Showing papers on "Insulin published in 1968"

Dynamics of Insulin Secretion by the Perfused Rat Pancreas

Abstract: The dynamics of insulin release in response to relatively long infusions of glucose were studied in the isolated perfused rat pancreas. Insulin secretion was determined by immunochemical assay of the total portal vein effluent. Histological examination of the perfused pancreases and measurement of oxygen consumption by these tissues indicated that optimal physiological conditions were used. It was observed that, when glucose was infused for a period of approximately 1 hr into a perfused pancreas, there appeared 2 distinctly different phases of insulin release. There was an early, or rapid, release of insulin which subsided within approximately 2 min, followed by a late, or slow release phase which continually increased in rate until termination of the glucose infusion. The contribution of newly synthesized insulin to either phase was determined by comparing the insulin release by normal control preparations to that by preparations which were treated with puromycin. Incorporation of L-valine-14C was used a...

The role of adipose cell size and adipose tissue insulin sensitivity in the carbohydrate intolerance of human obesity.

Abstract: Glucose metabolism and insulin sensitivity of isolated human adipose tissue was studied as a function of adipose cell size and number. Glucose metabolism by these tissues was closely related to the number of cells in the fragment, irrespective of cell size. Adipose cells of obese individuals metabolized glucose to carbon dioxide and triglyceride at rates similar to adipose cells of nonobese subjects. In contrast, insulin responsiveness of adipose tissue was dependent upon adipose cell size. The larger its adipose cells the less insulin sensitive was the tissue. Thus, adipose tissue of obese subjects, with enlarged cells, showed a diminished response to insulin. After weight loss and reduction in adipose cell size, insulin sensitivity of the adipose tissue of obese patients was restored to normal. When adipose tissue of obese individuals showed impaired responsiveness to insulin, their plasma insulin levels, after oral glucose, were elevated. Weight loss and reduction in adipose cell size restored plasma insulin concentration to normal, concomitant with the return of normal tissue insulin sensitivity.

New hypothesis of insulin secretion.

Abstract: RELEASE of insulin from beta cells of the islets of Langer-hans occurs as a result of the movement of secretory granules to the surface of the cells. Here the membranous sacs encasing the granules fuse with the plasma membrane, rupture and liberate the granules into the extracellular space1. This process is called emiocytosis. Although glucose represents the most important physiologic stimulus for the release of insulin from the beta cells, it has been shown recently that the rates of secretion of insulin are also altered in the presence of a wide variety of other agents2. So far, little information is available concerning the relationship between the biochemical effects of these agents and the process of emiocytosis. We suggest here a working hypothesis for the events which occur between biochemical stimulation and the liberation of secretory granules into the extracellular space.

Reversible blocking of amino groups with citraconic anhydride.

Abstract: Butler, Harris, Hartley & Leberman (1967) showed that maleic anhydride could be used for the reversible blocking of amino groups. The maleyl group could be removed because the protonated form of the free carboxyl group catalysed the hydrolysis of the amide bond, presumably by intramolecular general acid catalysis (cf. Bender, Chow & Chloupek, 1958). The present paper reports the effects of introducing methyl groups into the molecule of maleic anhydride. 2,3-Dimethylmaleic anhydride. We had wished to investigate whether the use of maleylation to introduce glyoxyloyl groups (Dixon, 1968) could be extended to the introduction of pyruvoyl groups. We therefore treated arginine with 2,3-dimethylmaleic anhydride (Fluka A.-G., Buchs, Switzerland) as follows. To a solution of arginine hydrochloride (5M) in water was added, with stirring, dimethylmaleic anhydride to a final concentration of 5-5m, and the pH was maintained at 8 by the addition of N-NaOH. Uptake ofbase ceased after about an hour and suitable samples were then applied to paper for high-voltage electrophoresis in the buffer systems used previously (Perham, 1967). Material was detected on the paper by means of the ninhydrincadmium reagent (Heilmann, Barrollier & Watzke, 1957) and also by the Sakaguchi reaction (Jepson & Smith, 1953). It was immediately apparent that arginine alone and no product could be detected after electrophoresis at pH 3 5, but that at pH 6 5

Porcine Proinsulin: Characterization and Amino Acid Sequence

Abstract: Proinsulin in nearly homogeneous form has been isolated from a preparation of porcine insulin. A molecular weight close to 9100 was calculated from the amino acid composition and from sedimentation-equilibrium studies. Through the action of trypsin this single-chain protein is transformed to desalanine insulin by cleavage of a polypeptide chain connecting the carboxy-terminus of the B chain to the amino-terminus of the A chain of insulin. The amino acid sequence of this connecting peptide was found to be Arg-Arg-Glu-Ala-Gln-Asn-Pro-Gln-Ala-Gly-Ala-Val-Glu-Leu-Gly-Gly-Gly-Leu-Gly-Gly-Leu-Gln-Ala-Leu-Ala-Leu-Glu-Gly-Pro-Pro-Gln-Lys-Arg.

