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R Chance

Publications and source records attributed to R Chance.

7 recordsLinked to original sources
PubMed1998

Basal activity profiles of NPH and [Nepsilon-palmitoyl Lys (B29)] human insulins in subjects with IDDM.

[Nepsilon-palmitoyl Lys (B29)] human insulin is a fatty acid-acylated derivative of insulin with extended action compared to unmodified insulin when infused intravenously (i.v.) secondary to its binding to circulating albumin. The duration and activity profile of the acylated (A) and NPH (B) insulins were assessed following subcutaneous (s.c.) doses of (A) 6 nmol/kg and (B) 1.2 nmol/kg (equivalent to 0.2 U/kg) in 9 subjects with IDDM. After overnight i.v. infusion of regular human insulin, morning glucose was (A) 6.9 +/- 0.1 and (B) 6.8 +/- 0.1 mmol/l. After the s.c. injection, i.v. human insulin or glucose was infused to maintain near-basal glycaemia and tracer glucose to assess hepatic glucose production (HGP). An activity profile was deduced for each study by expressing the glucose infusion rate at each time point, as a fraction (%) of the basal (measured) HGP, and the i.v. insulin infusion rate as a fraction (%) of the basal requirement. The two fractions are combined by adding the fractional glucose infusion rate and subtracting the fractional insulin infusion rate. Infusion rates of i.v. insulin in the morning were (A) 0.96 +/- 0.096 and (B) 1.22 +/- 0.09 pmol x kg(-1) x min(-1). After insulin injection, i.v. insulin requirements decreased and were below 10% of basal between 100 and 150 min. A constant activity profile of 0% represents a perfect substitution of the basal i.v. insulin infusion by the s.c. dose. The actual profile is defined by deviations from this (above) and was -17 +/- 11, 7 +/- 10, -9 +/- 6 and -18 +/- 18% for [Nepsilon-palmitoyl Lys (B29)] human insulin and 17 +/- 12, 5 +/- 6, -9 +/- 15, 22 +/- 18% for NPH insulin at 3, 6, 9 and 12 h after s.c. injection. HGP was similar for the two insulins, demonstrating similar metabolic actions and profiles both peripherally and at the liver.

Adult↗
PubMed1997

Prevention of vascular and neural dysfunction in diabetic rats by C-peptide.

C-peptide, a cleavage product from the processing of proinsulin to insulin, has been considered to possess little if any biological activity other than its participation in insulin synthesis. Injection of human C-peptide prevented or attenuated vascular and neural (electrophysiological) dysfunction and impaired Na+- and K+-dependent adenosine triphosphate activity in tissues of diabetic rats. Nonpolar amino acids in the midportion of the peptide were required for these biological effects. Synthetic reverse sequence (retro) and all-D-amino acid (enantio) C-peptides were equipotent to native C-peptide, which indicates that the effects of C-peptide on diabetic vascular and neural dysfunction were mediated by nonchiral interactions instead of stereospecific receptors or binding sites.

Amino Acid Sequence↗
PubMed1996

Report of the American Diabetes Association's Task Force on standardization of the insulin assay.

Recent large-scale epidemiological studies demonstrate that blood concentrations of immunoreactive insulin predict the development of NIDDM and IDDM and are associated with the risk of several degenerative diseases, such as coronary and peripheral vessel atherosclerosis, hypertension, and dyslipidemia. The reliability of these measurements is dependent on a biological assay that has not been well standardized between laboratories. Recognizing this, the American Diabetes Association organized a task force to assess comparability of blood insulin measurements between laboratories and to suggest techniques to improve comparability. The task force found that identical serum and plasma samples measured in different laboratories produced widely disparate values that were unacceptable for population comparisons. Use of a single reference standard did little to improve comparability. Assay characteristics such as linearity, recovery, accuracy, and cross-reactivity to proinsulin and its primary conversion intermediates varied among the laboratories, and they did not readily explain differences in the measurements made from assay to assay. Use of the same assay kit in different laboratories did not always ensure comparable measurements. Linear regression of assay results from one laboratory to an arbitrarily chosen reference assay greatly improved comparability and demonstrated the potential value in comparing each assay to a reference method. The task force report defines acceptable assay characteristics and proposes a three-step process of insulin assay proficiency and comparability. A central reference assay and ongoing sample exchange will be needed to allow reliable comparisons of insulin measurements made in different laboratories. Rigorous quality control and continuous quality improvement are needed to maintain reliability of the insulin measurement.

Diabetes Mellitus↗
PubMed1994

A problem we need not take for granted.

Continence problems are often assumed to be an inevitable part of old age. Individualised assessment may, however, provide information upon which a treatment plan can be based.

Aged↗
PubMed1989

Protein meal-stimulated pancreatic polypeptide secretion in Prader-Willi syndrome of adults.

Children with Prader-Willi syndrome (PWS) are characterized by obesity, hyperphagia, hypogonadism, and mental retardation with underlying hypothalamic dysfunction and are known to have blunted or absent pancreatic polypeptide (PP) secretion in response to protein meals. In this communication, adults (26 +/- 3 years of age) with PWS were compared with age-matched normal obese and normal weight controls in regards to plasma glucose, insulin, PP, cholecystokinin (CCK), cholesterol, and triglyceride after a high protein meal. Compared with normal weight controls, adults with PWS showed a smaller and delayed rise in plasma insulin, and relatively smaller and delayed PP elevation whereas obese controls revealed hyperglycemia, markedly higher insulin, and moderately higher PP, cholesterol, and triglyceride levels than those with PWS. There was a small increment of CCK levels after a protein meal in all groups of adults. After a protein meal, the molar ratio of PP to CCK doubled in normal weight and PWS groups, and this ratio tripled in the normal obese group, suggesting no reduced PP secretion in PWS in response to CCK stimulation. PP hyposecretion in PWS thus appears to be a part of multiple endocrinopathy associated with hypothalamic dysfunction.

Adult↗
PubMed1988

Determination of interchain crosslinkages in insulin B-chain dimers by fast atom bombardment mass spectrometry.

New methodology for identifying and locating crosslinkages in peptides is described. Pepsin is used to cleave insulin and B-chain dimers of insulin into fragments under conditions which retain the original peptide crosslinkages. After partial separation by HPLC, the peptides are analyzed by fast atom bombardment mass spectrometry (FABMS) to determine their molecular weights. The molecular weights of peptide fragments expected from the pepsin digests of human insulin and related model compounds are calculated from the amino acid sequence of the intact peptide. Digestion products are identified by matching their molecular weights, as determined by FABMS, with calculated molecular weights. Locations of interchain crosslinkages are deduced after the peptide fragments have been assigned to specific segments of the parent peptide. The validity of the method has been established by correctly identifying structurally important products in the pepsin digests of model compounds such as human, bovine, and porcine insulins. Procedures developed with the model compounds were used to identify crosslinkages in peptides of unknown structure isolated from an insulin A-chain/B-chain combination reaction mixture. Evidence is presented for formation of three different types of crosslinkages, disulfide, lanthionine, and sulfoxide.

Amino Acid Sequence↗