Vincent Marks

An improved glucose-oxidase method for determining blood C.S.F. and urine glucose levels

Abstract 1. 1. A simple, accurate, rapid method of determining glucose specifically in blood, C.S.F., and urine, using glucose-oxidase and peroxidase is described. 2. 2. A comparison between glucose and non-glucose reducing fractions before, during and after insulin administration is made, in which it is shown that non-glucose reducing substances in blood are diminished by insulin over a prolonged period. 3. 3. From the data presented it is suggested that the older non-specific methods of glucose estimation should be replaced by one of the newer enzyme methods.

The effect of unabsorbable carbohydrate on gut hormones. Modification of post-prandial GIP secretion by guar.

SummaryFive healthy volunteers and 6 diabetics were given a mixed test meal on two occasions — once with and once without 10 g guar flour. Addition of guar caused a 47% decrease in maximum post-prandial GIP levels, a 48% decrease in blood glucose and a 48% decrease in plasma insulin in normal subjects. In diabetics, addition of guar caused a 30% reduction in maximum post-prandial GIP and 58% decrease in blood glucose. Four normal and 6 diabetic subjects were given a predominantly carbohydrate meal, again with and without 10 g guar. Addition of guar caused a 78% decrease in blood glucose and a 59% decrease in plasma insulin in normal subjects. In diabetics addition of guar caused a 71% decrease in maximum post-prandial plasma GIP and a 68% decrease in blood glucose. Lowering of post-prandial blood glucose, plasma insulin and GIP levels by guar was statistically significant in every case. Addition of guar to the predominantly carbohydrate meal caused a decrease in total plasma GLI in both normal and diabetic subjects but reached statistical significance only in the normal subjects. There was a highly significant correlation (r=0.83; p<0.0005) between peak post-prandial insulin levels in normal subjects and the corresponding plasma GIP concentration. The reduction in GIP or GLI secretion may, therefore, be partly responsible for the smaller rise in plasma insulin observed in normal volunteers when guar is added to meals.

Interrelationship of Glucagon, Insulin and Glucose: The Insulinogenic Effect of Glucagon

Glucagon in doses of 0.25 or 1.0 mg. was injected rapidly, intravenously, into healthy normal subjects. There was a striking rise in arterial immunoreactive insulin levels within one minute of the start ot the injection before any change in arterial glucose concentration occurred Plasma insulin levels reached their peak within ten minutes and began to fall thereafter. In contrast, blood glucose levels were highest twenty to thirty minutes after the injection. A second glucagon injection during the hyperglycemic phase produced a larger rise in plasma insulin than the first. During constant infusions of smaller amounts of glucagon, the insulinogenic effect of glucagon was usually only apparent if blood glucose levels were raised. The effect of consecutive forty-minute intravenous infusions of glucagon (10μg./min.), glucose (0.5 gm./min.) and a glucagon-glucose (5μg. and 250 mg./min., respectively) on plasma insulin and arterio-venous blood glucose differences in six healthy normal subjects was studied. Plasma insulin levels were two to five times higher during glucose infusions alone, despite similar peak arterial blood glucose levels during the infusions. Similar results were obtained in other subjects during separate infusions of glucose and glucagon. Total body glucose clearance, judged by the rate of fall in arterial blood glucose levels, was faster after glucagon- than after glucose-induced hyperglycemia. Forearm A-V blood glucose differences were not obviously greater during glucagon, in spite of the higher plasma insulin levels, than during glucose infusions. Possible reasons for the failure of forearm A-V blood glucose differences to reflect accurately total peripheral glucose assimilation under these experimental conditions are discussed, and it is suggested that the co-existence of hyperglucagonemia and hyperinsulinemia may tend to favor incorporation of glucose into adipose tissue rather than muscle. Plasma glucagon levels were measured by immunoassay and the half-life was about ten minutes. The results provide evidence of a direct effect of glucagon upon insulin secretion. The suggestion is made that the insulinogenic effect of glucagon is physiological importance and is due to accelerated intra-β-cell glycogenolysis.

DRUG-INDUCED HYPOGLYCEMIA

Therapeutically administered antidiabetic drugs, notably insulin and the sulfonylureas, are undoubtedly the most common cause of hypoglycemia encountered in clinical practice. Nevertheless, an impressive list of other drugs can produce hypoglycemia unpredictably in seemingly healthy individuals in whom it may masquerade as spontaneous hypoglycemia. Unless the true cause is identified when the patient is first seen, fruitless and expensive overinvestigation may ensue. The most important drugs are discussed herein and brief mention made of those for which coincidence has not been eliminated.

Radioimmunoassay of gastric inhibitory polypeptide.

