A double antibody immunoassay for glucagon

Comparative effect of human soluble insulin and insulin aspart upon hypoglycaemia-induced alterations in cardiac repolarization

AIMS

Sudden death in young diabetic patients has been associated with nocturnal hypoglycaemia perhaps as a result of cardiac dysrhythmias following abnormal cardiac repolarization during hypoglycaemia. It was therefore important to compare the effect of soluble human insulin (HI) and a rapid-acting insulin analogue, insulin aspart (IAsp), on these aspects of cardiac function.

METHODS

A total of 17 healthy males underwent identical hyperinsulinaemic hypoglycaemic clamps with blood glucose maintained at 5 mm for 30 min and reduced to 2.5 mm after an additional 30 min. Subjects received either HI or IAsp on two different occasions separated by 4-6 weeks. Regular measurements were made of two measures of cardiac repolarization, QT dispersion and QTc as well as of counter-regulatory hormones.

RESULTS

The blood glucose lowering effect did not differ between IAsp and HI and the clearance rates were similar (HI mean +/- SD 1.24 +/- 0.12 l h(-1) kg(-1), IAsp mean +/- s.d. 1.22 +/- 0.32 l h(-1) kg(-1)). There were similar significant increases but no difference between treatments in QTc after hypoglycaemia induced by either IAsp or HI (480 +/- 37 ms vs 480 +/- 25 ms; NS). However, QT dispersion during hypoglycaemia was less pronounced with IAsp than with HI (92 +/- 36 ms vs 107 +/- 42 ms; P < 0.05). Plasma adrenaline increased significantly and similarly after both insulins (initial and final concentration, HI, 0.23 +/- 0.01 to 4.87 +/- 0.48 nm, P < 0.001, IAsp, 0.24 +/- 0.01 to 4.99 +/- 0.48 nm, P < 0.001). Serum potassium decreased significantly but by a similar amount between the groups (initial and final concentration, HI, 4.18 +/- 0.3 to 4.2 +/- 0.2 mm, P < 0.001, IAsp, 4.2 +/- 0.3 to 4.2 +/- 0.3 mm, P < 0.001).

CONCLUSIONS

Soluble human insulin and insulin aspart had similar effects upon hypoglycaemia-induced alterations in cardiac repolarization, presumably because the effects of both regular insulin and insulin aspart on the sympathoadrenal response and potassium concentration were the same.

Symptomatic and counterregulatory hormonal responses to acute hypoglycaemia induced by insulin aspart and soluble human insulin in Type 1 diabetes

BACKGROUND

The aim of this study was to assess hypoglycaemia awareness with the insulin analogue, insulin aspart. The counterregulatory hormonal and symptomatic responses to hypoglycaemia induced by insulin aspart were compared with soluble human insulin in a double-blind, randomised, two-period crossover trial in patients with Type 1 diabetes. The primary objective was to compare the blood glucose threshold for autonomic activation during hypoglycaemia induced by insulin aspart and soluble human insulin. Secondary objectives were to compare the counterregulatory, symptomatic and physiological responses to hypoglycaemia.

METHODS

20 patients were screened, 17 were randomised and 16 completed the study. Acute hypoglycaemia was induced by intravenous infusion of insulin aspart or soluble human insulin (100 U ml(-1) at a rate of 2 mU kg(-1) min(-1)).

RESULTS

No statistical difference between insulin aspart and soluble human insulin was shown for the primary blood glucose endpoint; mean arterialised blood glucose concentrations (+/-SD) at the onset of autonomic activation were 1. 88+/-0.39 mmol L(-1) for insulin aspart and 1.89+/-0.43 mmol L(-1) for soluble human insulin (not significant). No statistical differences were observed between the two insulins for the secondary endpoints: counterregulatory hormonal responses, autonomic responses, hypoglycaemia symptom scores, cognitive function and blood glucose responses. No serious adverse events were reported during the study.

CONCLUSIONS

Insulin aspart and soluble human insulin elicit the same counterregulatory and symptomatic responses to acute hypoglycaemia in patients with Type 1 diabetes.

