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Biomedical subjects

L C Harrison

Publications and source records attributed to L C Harrison.

At least 253 records · Page 14Linked to original sources
PubMed1979

Regulation of insulin receptors in normal and abnormal physiology in humans.

Insulin receptors in human tissue undergo marked changes in both their concentration and their affinity for insulin. In general, alterations in receptor affinity are associated with rapidly changing metabolic environments and can occur within hours, whereas alterations in receptor concentration appear to require longer time periods for their induction. The association of a given type of receptor alteration (i.e., change in affinity or concentration) with a given clinical state indicates the presence of distinct modulators of the insulin-receptor interaction. We have presented evidence for 2 specific modulators, i.e., insulin itself and anti-insulin-receptor antibodies. In several clinical states, especially those associated with changes in receptor affinity, receptor alterations are unrelated to either ambient insulin levels or anti-receptor antibodies, suggesting the presence of several as yet unknown mediators of the insulin receptor. The direct metabolic consequences of these receptor events are not well established. In several states, the receptor alteration correlated quite well with the clinical sensitivity of the whole organism to insulin, indirectly implicating the receptor as the major control point for insulin sensitivity. In contrast, specific examples were cited in which receptor events are not consonant with observed biologic responses to insulin, thereby suggesting a predominance of postreceptor processes. Finally, it should be emphasized that the study of hormone receptors and their relationship to disease states is in the formative stage. With new and improved methodology we hope we will be able to investigate the entire pathway of insulin action at its target tissues, from the initial receptor binding to the final biologic effect.

Acanthosis Nigricans↗
PubMed1978

The effects of digestive enzymes on characteristics of placental insulin receptor. Comparison of particulate and soluble receptor preparations.

The role of the surrounding membrane structure on the binding characteristics of the insulin receptor was studied by using several digestive enzymes. The effects observed with particulate membrane preparations are compared with those from soluble receptor preparations. beta-Galactosidase and neuraminidase had no effect on insulin binding to either particulate or soluble receptors from human placentae. Exposure to 2 units of phospholipase C/ml increased insulin binding to particulate membranes, but was without effect on the soluble receptor preparation. The increase in binding to particulate membranes was shown to be due to an increase in apparent receptor number. After 5 min exposure to 500 microgram of trypsin/ml there was an increase in insulin binding to the particulate membrane fraction, owing to an increase in receptor affinity. After 15 min exposure to this amount of trypsin, binding decreased, owing to a progressive decrease in receptor availability. In contrast, this concentration of trypsin had no effect on the solubilized receptor preparation. Because of the differential effects of phospholipase C and trypsin on the particulate compared with the solubilized receptor preparations, it is concluded that the effects of these enzymes were due to an effect on the surrounding membrane structure. Changes in receptor configuration due to alterations within the adjoining membrane provide a potential mechanism for mediating short-term alterations in receptor function.

Cell Membrane↗
PubMed1978

Extreme insulin resistance in ataxia telangiectasia: defect in affinity of insulin receptors.

The syndrome of ataxia telangiectasia is associated with glucose intolerance and insulin resistance. We examined the status of insulin receptors on circulating monocytes and on cultured fibroblasts from two siblings with ataxia telangiectasia and severe insulin resistance. 125I-insulin binding to monocytes of the two patients consistently demonstrated an 80 to 85 per cent decrease in receptor affinity. In contrast, the defect in receptor affinity was not expressed on the patients' cultured fibroblasts or on monocytes or fibroblasts obtained from unaffected family members. Whole plasma and immunoglobulin-enriched fractions of plasma from the patients inhibited the normal binding of insulin to its receptors on cultured human lymphocytes (IM -9 line) and on human placental membranes. We conclude that the insulin resistance in the two siblings with ataxia telangiectasia was associated with defects in the affinity of the receptors for insulin, probably caused by circulating inhibitors of insulin binding.

Acanthosis Nigricans↗
PubMed1978

Environmental and Seasonal Factors Affecting the Frost-induced Stage of Cold Acclimation in Cornus stolonifera Michx.

Stem tissues of red-osier dogwood (Cornus stolonifera Michx.) acclimated from -3 C to -40 or -50 C in 8 to 10 weeks under a short photoperiod (9 hours) and controlled temperature conditions. During the summer months plants did not acclimate as well as at other times. The sequence of day/night temperature regimes which induced maximum acclimation was 20/15 C for 5 to 6 weeks; 15/5 C for 2 to 3 weeks; 15/5 C plus 1 hour of frost per day for 1 week. The duration of exposure to each temperature regime influenced the rate and intensity of frost-induced acclimation. Less than 5 weeks of warm temperature preconditioning at 20/15 C reduced subsequent frost-induced acclimation. The inductive influence of frost on cold acclimation was additive over 5 days of repeated exposure, but its effects after the first exposure(s) were not immediate-requiring 1 to 4 days of 15/5 C following the frost treatments for the expression of the frost-induced acclimation to be manifest. There was a 75% increase in rRNA following 3 days of frost exposure and plants in an O(2)-free atmosphere during frost exposure failed to acclimate. The results suggest that seasonal acclimation behavior was due to endogenous rhythms rather than developmental stage, and that the frost-induced phase of acclimation involves aerobic metabolic processes.