Summary A radioimmunoassay for the measurement of gastric inhibitory polypeptide (GIP) in unextracted plasma in man has been developed using a rabbit antiserum raised against porcine GIP. Porcine GIP was employed also as standard and to produce a 125I-labelled tracer. The assay was able to distinguish 110 pg/ml GIP from zero in plasma samples. Negligible cross-reactivity was demonstrated with cholecystokinin, insulin, pancreatic polypeptide, glucagon, secretin, and vasoactive intestinal polypeptide. The mean overnight fasting plasma GIP level in 28 normal subjects was 203 pg/ml (range: undetectable—420 pg/ml). Plasma GIP levels rose, within 45 minutes of eating a mixed meal, to a mean level of 1573 pg/ml.

Prolongation and enhancement of serum methotrexate concentrations by probenecid.

The disappearance of methotrexate (MTX) from the serum after an intravenous bolus injection and intravenous infusion was studied over 24 hours in eight and four patients respectively. Probenecid given at the same time as the bolus injection delayed the disappearance of MTX from the serum and resulted in enhanced concentrations throughout the 24 hours studied. At 24 hours the mean concentration was four times higher than in patients not given probenecid. Overall serum concentrations were even greater than those in patients who had received MTX by intravenous infusion. We suggest that smaller doses of MTX may be given and treatment costs thereby reduced if probenecid is given in addition.

INFLUENCE OF FOLIC ACID ON BLOOD-PHENYTOIN LEVELS

Abstract Correction of folic-acid therapy in patients receiving long-term anticonvulsant therapy was carried out under biochemical control of blood-anticonvulsant concentrations. Plasmaphenytoin levels fell significantly during folic-acid therapy. In one patient the fall was to below the therapeutic range and was associated with deterioration in fit control.

24‐HOUR PROFILES OF MELATONIN, CORTISOL, INSULIN, C‐PEPTIDE AND GIP FOLLOWING A MEAL AND SUBSEQUENT FASTING

Melatonin, free and total cortisol, insulin, C‐peptide and glucose‐dependent insulin‐releasing peptide (GIP) were measured in the plasma of twelve normal volunteers (eight women and four men), at hourly intervals for 24 h following a meal and subsequent fasting. One volunteer was excluded from calculations due to a possible effect of stress on melatonin secretion. Melatonin and cortisol showed the normal 24‐h variation with peak values at 0200–0500 h, and 0900 h respectively. Following post‐prandial stimulation, gut hormones remained basal throughout the sampling period. No significant relationship was found between 24‐h melatonin secretion and basal, or stimulated gut hormone secretion. Melatonin secretion did relate significantly to body weight, suggesting that data concerning pineal effects in endocrine physiology and pathology, and effective disease, should be reviewed in the light of these observations.

The role of immunoassay in the analysis of microcontaminants in water samples

Concentrations of natural and synthetic steroids and an anticancer drug (methotrexate) have been determined in water by adapting established immunoassay procedures. The limits of detection for the assays used were 10 ng/liter for norethisterone, 5 ng/liter for ethinyl estradiol and progesterone, and 6.25 ng/liter for methotrexate. Results below the level of detection were obtained in all the samples examined (8 river samples and 6 potable supply samples) except for 2 river samples (17 ng/liter) for norethisterone, and 1 river sample and 1 potable water sample for progesterone (6 ng/liter). A concentration of 1 microgram/liter of methotrexate was found in a sample of hospital effluent. There appears to be no evidence of adverse effects from reused water resources which may be contaminated from the normal use of such highly active therapeutic agents.

Abnormalities of GIP in Spontaneous Syndromes of Obesity and Diabetes in Mice

The role of GIP in the pathogenesis of spontaneous syndromes of obesity-diabetes wasexamined in ob/ob mice of the Aston stock and db/db mice of the C57BL/KsJ background. Compared with lean controls, fed adult ob/ob and db/db mice, respectively, exhibited 1.8- fold and 2.1-fold increases in body weight, 1.8-fold and 2.8-fold elevations of plasma glucose, and 15.4-fold and 5.6-fold elevations of plasma insulin. As indicatedby the relative magnitude of the hyperglycemia and hyperinsulinemia, db/db mice displayed a particularly severe form of diabetes. Plasma GIP concentrations of ob/ob and db/db mice were elevated 15.1-fold and 6.2- fold, respectively; the increments closely corresponded with the degrees of hyperinsulinemia. Small intestinal weight was increased 1.4-fold and 1.8-fold in ob/ob and db/db mice, respectively, but the intestinal GIP content expressed as μg/g intestine or μg/intestine was raised only in ob/ob mice (1.9-fold and 2.8- fold, respectively). Since glucose stimulation of insulin release is defective in both mutant strains, the results strongly implicate pathologically raised GIP concentrations in the hyperinsulinemia and related metabolic abnormalities of the obesity-diabetes syndromes. It is suggested that hypersecretion of GIP results in part from loss of normal feedback inhibition by endogenous insulin.