Acute hyperglycaemic effect of anaesthetic induction with thiopentone

The acute effects of thiopentone on plasma glucose concentration and regulation in humans have not been well described. We therefore examined the effect of a single dose (6 mg/kg) of thiopentone on plasma glucose, insulin, glucagon, adrenaline and noradrenaline in 16 healthy women undergoing elective abdominal surgery. To assess involvement of the neuroendocrine system in the response to thiopentone, half of the patients received labetalol prior to induction of anaesthesia. Thiopentone injection resulted in a 50% increase in plasma glucose levels (P < 0.001) in both labetalol-treated and non-treated patients 90 s following its administration. This was associated neither with significant increases in plasma glucagon, adrenaline and noradrenaline nor with a decline in plasma insulin. We conclude that acute hyperglycaemia following thiopentone is most likely the consequence of a non-adrenergically-mediated increase in hepatic glucose release.

Impaired glucose disposal following mild hypoglycemia in nondiabetic and type I diabetic humans

Insulin-mediated glucose disposal was studied immediately prior to and following moderate hypoglycemia in nondiabetic subjects and subjects with insulin-dependent (type I) diabetes mellitus (IDDM), the latter having varying epinephrine secretory capacities. Plasma insulin concentration was fixed throughout the study at approximately 300 to 400 pmol/L to avoid effects of waning insulin action and plasma glucose was clamped at either 5 mmol/L (euglycemic control) or at 3.1 mmol/L (hypoglycemic) periods of 120 minutes. Baseline (clamp 1) and postexperiment (clamp 2) periods were assessed for net glucose disposal (as a function of the exogenous glucose infusion rate) and glucose kinetics using 3H-glucose. In normal subjects, glucose disposal increased progressively by 132% during control studies but only by 57% with intervening hypoglycemia (P less than .005). Similarly, 33% during hypoglycemia, P less than .025). These changes were mediated by reduction of whole-body glucose uptake (rate of glucose disappearance [Rd], [3H]-3-glucose) and metabolic clearance rates with comparable suppression of hepatic glucose production in both groups. The increase in plasma free-fatty acids (FFA) following hypoglycemia was modest but greater in subjects with IDDM (P less than .01), whereas IDDM had reduced concentrations of epinephrine (P less than .01) and glucagon (P less than .005) during hypoglycemia. In subjects with IDDM but not in normal subjects, the change in posthypoglycemia glucose disposal was inversely correlated with the increase in plasma norepinephrine (R2 = .54, P less than .004) and epinephrine (R2 = .32, P less than .04). Glucose disposal did not correlate with other counterregulatory hormones, plasma FFA, or antecedent glycemic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin and glucagon releasing activity of coleonol (forskolin) and its effect on blood glucose level in normal and alloxan diabetic rats

Colenol, a diterpenoid isolated from the roots of Coleus forskohlii stimulates the release of insulin and glucagon from the islets both in vitro and in vivo. Colenol-stimulated release of glucagon from islets in vitro is much more pronounced as compared to that of insulin. Glucose concentration of 5.6 mM in the medium is required for the colenol stimulation of insulin release. Feeding of coleonol to alloxan diabetic rats cause 36.5% increase in blood glucose level as compared to alloxan diabetic control. Oral feeding of coleonol for 7 days to normal rats causes increase in blood glucose, serum insulin, glucagon and free fatty acid levels with corresponding increase in glucose-6-phosphatase activity and depletion of liver glycogen. Predominant stimulation of A-cells by coleonol is suggested for the above effects.

Selective stimulation of insulin secretion by CCK-4 analogues having N-terminal modifications

Synthetic analogues of CCK-4 in which Trp was replaced by D-Pro (peptide I), Thz (peptide II) and delta Pro (peptide III) have been studied for their insulin and glucagon releasing activities from the islets of Langerhans in vitro. Peptide I has been found to be the most potent insulin releaser among the three analogues and its activity is comparable to that of CCK-4. Unlike CCK-4, its three analogues (peptides I-III) do not stimulate the release of glucagon with basal concentration of glucose in the medium. However, with increasing glucose concentration, all the three analogues potentiate the glucose stimulus for insulin release.