Growth Hormone and Insulin Levels in Weanling Rats with Ventromedial Hypothalamic Lesions

Abstract: The effects of bilateral stereotactic electrolytic lesions limited to the ventromedial nucleus (VMN) in weanling female rats were studied with respect to growth, pituitary and plasma growth hormone levels, nutrition and plasma levels of glucose and insulin. The following were observed as a result of VMN lesions: 1) a marked decrease in linear growth with less pronounced changes in body weight, 2) an increase in carcass fat despite no increase in food intake, 3) decreased pituitary growth hormone content and plasma growth hormone levels as measured by radioimmunoassay, 4) increased plasma insulin levels and visible lipemia despite minimal changes in plasma glucose, 5) incomplete suppression of the hyperinsulinemia toward control levels by fasting. It is suggested that the ventromedial nucleus exerts a significant control over growth hormone secretion, presumably through a growth hormone releasing factor, and that its destruction results in growth impairment secondary to a deficiency in growth hormone secre...

Potassium ions and the secretion of insulin by islets of Langerhans incubated in vitro.

Abstract: 1. A method was devised for the isolation of islets of Langerhans from rabbit pancreas by collagenase digestion in order to study the influx and efflux of K(+) in islets during insulin secretion. 2. Glucose-induced insulin release was accompanied by an increased rate of uptake of (42)K(+) by the islets of Langerhans, though this was not the case for secretion in response to tolbutamide. Ouabain significantly inhibited the uptake of (42)K(+) by islet tissue. 3. No significant increase in the rate of efflux of (42)K(+) was demonstrated during active insulin secretion. 4. Slices of rabbit pancreas were incubated in media of different K(+) content, and rates of insulin release were determined. Alteration of the K(+) concentration of the medium between 3 and 8mm had no effect on the rate of insulin release by pancreas slices. However, decrease of the K(+) concentration to 1mm resulted in inhibition of secretion in response to both glucose and to tolbutamide. Conversely, an increase in K(+) concentration increased rates of insulin release in response to both these stimuli. 5. It is concluded that, though unphysiological concentrations of K(+) may influence the secretion of insulin, fluxes of K(+) in the islets do not appear to be important in the initiation of insulin secretion.

Isolation and characterization of chicken insulin.

Abstract: A method is described for isolation of insulin from chicken pancreas which makes use of modifications of established procedures to deal with the low insulin content of the tissue and permits isolation of significant quantities of the hormone. The insulin isolated is essentially homogeneous by paper chromatography and polyacrylamide gel electrophoresis. The amino acid composition of the insulin and of the separated A and B chains is consistent with the known amino acid sequence of chicken insulin. (Endocrinology 83: 1323, 1968)

Adrenergic receptor control mechanism for growth hormone secretion

Abstract: The influence of catecholamines on growth hormone secretion has been difficult to establish previously, possibly because of the suppressive effect of the induced hyperglycemia on growth hormone concentrations. In this study, an adrenergic receptor control mechanism for human growth hormone (HGH) secretion was uncovered by studying the effects of alpha and beta receptor blockade on insulin-induced growth hormone elevations in volunteer subjects. Alpha adrenergic blockade with phentolamine during insulin hypoglycemia, 0.1 U/kg, inhibited growth hormon elevations to 30-50% of values in the same subjects during insulin hypoglycemia without adrenergic blockade. More complete inhibition by phentolamine could not be demonstrated at a lower dose of insulin (0.05 U/kg). Beta adrenergic blockade with propranolol during insulin hypoglycemia significantly enhanced HGH concentrations in paired experiments. The inhibiting effect of alpha adrenergic receptor blockade on HGH concentrations could not be attributed to differences in blood glucose or free fatty acid values; however, more prolonged hypoglycemia and lower plasma free fatty acid values may have been a factor in the greater HGH concentrations observed during beta blockade. In the absence of insulin induced hypoglycemia, neither alpha nor beta adrenergic receptor blockade had a detectable effect on HGH concentrations. Theophylline, an inhibitor of cyclic 3′5′-AMP phosphodiesterase activity, also failed to alter plasma HGH concentrations. These studies demonstrate a stimulatory effect of alpha receptors and a possible inhibitory effect of beta receptors on growth hormone secretion.

Control of glycogen levels in brain.

