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Biomedical subjects

R I Misbin

Publications and source records attributed to R I Misbin.

At least 37 records · Page 2Linked to original sources
PubMed1985

Preferential binding of vasoactive intestinal peptide to hepatic nonparenchymal cells.

The binding of 125I-vasoactive intestinal peptide (125I-VIP) and 125I-insulin has been examined in highly enriched populations of rat hepatocytes and hepatic nonparenchymal cells. 125I-VIP bound to high-affinity sites (Ka = 1.7 X 10(9) M-1) in nonparenchymal cells. Specific binding in these cells was nearly fivefold greater than in hepatocytes (15.0 +/- 0.6% vs. 3.6 +/- 0.7% radioactivity bound per 4 X 10(5) cells). In contrast, 125I-insulin binding was similar in both cell populations (18.2 +/- 2.4% per 4 X 10(5) cells in hepatocytes vs. 17.1 +/- 1.0% in nonparenchymal cells). Glucagon and insulin had no effect on 125I-VIP binding in nonparenchymal cells. Secretin inhibited 125I-VIP binding but was only about 1% as potent as unlabeled VIP. VIP had no apparent effect on cAMP levels in either cell population, whereas glucagon increased cAMP levels in both cell types. Our findings suggest that VIP binds preferentially to hepatic nonparenchymal cells and that these cells are primarily responsible for the clearance of VIP from the portal circulation.

Animals↗
PubMed1984

Elevated L-xylulose concentrations in serum: a difference between type I and type II diabetes.

L-Xylulose, which can be derived from glucose directly or from mucopolysaccharide degradation, was measured in serum samples from 61 diabetics and 42 controls. All serum samples from the controls were negative for L-xylulose. Fifteen of 30 adult-onset diabetics, in contrast to only four of 31 juvenile-onset diabetics, had detectable L-xylulose levels. This difference between adult-onset and juvenile-onset diabetics was significant at the 0.001 level. Detectability of L-xylulose in serum did not appear to be influenced by the fasting mean or peak serum concentration of glucose. Mean serum concentrations of growth hormone did not correlate with L-xylulose levels. The reason for the variation of L-xylulose between type-I and type-II diabetic subjects could not be identified. We would postulate a variation in the degradation of glycosaminoglycan. These results support the view that type-I and type-II diabetes are different diseases.

Blood Glucose↗
PubMed1984

beta-Hydroxybutyrate increases the insulin sensitivity of adipocyte glucose transport at a postreceptor level.

The effect of insulin on glucose transport (2-deoxyglucose uptake) in adipocytes was measured in the absence and in the presence of 10 mM sodium-DL-beta-hydroxybutyrate. The ketone body had little or no effect on the basal or the maximally insulin-stimulated rate of transport. However, beta-hydroxybutyrate potentiated the effect of submaximal concentrations of insulin, i.e., it resulted in a leftward shift in the dose-response curve. The half-maximally effective concentration of insulin was decreased by approximately 30% from 0.58 ng/ml to 0.40 ng/ml. beta-Hydroxybutyrate caused a slight (approximately 10%) increase in 125I-insulin binding to the cells. To determine whether this small increase in insulin binding is responsible for the increased insulin sensitivity in the presence of the ketone, two mimickers of insulin action were used: a serum containing anti-insulin receptor antibodies and hydrogen peroxide. beta-Hydroxybutyrate increased the sensitivity of glucose transport to stimulation by the anti-receptor antibody, demonstrating that insulin itself does not have to be present. beta-Hydroxybutyrate also potentiated the effect of hydrogen peroxide (which acts at a level distal to the insulin receptor) even in cells that had been depleted of insulin receptors by trypsin treatment. Therefore, beta-hydroxybutyrate acts, at least partly, at a post-insulin receptor level. Adenosine increases the insulin sensitivity of adipocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed1984

The fate of insulin in rat hepatocytes. Evidence for the release of an immunologically active fragment.

