Search PubMed⌕ Search

Biomedical subjects

C R Kahn

Publications and source records attributed to C R Kahn.

At least 397 records · Page 22Linked to original sources
PubMed1978

Direct demonstration that receptor crosslinking or aggregation is important in insulin action.

Exposure of adipocytes to antibodies to the insulin receptor results in a blockade of (125)I-labeled insulin binding, stimulation of glucose oxidation, and many more insulin-like effects. Allowing for differences in purity, antireceptor antibody is equipotent with insulin on a molar basis. Both the bivalent F(ab')(2) and monovalent Fab' fragments of the antireceptor antibody are fully active in inhibiting (125)I-labeled insulin binding. Bivalent F(ab')(2) also retains its insulin-like effects. In contrast, the monovalent Fab' loses almost all ability to stimulate glucose oxidation and acts as a competitive antagonist of insulin-stimulated glucose oxidation. Addition of anti-F(ab')(2) antisera, which crosslink the Fab'-receptor complexes, results in a restoration of the insulin-like activity of the antibody. Similarly, when cells are exposed to submaximal doses of insulin, addition of anti-insulin antibodies at low concentration enhances the biological activity of insulin. These data suggest that receptor occupancy by ligand is not sufficient for signal generation and that the insulin-like effects of antireceptor antibody (and perhaps insulin itself) require receptor aggregation or clustering. This aggregation, however, appears to be independent of microfilaments or microtubules because the insulin-like effects of antireceptor antibody, and in fact, of insulin itself, are unaffected by agents that are known to disrupt these structures.

Adipose Tissue↗
PubMed1978

125I-insulin binding to cultured human lymphocytes. Initial localization and fate of hormone determined by quantitative electron microscopic autoradiography.

Morphologic and biochemical studies indicate that the initial action of insulin is binding to a cell surface receptor. Whether further translocation of the hormone, or a product of the hormone, occurs is unclear and has not been investigated by direct means. To determine the fate of 125I-insulin bound to its receptor, we have examined the distribution of radioactivity by quantitative electron microscopic autoradiography. Cultured lymphocytes of the IM-9 cell line were incubated with 0.1 nM 125I-insulin at 15 degrees and 37 degreesC for incubation periods extending from 2 to 90 min. At 15 degreesC, grains localize to the plasma membane and there is no translocation as a function of time. At 37 degreesC, grains predominantly localize to the plasma membrane but there is a small shift in distribution to a distance of 300-700 nm from the plasma membrane. This small additional band component of irradiation extends to approximately to10--15% of the cell radius. When a morphometric analysis is applied to grains extending 300 nm and beyond from the plasma membrane, we find no preferential localization to any intracellular organelle. We interpret these data to indicate that in the cultured lymphocyte, labeled insulin initially localizes to the plasma membrane but as fuanction of time and increasing temperature there is a small but definite translocation of the hormone or a product of the hormone to a hihgly limited aea of the cell periphery.

Autoradiography↗
PubMed1978

Alterations in insulin binding induced by changes in vivo in the levels of glucocorticoids and growth hormone.

