in the metropolitan Detroit, Michigan, area from 1993 to 1996. A total of 68% of these participants were African-Americans with type 2 diabetes, and 32% were Caucasians with type 2 diabetes. Analyses of covariance were performed to examine the effects of race/ethnicity, treatment, and their interaction for each DCP scale. RESULTS: The four patient categories (two ethnicities by two treatment modalities) differed by age, years with diabetes, education, and sex distribution. Treatment modality had a significant effect on 6 of the 16 DCP scales (Control, Social and Personal Factors, Positive Attitude, Negative Attitude, Self-Care Ability, and Exercise Barriers). Ethnicity was a significant effect for three scales (Control, Support, and Support Attitudes). The interaction of race/ethnicity and treatment modality was a significant effect for two related attitude scales (Positive Attitude and Negative Attitude). CONCLUSIONS: The results suggest that attitudes toward diabetes are similar for African-American and Caucasian patients with type 2 diabetes. The results also suggest that treatment modality has a greater effect on attitudes than either race/ethnicity or the interaction effect. However, Caucasian patients using insulin differed from the other patient groups by having the least positive and the most negative attitudes regarding diabetes.

Insulin antagonistic effects of insulin receptor antibodies on plasma membrane (Ca2+ + Mg2+) ATPase activity: a possible etiology of type B insulin resistance.

The regulatory effect of insulin on plasma membrane (Ca2+ + Mg2+)ATPase activity in target tissues for insulin was proposed to be of importance in mediating the hormone's cellular action. Consequently, polyclonal insulin receptor antibodies from patients with type B insulin resistance (B7 and B10) were used as probes to further explore a possible role for this ATPase in insulin action. The antibodies B7 and B10 obtained during the active phase of the disease manifested insulinomimetic actions in rat renal cortical basolateral membranes by displacing [125I]insulin bound to the membranes and stimulating the tyrosine kinase activity of solubilized insulin receptors in a dose-dependent manner. In contrast, these antibodies had insulin antagonistic effects on the membrane (Ca2+ + Mg2+)ATPase activity. While insulin stimulated, both antibodies inhibited the ATPase basal activity in a dose-dependent manner. Furthermore, the stimulatory effect of insulin on the ATPase was completely abolished by the antibodies. Immunoglobulin fractions obtained from patient B10 in the clinically inactive phase of the disease and from pooled normal human sera did not affect basal or insulin-stimulated ATPase activity. The effects of insulin receptor antibodies on basal and insulin-stimulated (Ca2+ + Mg2+)ATPase activities were specific. The receptor antibody did not affect PTH-stimulated (Ca2+ + Mg2+) ATPase activity, nor did it affect other kidney basolateral membrane ATPase basal activities. The data reveal that insulin receptor antibodies have a direct regulatory effect on the plasma membrane (Ca2+ + Mg2+) ATPase. We suggest that the insulin antagonistic effects of the insulin receptor antibodies on the ATPase might explain in part the impaired insulin action in type B insulin resistance.

Polypeptide hormone receptor phosphorylation: is there a role in receptor-mediated endocytosis of human growth hormone?

To determine whether receptor phosphorylation is a critical step in the internalization of polypeptide hormones and their receptors, we have studied a model system wherein insulin stimulates phosphorylation of its receptor and is also internalized. Using insulin as a positive control, we found that it stimulated a partially purified plasma membrane preparation of IM-9 lymphocytes to autophosphorylate its receptor and to catalyze the phosphorylation of a tyrosine-containing substrate. The human GH (hGH) receptor of the IM-9 lymphocytes, when coupled to [125I]iodo-hGH, migrated as a 140,000-dalton protein on polyacrylamide gel electrophoresis. This protein, in contrast to the insulin receptor, was not phosphorylated by the addition of hGH, nor did hGH stimulate this preparation to phosphorylate the tyrosine-containing substrate poly-(GluNa,Tyr)4:1, casein, or histone f2b under a variety of conditions. We conclude that receptor phosphorylation is not a critical intermediate in the receptor-mediated endocytosis of hGH and probably other polypeptide hormones and growth factors.