We have investigated the fate of 125I-insulin after binding by rat hepatocytes. Approximately 30% of the bound radioactivity dissociated from the cells as intact 125I-insulin; approximately 56% dissociated as 125I- and 125I-Tyr. The remaining radioactivity was recovered as peptides that we postulate are intermediate products of insulin metabolism. Experiments were performed in the presence of chloroquine (0.1 mM), an agent known to inhibit the intracellular processing of 125I-insulin. As expected, chloroquine increased the amount of radioactivity recovered as intact 125I-insulin (P less than 0.005) and decreased the amount of 125I- and 125I-Tyr (P less than 0.005). In addition, chloroquine decreased the amount of one of the insulin peptides (P less than 0.005), but increased the amount of the other (P less than 0.01). These data suggest the presence of two pathways of insulin metabolism in rat hepatocytes, one of which is inhibited by chloroquine. We have found a second pathway by which insulin is degraded due to the removal of several amino acids from the carboxy-terminus of the B-chain. The resulting fragment bound poorly to insulin receptors on IM-9 cultured human lymphocytes, and probably has little if any biologic activity. However, this fragment bound well to anti-insulin antibody and constituted about 20% of the immunoreactive radioactivity that dissociated from the hepatocytes.

Animals↗
PubMed1983

Treatment of lactic acidosis with dichloroacetate.

We administered dichloroacetate, which prevents or reverses hyperlactatemia in animals and lowers plasma lactate levels in human beings, to 13 patients with lactic acidosis of various causes. All had hypotension, and their acidemia had resisted treatment with sodium bicarbonate. The metabolic effects of dichloroacetate were evaluated in 11 patients. In seven dichloroacetate significantly reduced the level of arterial blood lactate (P less than 0.005) from the base-line value and raised the levels of arterial blood bicarbonate (P less than 0.02) and arterial pH (P less than 0.005). In six of these seven, the acidemia resolved completely with therapy. In 10 of the 13 patients systolic blood pressure increased by 10 to 40 mm Hg, and 4 patients had a 21 per cent increase in cardiac output (P less than 0.02). Despite improvement in their lactic acidemia, all patients but one died of their underlying disease. No serious drug-related toxicity occurred. We conclude that dichloroacetate is a safe and effective adjunct in the treatment of patients with lactic acidosis, although the ultimate prognosis may depend on the underlying disease.

3-Hydroxybutyric Acid↗
PubMed1983

Insulin metabolism in rat hepatocytes. Evidence for generation of an insulin fragment missing a portion of the B chain involved in receptor binding.

Insulin metabolism by isolated rat hepatocytes was studied, utilizing A14 [125I]monoiodoinsulin, [3H]PheB1 semisynthetic insulin, and [3H]insulins synthesized by rat islets. Degradation was assessed by gel filtration, polyacrylamide gel electrophoresis, precipitation by anti-insulin antibody, and binding to specific insulin receptors on IM-9 human lymphocytes. When incubations were performed at 15 degrees C or less, insulin bound to hepatocytes remained intact for up to 2 h. At 37 degrees C we detected the generation of an insulin fragment with an apparent molecular weight of approximately 5000 whose electrophoretic mobility was greater than that of insulin. The fragment bound well to anti-insulin antibodies but poorly to insulin receptors. Information about the structure of the fragment was obtained by comparing the metabolism of [3H]PheB1 semisynthetic insulin with that of [3H]PheB1,24,25 insulin. The data suggest that the fragment contains PheB1 but is missing the PheB24 and PheB25. Treatment of the fragment with trypsin and carboxypeptidase B did not affect its electrophoretic mobility indicating that the fragment is also missing ArgB22. Incubation in the presence of 0.1 mM chloroquine led to accumulation of both intact insulin and the insulin fragment, suggesting that both are degraded by lysosomes. The results of this study suggest the presence of two pathways for insulin degradation in liver: a chloroquine-insensitive pathway by which a portion of the B chain consisting of at least 10 amino acids is removed and a chloroquine-sensitive pathway by which both insulin and the fragment are degraded.

Animals↗
PubMed1983

Resistance to subcutaneous and intramuscular insulin associated with deficiency of insulin-like growth factor (IGF) 2.

A diabetic patient is described whose serum was deficient in IGF 2. The patient responded appropriately to intravenous insulin but was resistant to subcutaneous and intramuscular insulin. His serum degraded insulin in vitro. This degradation was inhibited by IGF 2 and to a lesser extent by IGF 1 and insulin. We propose that this patient inactivated insulin at the injection site because of an insulin protease in his tissues that would normally be inhibited by serum IGF 2.

