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Biomedical subjects

R C Baxter

Publications and source records attributed to R C Baxter.

At least 253 records · Page 14Linked to original sources
PubMed1980

Simplified approach to confidence limited in radioimmunassay.

A simple method of calculating confidence limits for radioimmunoassay data is presented. The method involves the use of the within-assay variation in dose estimate of three routine quality-control specimens, measured in repeated assays, to estimate the confidence limits for results on unknown samples. Results for control specimens are combined by calculating the unique quadratic curve fitting a graph of within-assay standard deviation vs mean value for each control. This method requires no special data accumulation or advanced computing equipment. For cortisol, lutropin, and thyroxine radioimmunoassays, confidence limits calculated in this way have been compared with those calculated from the variance of the response variable "B/B0" in repeated standard curves. Both methods agree well with actual limits observed when plasma pools containing a wide range of hormone concentrations are assayed repeatedly.

Evaluation Studies as Topic↗
PubMed1979

Decrease in serum receptor-reactive somatomedin in diabetes.

Somatomedin in rat serum has been measured by a sensitive radioreceptor assay using 125I-labelled human somatomedin and human placental membrane. In rats made diabetic with strepotzotocin, receptor-reactive somatomedin levels were decrease by up to 75%. The decrease followed the time course of increasing serum glucose and occurred to the same extent in rats aged between 4 and 40 weeks. Endogenous serum receptor-reactive somatomedin appeared exclusively in high molecular weight fractions on gel chromatography. In diabetes the decreased somatomedin was due to a fall in this high molecular weight activity, but was not accompanied by a fall in somatomedin binding protein. These results suggest a role for insulin in maintaining serum somatomedin levels.

Animals↗
PubMed1979

Comparison of three iodination methods for human somatotropin.

Human somatotropin (growth hormone) iodinated by use of lactoperoxidase or Chloramine T added stoichiometrically has been compared with hormone iodinated by conventional Chloramine T method. The three preparations were indistinguishable, both in their stability to storage and in their suitability for use in radioimmunoassay. Degradation of tracer, as measured by decreasing precipitability with trichloroacetic acid, was found to be an unsatisfactory measure of immunoreactivity, because aggregates of high relative molecular mass formed during storage at--15 or--80 degrees C are less immunoreactive.

Growth Hormone↗
PubMed1978

Stimulation of protein synthesis in isolated hepatocytes by somatomedin.

Insulin (1 mU/ml) stimulated the incorporation of 14C-leucine into trichloroacetic acid-precipitable material by isolated hepatocytes from normal and hypophysectomized adult rats and 12-day-old rabbits. Somatomedin (200 ng/ml) purified from human plasma had an insulinlike effect in hepatocytes from hypophysectomized rats and baby rabbits but not from normal rats. This study suggests that, as well as being a site of somatomedin synthesis, the liver may be a target organ for this hormone.

Animals↗
PubMed1978

C-peptide secretion and insulin antibodies as determinants of stability in diabetes mellitus.

The relative significance of residual beta-cell secretory activity and human insulin antibodies in determining diabetic stability has been examined in 35 diabetic subjects. The response of plasma C-peptide immunoreactivity following 50 g oral glucose has been used as an index of beta-cell function. Glucose-stimulated C-peptide secretion was observed in 58% of stable diabetics, but in no labile diabetics. When present, C-peptide secretion following a glucose load in diabetics was of smaller amplitude and slower in onset, but more prolonged than in normal subjects. In secretors, stability of diabetes was significantly correlated with the magnitude of the C-peptide response. As a group, labile diabetics had lower insulin antibody levels than stable patients, but stability and antibody levels were not correlated in individual patients. In non-secretors there was no difference in antibody levels between the stable and labile groups. Neither the equilibrium binding affinities nor the dissociation rate constants differed significantly for antibodies from stable and labile diabetics. Thus stability of diabetes depends upon residual beta-cell secretory activity, but not on the concentration or binding characteristics of insulin antibodies.

Adolescent↗
PubMed1976

The dissociation of insulin from human insulin antibodies.