Previous studies have shown that the sensitivity of tissues to insulin is diminished in states of glucocorticoid and GH excess and is increased when these hormones are deficient. To evaluate the role of the insulin receptor in these states, we have studied [125I]insulin binding to purified liver plasma membranes obtained from rats with a variety of perturbations of both glucocorticoids and GH. Glucocorticoid excess was produced in rats by administration of ACTH (40 U/day for 4 days) or dexamethasone (1 mg/day for 4 days). This resulted in an insulin-resistant state. Associated with this insulin resistance, there was a 50-60% decrease in insulin binding to its specific receptors in liver. Conversely, adrenalectomy, which produces an increase in insulin sensitivity, was associated with an increase in insulin binding to liver. Computer-assisted Scatchard analysis using a negative cooperative model for the inulin-receptor interaction indicated that, in contrast to our findings with obesity, the changes in insulin binding in these states were most likely due entirely to changes in receptor affinity, with no change in receptor concentration. GH administration also produced mild insulin resistance and a decrease in receptor concentration. This was associated with a reciprocal increase in receptor affinity and thus, no major alteration in insulin binding occurred at low physiological insulin concentrations. Hypophysectomized rats, on the other hand, showed an increase in receptor concentration and a decrease in affinity, and GH treatment only partially corrected these changes. Rats implanted with the MtT tumor (which secretes ACTH, GH, and PRL) have the combined effects of excess glucocorticoids and GH and are very insulin resistant. Liver membranes prepared from these rats showed a decrease in insulin binding and receptor affinity similar to that observed in other states of glucocorticoid excess. Further, adrenalectomy of the tumor-bearing rats resulted in an increase in insulin binding despite the persistence of the elevated levels of GH, ACTH, and PRL. These findings suggest that alterations in insulin receptor affinity and number may play a major role in the states of altered insulin sensitivity which accompany glucocorticoid excess and deficiency, and follow hypophysectomy. In contrast, the insulin resistance associated with GH excess is mediated at either a site on the receptor distal to the insulin-binding site (i.e. transduction) or at one or more of the intracellular reactions important in insulin action.

Adrenalectomy↗
PubMed1978

Insulin resistance, acanthosis nigricans, and normal insulin receptors in a young woman: evidence for a postreceptor defect.

We have previously described a group of young females with virilization, acanthosis nigricans, insulin resistance, and markedly decreased binding of insulin to its receptor (syndrome of insulin resistance and acanthosis nigricans type A). The present report concerns a 15-yr-old female with clinical features indistinguishable from the type A patients, including virilization, acanthosis nigricans, and extreme resistance to endogenous and exogenous insulin. Insulin levels were 400-650 microU/ml while fasting and were over 2200 microU/ml when stimulated. Proinsulin was less than 10% of the total immunoassayable insulin. In distinct contrast to the type A patients, insulin receptors on cells from this patient were entirely normal on the basis of specificity, negative cooperativity, affinity, concentration, and interaction with antiinsulin receptor antibodies. These findings suggest the presence of an intracellular defect as the cause of the observed insulin resistance.

Acanthosis Nigricans↗
PubMed1978

The evolving clinical course of patients with insulin receptor autoantibodies: spontaneous remission or receptor proliferation with hypoglycemia.

Three patients with insulin resistance caused by autoantibodies to the insulin receptor were investigated serially over a 3-yr period. Major changes in carbohydrate metabolism, insulin receptor status, and titer of antireceptor antibodies were observed in each case. In one patient, normalization of glucose tolerance, insulin sensitivity, and receptor binding were associated with a spontaneous fall in the titer of antireceptor antibody. A second, more severely affected patient had two entirely distinct phase to her illness. The first, or hyperglycemic phase, was characterized by insulin resistance, negligible insulin binding to receptors on circulating monocytes, and high titers of circulating antireceptor antibodies. The second phase was characterized by refractory hypoglycemia, in association with proliferation of membrance insulin receptors; these occurred despite persistence of high titers of antireceptor antibody. An unusual heptic lesion, diffuse adenomatosis, was observed during this phase. A third patient showed features of both of the other patients, with spontaneous fall in antibody titer as well as a later phase of receptor proliferation. These studies demonstrate that patients with antibodies to insulin receptors may have a fluctuating clinical course. There may be spontaneous changes in antibody titers as well as independent changes in receptor concentration. Hypoglycemia and hepatic proliferation are newly recognized clinical sequelae in patients with this syndrome.

Adult↗
PubMed1977

Ectopic production of chorionic gonadotropin and its subunits by islet-cell tumors. A specific marker for malignancy.