Adult↗
PubMed1983

Enteric release of vasoactive intestinal peptide after a peptone meal in the dog.

Vasoactive intestinal peptide (VIP) concentrations were measured by radioimmunoassay in plasma from portal and peripheral venous blood obtained from six alert, non-anesthetized dogs before and after gastric infusion of a 10% peptone meal. Mean basal portal and cephalic vein plasma VIP concentrations were 42 +/- 11.7 and 42 +/- 8.0 (S.E.M.) pg/ml, respectively. No significant changes in peripheral venous plasma VIP concentrations were noted after the peptone meal throughout the duration of the collection period. In contrast, however, the mean VIP concentration in portal plasma increased promptly after the peptone meal with a peak of 79 +/- 8.2 pg/ml (P less than 0.02) occurring 8 min after infusion of the meal. This was followed by a gradual decline in portal plasma VIP levels, with a return to prefeeding concentrations at 60 min (44 +/- 6.3 pg/ml). Results of these studies demonstrate that following gastric infusion of a peptone meal in the dog, portal, but not peripheral, plasma VIP concentrations increase significantly. Failure to detect augmentation of peripheral vein VIP levels after the meal is probably due to hepatic clearance of VIP.

Animals↗
PubMed1983

Inhibition of insulin degradation by insulin-like growth factors.

The effect of insulin-like growth factors (IGF 1 and IGF 2) on insulin degradation was studied with the use of a preparation of insulin protease from rat skeletal muscle. Insulin, IGF 1 and IGF 2 inhibited 125I-insulin degradation by this enzyme. IGF 2 was the most potent inhibitor and IGF 1 was the least potent. These results are similar to what has been reported previously for the insulin-degrading activity in the serum of a diabetic patient who was resistant to sc and im insulin. Insulin protease also degraded 125I-iodo IGF 1 and 125I-iodo IGF 2. 125I-iodo IGF 2 was degraded more rapidly than was 125I-iodo IGF 1. 125I-iodoinsulin was degraded more rapidly than 125I-iodo IGF 2. With all three peptides, immunoprecipitation was a more sensitive measure of degradation than was trichloroacetic acid precipitation. The results suggest that insulin protease may be responsible for the degradation of insulin-like growth factors as well as of insulin.

Animals↗
PubMed1983

Insulin binding to monocytes in obese patients treated with carbohydrate restriction and changes in physical activity.

Mean [125I]insulin binding to circulating monocytes was low (P less than 0.05 compared to normal controls) in nine obese patients on a weight-maintaining diet in which 45% of the calories were carbohydrate. On a 10% carbohydrate diet, insulin binding was normal in six of seven obese patients. Plasma insulin concentrations were elevated in obese patients on both diets. No correlation was found between insulin binding and plasma insulin concentration. Glucose intolerance and hyperinsulinemia were worsened by keeping the patients at rest and were improved by having the patients walk 3-4 miles/day. The change in physical activity had no effect on [125I]insulin binding to monocytes. We conclude that 1) insulin binding to monocytes in obese patients is generally low in patients on a carbohydrate-rich diet, but is normal in patients on carbohydrate-restricted diets; 2) down-regulation of insulin receptors does not necessarily occur in the presence of hyperinsulinemia: and 3) a walking program results in an improvement in glucose tolerance and hyperinsulinemia that is not associated with a change in insulin binding.

Adult↗
PubMed1982

Uptake of vasoactive intestinal peptide by rat liver.

We have investigated the uptake and degradation of vasoactive intestinal peptide (VIP) by rat livers. When liver was perfused with 125I-VIP, less than 20% of the radioactivity was recovered as intact peptide. 125I-VIp bound to specified high-affinity sites on isolated hepatocytes. Half-maximal inhibition of binding occurred at about 1 nM unlabeled VIP. Cell-bound 125I-VIP was degraded to low-molecular-weight products. The percent of 125I-VIP that was bound and degraded was approximately the same at both extremes of the range of VIP concentrations (25-250 pg/ml) reported in portal vein plasma. The lysosomotropic agent chloroquine inhibited 125I-VIP degradation and led to the accumulation of cell-bound 125I-VIP. We conclude that a) most of the VIP secreted from the gastrointestinal tract into portal blood is removed during its passage through the liver, b) VIP binds to specific high-affinity sites on hepatocytes and is probably internalized and degraded by lysosomes, and c) uptake of VIP by liver may serve to prevent the peptide from exerting deleterious systemic effects.