Journal Article↗
PubMed1978

Freezing of water in red-osier dogwood stems in relation to cold hardiness.

Studies of stem water in red-osier dogwood (Cornus stolonifera Michx.) using nuclear magnetic resonance spectroscopy indicated that most freezing occurs at temperatures above -30 C in cold-hardy and tender stems. Hardy and tender stems had about the same amount of unfrozen water at -40 C (0.28 gram of water per gram dry weight). When hardy stems were slowly cooled below -20 C, the temperature below which little additional freezing occurs, they survived direct immersion in liquid N(2) (-196 C). Fully hardy samples not slowly precooled to at least -15 C did not survive direct immersion in liquid N(2). The results support the hypothesis that cooling rate is an unimportant factor in tissue survival at and below temperatures where there is little freezable water.

Journal Article↗
PubMed1978

The effect of solubilization on the properties of the insulin receptor of human placental membranes.

The insulin receptor for human placental membranes has been solubilized in Triton X-100 and its properties have been examined in detail. Binding of [125 I]iodoinsulin to the soluble receptor is markedly inhibited by increas-ng concentrations of Triton X-100, due to a fall in receptor affinity. In 0.02--0.10% Triton X-100, the soluble receptor exhibits all the essential characteristics of the intact or particulate receptor. These include strict specificity for insulin and its analogues, increase in steady state binding with decrease in temperature, a pH optimum at 7.8--8.0, and negatively cooperative site-site interactions. The initial association rate of [125 I]iodoinsulin and the soluble receptor is a direct function of temperature, but the level of steady-state binding is lower at higher temperatures due to a marked increase in dissociation rate. Scatchard binding plots are curvilinear and show a large increase in affinity at 4 C with no change in total binding capacity (R0); increased binding to the particulate placental membrane at 4 C is due chiefly to an increase in R3. Negative cooperatively in the soluble receptor has been confirmed by kinetic experiments; thus, the dissociation of [125I]iodoinsulin from the receptor in the presence of "infinite" dilution is accelerated in the presence of 10(-8) M unlabeled insulin. The apparent molecular weight of the placental receptor, determined by gel filtration on 6% agarose, is approximately 300,000. These studies show that the basic properties of the insulin receptor do not depend on it being an integral conponent of the cell membrane.

Female↗
PubMed1978

Werner's syndrome: a model of premature aging?

A 34 year-old woman with Werner's syndrome has been studied in the light of the current concept that this disorder is a model of premature aging. Endocrine function assays revealed an abnormal glucose tolerance and in vivo insulin insensitivity after prednisolone, and ovarian failure. Immune function assays revealed hypo-responsiveness in skin tests for delayed hypersensitivity, a poorly sustained IgG anti-body response after immunization with flagellin, and a low count of colony-forming T lymphocytes in blood. Cultured fibroblasts had a very limited capacity to replicate in vitro, in comparison with donors of similar age and, moreover, 85% of glucose-6-phosphate dehydrogenase in the patient's cultured fibroblasts was heat-stable at 60 degrees C compared with 100% for a healthy control. Cell receptors (for insulin) were examined by insulin binding to isolated fat-cells, with the finding that fat-cells were abnormally large for the patient's size, and their receptor density was low. The findings from the study point to a genetic defect in Werner's syndrome which, in its effect on particular tissues, may simulate features of aging, but the disease is not a true model of premature aging.

Adult↗
PubMed1977

Use of a computer-based postal questionnaire for the detection of hypothyroidism following radioiodine therapy for thyrotoxicosis.

A computer-processed postal questionnaire was devised to detect hypothyroidism in patients treated previously for thyrotoxicosis with radioiodine. In a study of 232 patients treated with 131I at the Royal Melbourne Hospital between four and ten years previously, the sum of symptomatic answers in the questionnaire was a sensitive discriminator of hypothyroidism, and allowed 80% of euthyroid patients to be excluded from further assessment. Questions concerned with general well-being and energy, voice and skin changes, showed the highest sensitivity and specificity. The combination of these questions alone was an effective means of identifying hypothyroidism, with a sensitivity and specificity comparable to the more sophisticated technique of discriminant function analysis. Hypothyroidism had an incidence of between 20% and 35% six to eight years after 131I therapy and was related to a smaller initial goitre size for a given dose of 131I. This postal questionnaire, in conjunction with a computer-based automatic recall system, promises to be an efficient and reliable screening tool for the detection of hypothyroidism in the increasing number of patients "at risk" following 131I therapy.

Australia↗
PubMed1976

Insulin sensitivity of adipose tissue in vitro and the response to exogenous insulin in obese human subjects.