We measured human chorionic gonadotropin (hCG) and its subunits in 76 patients with islet-cell tumors. Seventeen of 27 patients with functioning islet-cell carcinomas had elevated plasma levels of hCG or one of its subunits (hCG-alpha and hCG-beta). Secretion was often discordant; the most frequent finding was an elevated level of hCG-alpha alone. In one patient responding to streptozocin, changes in hCG-alpha correlated with the clinical course. Studies of tumor extracts suggested that the markers observed in the circulation were being produced in the tumor itself. In contrast, none of the 43 patients with benign disease or the six patients with nonfunctioning malignant tumors had elevated levels of hCG, hCG-alpha or hCG-beta. These data show that hCG and its subunits are prevalent and specific markers for islet-cell carcinoma, and suggest that ectopic secretion results from malignant derepression of the genome rather than overproduction by an aberrant "cell rest."

Adenoma, Islet Cell↗
PubMed1977

Autoantibodies to the insulin receptor. Effect on the insulin-receptor interaction in IM-9 lymphocytes.

The serum of some patients with insulin-resistant "diabetes" contains antibodies that bind to and block the cell membrane receptors for insulin. In this report, we have characterized the effects of the antireceptor antibodies on the interaction of (125)I-insulin with its receptor on the human lymphoblastoid cell line IM-9. Up to 95% of specific insulin binding can be inhibited by pretreatment of the cells with these immunoglobulins. The onset of the inhibitory effect is time- and temperature-dependent, and the effect is reversed extremely slowly if the cells are suspended in a large excess of antibody-free buffer. These features of antibody binding can be easily distinguished from those for insulin binding to its receptor. The inhibitory effect of the antibodies can be reversed by exposure of the cells to conditions known to elute surface immunoglobulins. The three antireceptor sera studied appear to alter the insulin-receptor interaction in different ways. Two antisera markedly reduce receptor affinity through combined effects on the insulin association and dissociation rates, and, additionally, have smaller effects on available receptor number. A third antiserum primarily affects available receptor number and has little effect on receptor affinity. All three antisera inhibit the capacity of insulin to promote negatively cooperative site-site interactions among insulin receptors. The data suggest that these autoantibodies to the insulin receptor bind to different determinants on the receptor and may therefore be useful as unique probes of insulin receptor structure and function.

Allosteric Regulation↗
PubMed1977

Effects of autoantibodies to the insulin receptor on isolated adipocytes. Studies of insulin binding and insulin action.

Autoantibodies to the insulin receptor have been detected in the sera of several patients with the Type B syndrome of insulin resistance and acanthosis nigricans. In this study we have used three of these sera (B-1, B-2, and B-3) as probes of the insulin receptor in isolated rat adipocytes. Preincubation of adipocytes with each of the three sera resulted in an inhibition of subsequent [(125)I]insulin binding. 50% inhibition of binding occurred with serum dilutions of 1:5 to 1:7,500. As in our previous studies with other tissues, Scatchard analysis of the insulin-binding data was curvilinear consistent with negative cooperativity. Computer analysis suggested that in each case the inhibition of binding was due to a decrease in receptor affinity rather than a change in available receptor number. In addition to the effects on insulin binding, adipocytes pretreated with antireceptor sera also showed alterations in biological responses. All three sera produced some stimulation of basal glucose oxidation. With serum B-3, maximal stimulation of glucose oxidation occurred at a serum concentration that inhibited binding by only 10-15%, whereas with serum B-2 the dilution curves for inhibition of binding and stimulation of glucose oxidation were superimposable. Serum B-1 behaved as a partial agonist; that is, it inhibited binding more effectively than it stimulated glucose oxidation. Cells pretreated with this serum in a concentration which inhibited binding by 80% also showed a five-fold shift to the right in the dose response of insulin-stimulated glucose oxidation, whereas spermine-stimulated glucose oxidation was unaffected. Serum B-2, which contained the highest titer of antireceptor antibodies, also stimulated 2-deoxy-glucose transport, as well as glucose incorporation into lipid and glycogen. Both the ability of the serum to inhibit binding and stimulate glucose utilization were enriched in purified immunoglobulin fractions and retained in the F(ab')(2) fragment of the IgG. In addition, the bioactivity was blocked by antihuman IgG but not by anti-insulin antibodies. Enzymatic digestion of adipocytes with trypsin resulted in a complete loss of insulin-stimulated bioactivity of serum B-3, but had only minor effects on the glucose oxidation produced by serum B-1 or B-2.These data suggest that the antibodies present in these three sera bind to different determinants on the insulin receptor. Thus, these antibodies may be useful probes of receptor structure and function.