The dissociation of insulin from human insulin antibodies has been investigated using a technique that is rapid and does not require addition of excess unlabelled insulin. A slow (k1 = 2-10(-3) min-1) and a fast k2 = 4-10(-2) min-1) dissociating antibody component were identified in all studies. These have been shown to correspond, respectively, to the high and low affinity antibody components of equilibrium binding studies. The range of k1 and k2 values and their response to temperature change is small. Insulin resistance and stability of diabetes are not related to properties of antibody dissociation. Dissociation is faster in the presence of high (6-850 nM) insulin concentration due to increased binding to the fast dissociating component without change in the dissociation rate constants. When incubation time is increased beyond achievement of maximal binding there is a time-depent rise in binding to the slow dissociating component, with a concomitant fall in k1. The traditional concept that equilibrium is established at maximum binding requires further examination.

Antigen-Antibody Reactions↗
PubMed1976

Equilibrium binding studies of insulin antibodies in diabetic subjects.

Equilibrium binding of insulin to human insulin antibodies from diabetic subjects has been studied by two methods. Results obtained by using a nondissociating gel filtration assay differed from those obtained by a conventional competitive binding method. Both methods yield data consistent with two classes of insulin binding site, having association constants of approximately 10(9) and 10(7) liter/mol. The principal differences are the higher association constant and lower number of binding sites for the high-affinity binding component, observed with the gel filtration method. In the conventional competitive binding assay, damaged radioligand, dissociation of the binding complex, or limitations of ligand availability may be responsible for the erroneous results. Data from nine diabetic patients indicate that insulin resistance and stability of diabetes cannot be explained by the binding properties of insulin antibodies alone.

Binding Sites↗
PubMed1975

Involvement of cytosol proteins in oleate activation of rabbit liver fructose-1,6-diphosphatase.

Dialyzed rabbit liver cytosol was specifically freed of endogenous fructose-1,6-diphosphatase by immunoadsorption on a column of Sepharose-immobilized anti-fructose-1,6-diphosphatase. This material increased the specific activity of homogeneous enzyme to the maximal rate observed with EDTA and shifted the pH optimum from 8.4 to 7.4. With oleate or other fatty acids as activators, the hydrolysis of fructose-1,6-diphosphatase by enzyme, at neutral pH, showed nonlinear initial rates dropping to lower linear rates. Cytosol activator acted synergistically with oleate both to increase neutral enzyme activity and to maintain the high initial catalytic rates. After sucrose density centrifugation or gel filtration, the cytosol had no effect by itself, but still potentiated oleate activation. The factor was destroyed by treatment with subtilisin or trypsin, but all attempts to identify a unique protein component in cytosol were unsuccessful. The presence of Na dodecyl-SOJ, deoxycholate, or urea did not improve the resolution of the factor, but these compounds did lower the K50 for activation by cytosol. Since fatty acids are the only unique compounds which have been isolated from cytosol which activated fructose-1,6-diphosphatase, it appears that soluble proteins can act as natural carriers for the fatty acids. This was supported by the fact that both dialyzed rabbit alpha-globulins and muscle phosphofructokinase also acted synergistically with oleate in a manner similar to cytosol. Phosphatidic acid and phosphatidylserine activated fructose-1,6-diphosphatase, and their action was synergistic with oleate. Glutathione (1 mM) activated the enzyme 5-fold at pH 7.3 and its effects were additive with oleate and cytosol or alpha-globulins.

Albumins↗
PubMed1974

Comparative trial of benzhexol, amantadine, and levodopa in the treatment of Parkinson's disease.

Fourteen slightly disabled patients with Parkinsonism were treated separately with benzhexol, amantadine, and levodopa. Benzhexol and amantadine both gave a 15% reduction in functional disability and levodopa a 36% reduction. Benzhexol lessened the rigidity and improved the flexion of posture of Parkinson's disease, but had little or no effect on akinesia and tremor. Amantadine and levodopa caused improvement in all these symptoms. The combination of benzhexol and amantadine was as effective after four weeks of treatment as levodopa was after six months.

Aged↗