Insulin like activity in (-) epicatechin

Water extract of the bark of plant of Pterocarpus marsupium Roxb is used as an antidiabetic drug in indigenous medicine in India. (-) Epicatechin, its active principle, has been found to be insulinogenic. The present in vitro study reports some insulin like activities of (-) epicatechin. Like insulin, (-) epicatechin stimulates oxygen uptake in fat cells and tissue slices of various organs, increases glycogen content of rat diaphragm in dose-dependent manner with corresponding increase in U14-C glucose uptake, and inhibits theophylline induced lipolysis in isolated fat pads in dose-dependent manner. Experiments on competitive binding of 125I-insulin and (-) epicatechin to liver cell plasma membrane indicate that insulin does not share binding site with (-) epicatechin. (-) Epicatechin at a concentration of up to 1 mM does not effect the release of glucagon from the islets in vitro. Thus, (-) epicatechin has insulinogenic as well as insulin like properties.

Effect of some novel synthetic analogues of CCK-4 on insulin and glucagon secretion

The biologic activities of three synthetic analogues of CCK-4 (Trp-Met-Asp-Phe-NH2) in which (i) the C-terminal residue Phe was N-methylated (peptide I); (ii) the C-terminal Phe residue was N-methylated and Ser is substituted for Met in position 2 (peptide II); (iii) Pro was substituted for Trp in position 1 and the C-terminal amino nitrogen was methylated (peptide III), have been described. Peptides I and II have been found to inhibit the release of both insulin and glucagon, while peptide III was found to be a potent releasing agent for insulin and an inhibitor for glucagon.

Synthetic analogs of cholecystokinin terminal tetrapeptide that stimulate insulin but not glucagon release from pancreatic islets

Two synthetic analogs of CCK-4, Glp-Met-Asp-Phe-NH2 (I) and Pro-Met-Asp-Phe-NH2 (II) reported earlier to stimulate insulin release from the isolated rat pancreatic islets in vitro at concentrations as low as 10(-10) M, have now been found to be totally ineffective as glucagon releasers at concentrations as high as 10(-6) M or higher. It is evident that the replacement of Trp in CCK-4 by Glp and Pro residues leads to peptides which exhibit insulin releasing activity without stimulating the release of glucagon.

Effects of substantia nigra lesions on the volumes of A, B, and D cells and the content of insulin and glucagon in the rat pancreas

The effects of substantia nigra lesions on the volume densities of islet cells and on the content of insulin and glucagon in the pancreas were examined using five groups of age-matched, Sprague-Dawley rats. Two groups received bilateral substantia nigra lesions using intrathecal injections of either a low (6 micrograms/hemisphere) or a high (12 micrograms/hemisphere) dose of 6-hydroxydopamine. Rats given sham lesions served as controls for the effects of the neurotoxic drug. These three groups, plus a fourth consisting of unoperated controls, were provided with a high-fat diet to minimize lesion-induced alterations of food intake and body weight. Eleven weeks after lesion placement, tissue was collected from all animals for the assessment of islet cell volume densities and the pancreatic content of insulin and glucagon. Plasma samples also were obtained to determine the levels of glucose, insulin, and glucagon. Data from those animals were compared with that obtained from a fifth group, termed "pre-lesion controls", sacrificed at the beginning of the experiment. Linear-scan morphometry documented an increase of B-cell volume density in the pancreas of non-lesioned rats over the 11-week period (p less than 0.05). However, the volume density of B cells in the pancreas of lesioned animals did not increase compared with that of pre-lesion controls. In terms of A or D cells, no significant differences of volume density were found between the five groups. Compared with that of the pre-lesion controls, pancreatic insulin and glucagon content increased in the lesioned and neurally-intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

A solid phase radioimmunoassay for pancreatic glucagon

A solid phase radioimmunoassay procedure has been applied for the determination of glucagon and some variables of the assay procedure were studied. The sensitivity of the assay was 10 pg of glucagon for samples assayed in triplicate. This assay method which has a high precision and is technically simple as compared with other radioimmunoassays, was found to be suitable for studies on glucagon release in vitro.