Animals↗
PubMed1981

Dietary regulation of insulin receptors in obesity.

Hospitalization of obese patients on a 45% carbohydrate diet resulted in a decrease of insulin binding to circulating monocytes. A further decrease was observed when the carbohydrate content was increased to 75% of total calories. When carbohydrate intake was restricted to 10% of total calories, insulin binding returned to normal. Total caloric intake was kept constant so that changes in insulin binding were not due to changes in body weight. Serum insulin levels were elevated in all obese patients regardless of what diet they were on receiving. The serum glucose level rose slightly in the patients on carbohydrate restriction despite the rise in insulin binding and persistance of hyperinsulinemia. I concluded: 1) factors other than a defect in insulin receptors contribute to insulin resistance in obesity; 2) although high insulin concentrations decrease insulin receptors in cells grown in vitro, cells from patients with hyperinsulinemia do not necessarily show decreased insulin binding; and 3) insulin binding is affected by the carbohydrate content of the diet and probably by other factors as well.

Adult↗
PubMed1981

Insulin degradation in serum of a patient with apparent insulin resistance.

A case is presented of a thin diabetic male who was resistant to large doses of sc and im insulin but responded to small dose of insulin given iv. His serum contained an enzyme that degraded [125I]insulin in vitro. We postulate that his apparent insulin resistance was due to inactivation of insulin at the injection site. We propose that the sera of patients with insulin resistance be tested for [125I]insulin-degrading activity as a possible means of identifying patients with this syndrome.

Adult↗
PubMed1980

Sex variation in dietary regulation of insulin receptors in man.

Hyperinsulinemia is associated with decreased insulin sensitivity and decreased binding of insulin to specific cellular receptors. In cells growth in culture, insulin directly decreases the concentration of its own receptor. Therefore, a negative feedback system has been proposed in which insulin sensitivity is regulated by insulin itself. In the present study, we investigated if nutritional factors could also regulate insulin binding to circulating monocytes in normal volunteers. The caloric content of their diet was kept constant and was calculated to maintain constant body weight. The diet consisted of 45% carbohydrate for the first 4 days and 75% carbohydrate for the next 7 days. In men, the high carbohydrate diet was associated with a 37% (P < 0.01) fall in insulin binding without change in serum or urinary levels of insulin. Despite the fall in insulin binding, no rise in serum glucose or free fatty acids was observed. In women, the high carbohydrate diet was not associated with any changes in insulin levels, insulin binding, glucose or fatty acids. We conclude that dietary regulation of insulin receptors in normal weight subjects is sex specific. Carbohydrate loading can decrease insulin binding in normal men by a mechanism that is not dependent on hyperinsulinemia.

Adult↗
PubMed1980

Binding and degradation of semisynthetic tritiated insulin by IM-9 cultured human lymphocytes.

Insulin was tritiated by semisynthetic replacement of the amino-terminal phenylalanine of the B chain with tritiated phenylalanine. At 15 degrees C, (3H) insulin bound to high affinity receptors on IM-9 cultured human lymphocytes with an affinity constant of about 3 x 10(9) M-1, The Scatchard plot was curvilinear. At 37 degrees C, maximal binding occurred after about 15 min of incubation. Binding fell thereafter due to degradation of insulin by the extracellular fluid. The major degradation product after 120 min coeluted with insulin from Sephadex G50 and was precipitated by anti-insulin antibody but to a lesser degree than intact insulin. It had little or no biologic activity as assessed by binding to IM-9 lymphocytes. The cell-associated radioactivity was also eluted as a single peak on Sephadex G-50. In contrast to the degradation product, this material retained its ability to bind to insulin receptors. We deduce that this cell-associated material contains the entire A chain, most of the B chain, and is probably native insulin. These data show that insulin bound to IM-9 lymphocytes remains biologically intact.

Antibodies↗