Acanthosis Nigricans↗
PubMed1977

The insulin receptor of the turkey erythrocyte: similarity to mammalian insulin receptors.

Avian erythrocytes possess insulin receptors which have binding properties that are virtually identical to those of the well studied mammalian insulin receptors. The affinity for porcine insulin was identical for the turkey and mammalian receptors over the entire range of insulin concentrations, as was the affinity of each of four insulin analogues which differed 300-fold in biological potency. Insulin induced acceleration of dissociation (i.e., the negatively cooperativite site-site interaction) was indistinguishable over a 10(6) range of insulin concentrations. Sharp pH dependence of binding was identical for turkey and mammalian receptors. The effects of temperature on association, dissociation and steady state binding were also identical. Thus, although birds and mammals have evolved separately for 300 million years there has been little change in the properties of the insulin receptor over this time period.

Allosteric Regulation↗
PubMed1977

Adriamycin therapy for advanced insulinoma.

Two patients with advanced metastatic insulinoma are presented. Both failed to respond to streptozotocin and were refractory to other forms of chemotherapy. Therapy with adriamycin (Patient No. 1) and adriamycin plus 5-fluorouracil (Patient No. 2) led to significant decreases in insulin levels or measurable disease and both patients had clinical remissions lasting 5 to 7 months. Adriamycin may be effective in patients with advanced insulinoma unresponsive to conventional chemotherapy.

Adenoma, Islet Cell↗
PubMed1977

Receptors for peptide hormones. New insights into the pathophysiology of disease states in man.

The first step in the action of polypeptide hormones and many neurotransmitters is binding to receptor sites on the plasma membrane of the cell. These receptors are usually complex, high molecular weight proteins. Using a variety of receptor preparations and radioactively labeled hormones, radioreceptor assays for several hormones have been developed. These have allowed for assay of hormones for which no immunoassay exists. Such assays have shown increased levels of NSILA-s (an insulin-like peptide) in patients with nonpancreatic tumors and hypoglycemia. In disease states, the number or affinity of hormone receptors may be altered, leading to hormone resistant states such as the insulin resistance of obesity. A major factor regulating receptor concentration is the hormone itself. Several hormones seem to accelerate inactivation of their own receptors. Antibodies to membrane receptors are produced in at least three diseases and cause hormone resistance or mimic states of hormone excess.

Acanthosis Nigricans↗
PubMed1976

Insulin-induced dissociation of its receptor into subunits: possible molecular concomitant of negative cooperativity.

The detergent-solubilized avian insulin receptor retains negative cooperativity and other binding properties of the membrane bound form. On gel filtration the receptor elutes as a single peak with a Stokes radius of 72 A. Preincubation of the receptor with low levels of insulin leads to the formation of a second, smaller form with a Stokes radius of 40 A. The percent of receptor in this second peak is proportional to the insulin concentration and correlates well with the insulin-induced increase in dissociation rate (negative cooperativity). Both the isolated high molecular weight and the isolated low-molecular-weight forms of the receptor re-equilibrate in the presence of insulin and, upon refiltration of either isolated peak, both forms of the receptor are obtained. These results are compatible with a model of the insulin receptor in which a tetrameric form can dissociate to a monomeric form as a concomitant of negative cooperativity.

Allosteric Regulation↗
PubMed1976

The insulin receptor of the turkey erythrocyte. Characterization of the membrane-bound receptor.

The insulin receptor of the turkey erythrocyte has previously been shown to be very similar to that of the mammalian insulin receptors. As a first step in the isolation of this receptor a highly purified plasma membrane fraction has been prepared. The binding characteristics of the purified membrane-bound receptor were identical to those found with intact erythrocytes, but the membrane preparation had very little insulin-degrading activity. Isolation of the membrane by the methods described gave a 100-fold purification of the insulin receptor with 67% yield.

Animals↗