Early differentiation of glucagon-producing cells in embryonic pancreas: a possible developmental role for glucagon

Glucagon and insulin are first detectable at the onset of rat pancreas organogenesis. Initially, the specific activity of glucagon is approximately 100-fold higher than that of insulin. At this early stage, endocrine storage granules, similar to alpha granules, are identifiable in electron micrographs. The granule characteristics, as well as the relative hormone levels, suggest that the early population of differentiated endocrine cells is in fact composed of glucagon-producing (A) cells. This high level of glucagon is present in the embryo much earlier than the metabolic processes thought to be controlled by this hormone. Moreover, glucagon-producing cells may be the first endocrine cells to differentiate. Other known endocrine products accumulate later, during the terminal stages of organogenesis. These observations suggest that glucagon may have a regulatory function in early embryogenesis.

The development of the dorsal and ventral mammalian pancreas in vivo and in vitro

The origin, morphogenesis, and biochemical differentiation of the dorsal and ventral pancreas of the rat embryo have been investigated in order to ascertain the similarities and dissimilarities between the two lobes. We have utilized a culture system in which the primitive gut gives rise to a number of differentiated organs, including the dorsal and ventral pancreas. The two pancreases do not undergo fusion in these cultures, thus allowing independent analyses of the two lobes for comparison with in vivo results. The dorsal pancreas first appeared at the 23-25 somite stage while the ventral pancreas appeared approximately 12 hr later at the 29-30 somite stage. Guts from embryos as young as 12 somites were capable of developing both pancreases in vitro. In spite of the 12 hr difference between the times of their appearance, the dorsal and ventral pancreases exhibited identical patterns of morphological and biochemical differentiation. The two lobes contained the same exocrine enzymes and hormones, at similar levels, differing only in their glucagon content, the dorsal pancreas possessing a fivefold higher glucagon specific activity. The implications of these results are discussed.

Factors affecting the response to insulin in the normal subhuman pregnant primate

The concentrations of plasma glucose, free fatty acids, insulin, growth hormone, and placental prolactin in subhuman primate fetal and maternal plasma were examined following intravascular administration of insulin and glucagon to the fetus and mother. The neonatal plasma responses to these same stimuli were also examined. Fetal plasma glucose concentrations were minimally altered by direct fetal insulin injections, whereas neonatal glucose levels declined with similar injections. In both instances, however, plasma free fatty acid levels declined following insulin. When the amount of insulin given the fetus was increased, fetal plasma glucose concentrations did decline. Combined intravascular insulin injections and infusions in the mother were associated with a disappearance of the initial maternal to fetal plasma glucose concentration gradient and a nearly parallel fall in both maternal and fetal plasma glucose levels. It was concluded that insulin was biologically active in the fetus. Obtunded fetal plasma glucose responses to direct fetal insulin administration may be a function of placental transfer of glucose from the maternal pool. Maternal plasma placental prolactin and fetal plasma growth hormone levels were unchanged in the presence of sustained maternal and fetal hypoglycemia. However, neonatal plasma growht hormone levels did increase in response to hypoglycemia. The observed bidirectional placental barrier to transfer of radioisotopically labeled growth hormone indicated that fetal plasma growth hormone was solely of fetal origin. These data suggested further that a change in the growth hormone-releasing mechanism may occur from fetal to neonatal life. Direct maternal intravascular glucagon administration led to augmentation in both maternal and fetal plasma insulin and glucose levels. Direct fetal glucagon injections enhanced both maternal and fetal plasma insulin levels. These simultaneous changes in both plasma pools were consistent with the demonstration of a bidirectional placental transfer of radioisotopically labeled glucagon. The role of endogenously produced glucagon in these studies remains to be clarified.