The effect of varying concentrations of insulin on 1-14C-glucose conversion to 14CO2 was measured in subcutaneous adipose tissue samples obtained from 16 obese human subjects (10 nondiabetic, 6 diabetic). An index of insulin sensitivity in vitro, Kins, was calculated as the concentration of insulin stimulating one-half maximal 14CO2 production. An index of insulin sensitivity in vivo, Kitt, was calculated as the rate constant for decrease in blood glucose after rapid intravenous administration of 0.05 U/kg insulin. There was, over-all, a significant correlation between Kins and Kitt, indicating that insulin sensitivity of 1-14C-glucose oxidation by adipose tissue in vitro reflects the general state of sensitivity of glucose metabolism to insulin in vivo in obese human subjects. The mean values for both Kins and Kitt in the nondiabetic subjects were significantly different from those in the diabetic subjects, indicating greater sensitivity to insulin in the former group. The nondiabetic group was also distinguished by a significantly greater plasma insulin:blood glucose ratio in the oral glucose tolerance test. These results support the view that tissue insulin sensitivity as well as pancreatic beta cell response play an important role in determining glucose tolerance in obesity.

Adipose Tissue↗
PubMed1976

Cell size and glucose oxidation rate in adipose tissue from non-diabetic and diabetic obese human subjects.

1. The rate of oxidation of [1-14C]glucose to 14CO2 was examined in subcutaneous adipose tissue from fifteen obese non-diabetic subjects and from eleven obese maturity-onset diabetic patients. Production of 14CO2, measured in the basal state and in the presence of insulin, was significantly correlated with mean cell size in both the non-diabetic and the diabetic subjects, independent of age, relative weight and fasting plasma insulin concentration. 2. Comparison of the regressions of glucose oxidation rates on mean cell size indicated: (i) that insulin produced a significant increase in activity over the basal value in both groups, and (ii) that basal and insulin-stimulated activity were both significantly lower in diabetic than in non-diabetic adipose tissue.

Adipose Tissue↗
PubMed1976

Correlation between insulin receptor binding in isolated fat cells and insulin sensitivity in obese human subjects.

This study examined the relationship between receptor binding of insulin in a metabolically significant target tissue in vitro and sensitivity to insulin in vivo in obese human subjects. Specific insulin binding was measured at 24 degrees C in isolated enlarged fat cells obtained from 16 patients, by observing the effect of increasing concentrations of unlabeled insulin on the binding of [125I]insulin. Scratchard plots of the binding data were curvilinear with an upward concavity, similarity shaped, and essentially parallel. Kinetic studies on the dissociation of [125I]insulin from fat cells indicated that these curvilinear Scratchard plots could be explained by the presence of site:site interactions of the negative cooperative type. Differences in binding between individual patients were predominantly due to differences in the numbers of receptor sites whether expressed in relation to cell number, cell volume, or cell surface area. These findings were not accounted for by differences in [125I]insulin degradation. Acute exposure of adipose tissue to insulin in vitro had no significant effect on [125I]insulin binding to isolated cells. The number of receptor sites was directly correlated with insulin sensitivity in vivo, measured as the rate constant (Kitt) for the fall in blood glucose after intravenous insulin, and was inversely correlated with the level of fasting plasma insulin. These findings corroborate those from other studies using human mononuclear leukocytes and various tissues from the obese mouse, which indicate that decreased insulin binding is a characteristic feature of insulin resistance in obesity.

Adipose Tissue↗
PubMed1975

Effects of mazindol on carbohydrate and insulin metabolism in obesity.

Oral administration of a single dose of the anorectic agent mazindol to obese subjects led to a significant improvement in oral glucose tolerance and a concomitant reduction in insulin secretion, but had no effect on the blood glucose and plasma insulin responses to glucose given intravenously. Mazindol, when given to obese subjects in conjunction with a hypocaloric diet, was associated with progressive weight loss and reduction in the fasting levels of blood glucose, plasma insulin, serum triglyceride, and serum cholesterol. When oral glucose tolerance was retested after 16-20 wk, blood glucose and plasma insulin responses were significantly decreased compared with initial control values. It is concluded that one effect of mazindol, when given acutely, is to impair absorption of glucose from the gut. Changes in carbohydrate metabolism after chronic administration of mazindol are entirely consistent with weight loss, although a separate effect of the drug cannot be excluded.

Glucose↗
PubMedDate not supplied

The beta cell in autoimmune diabetes: many mechanisms and pathways of loss.

Death of pancreatic beta cells is the final step in the pathogenesis of type 1 diabetes before it becomes clinically apparent. Applying recent basic research about how cells die to the clinical problem of diabetes is a current opportunity and challenge. To date, perforin is the only factor definitely implicated in beta-cell killing in the non-obese diabetic (NOD) mouse model, although some perforin-deficient NOD mice develop diabetes. Our results suggest that other factors that cause beta-cell death remain to be identified.

Autoimmune Diseases↗