Abstract: — Prolonged (6 hr) anaesthesia with phenobarbital in mice or rats results in a doubling or tripling of brain glycogen. Increases were also observed if high levels of plasma glucose were maintained for 6 hr. In alloxan diabetes brain glycogen was not elevated in spite of the high plasma glucose concentrations. However, administration of insulin to such diabetic animals, together with enough glucose to maintain high plasma levels, resulted in at least a doubling of brain glycogen in 6 hr. Phenobarbital can still increase brain glycogen in diabetic animals. In all of the conditions associated with increased glycogen deposition, increases were found in the ratio of brain glucose to plasma glucose. Cerebral glucose-6-P levels were also increased whereas there were no substantial changes in levels of UDP-glucose or glucose-1,6-diphosphate.

Study of the Relationship Between Glucose and Insulin Responses to an Oral Glucose Load in Man

Abstract: Oral glucose tolerance tests have been performed on 125 patients, and the ensuing changes in plasma glucose and insulin concentrations have been measured. The possible effects of factors which could modify the nature of these responses (obesity, age, sex, family history of diabetes, and indications for performing the tolerance test) have been extensively evaluated. None of these variables were found to have a statistically significant effect on the plasma glucose and insulin responses. Two general relationships between glucose and insulin responses have been defined within the population studied. One, based on the quantitative aspects of the glucose and insulin responses, indicated that there was at first an increase, and then, a decrease in the insulin response to progressive degrees of hyperglycemia. The second relationship was independent of the absolute concentrations of either glucose and insulin, and states that the pattern of glucose response during the three hours of the tolerance test determines the pattern of the insulin response during this same time interval.

Characterization of response of circulating glucagon to intraduodenal and intravenous administration of amino acids

Abstract: Studies were carried out to determine if hyperaminoacidemia stimulates the secretion of pancreatic glucagon, and, if so, to evaluate the effect of endogenous and exogenous pancreozymin and of hyperglycemia upon this response. The intravenous administration to 16 dogs of 1 g/kg of a 10 amino acid mixture over a 60 min period raised amino nitrogen to a mean level of 13.5 mg/100 ml; mean pancreaticoduodenal vein insulin rose from 84 to 459 muU/ml and glucagon from 1.1 to 2.7 mmug/ml. Further augmentation of both insulin and glucagon secretion was achieved during hyperaminoacidemia by infusing pancreozymin. Since endogenous pancreozymin is known to be stimulated by amino acids in the gut, it seemed possible that intraduodenal loading of amino acids would elicit a greater insulin and glucagon response than could be explained by the accompanying hyperaminoacidemia. The intraduodenal administration of 1 g/kg of the amino acid mixture was followed by substantial hyperinsulinemia and hyperglucagonemia, which frequently anticipated the hyperaminoacidemia, and in many of the dogs the ratio of hormone rise to amino nitrogen rise was greater after intraduodenal than after the intravenous route of amino acid administration in the same animal. Intraduodenal administration of amino acids did not cause measurable release of intestinal glucagon-like immunoreactivity into the mesenteric vein plasma. Hyperglycemia induced by constant glucose infusion prevented aminogenic hyperglucagonemia and even suppressed the augmenting action of pancreozymin; sudden termination of the infusion with continued amino acid infusion was associated with a striking rise in glucagon. It is concluded (a) that hyperaminoacidemia stimulates pancreatic glucagon secretion, (b) that aminogenic hyperglucagonemia is augmented by the infusion of pancreozymin, (c) that intraduodenal administration of amino acids stimulates pancreatic glucagon secretion without measurable release of glucagon-like immunoreactivity into the mesenteric vein, and (d) that hyperglycemia prevents aminogenic hyperglucagonemia even during augmentation with pancreozymin. This conclusion suggests that the prevention of hypoglycemia during amino acid-induced insulin secretion may be an important function of glucagon.

The role of sodium and potassium in insulin secretion from rabbit pancreas.

Abstract: 1. Insulin secretion from pieces of rabbit pancreas incubated in vitro was studied in media of different ionic composition and in response to different substances added to the media.2. Experiments were performed which demonstrated that a sodium pump played a role in insulin secretion and that inhibition of the pump by ouabain, or by the omission of extracellular potassium, stimulated insulin secretion.3. A rise in extracellular potassium concentration stimulated insulin secretion independently of changes in the osmolarity or sodium or chloride concentration of the incubation medium.4. The role of extracellular sodium in insulin secretion was investigated. Extracellular sodium was a pre-requisite for insulin secretion stimulated by glucose, glucagon, L-leucine, tolbutamide, potassium or ouabain.5. The presence of 3.3 mM glucose in the incubation medium was not essential for the stimulation of insulin secretion by L-leucine, tolbutamide or ouabain. Glucagon did not stimulate insulin secretion in the presence of 3.3 mM glucose but did so in the presence of 16.5 mM glucose.6. The results obtained in these experiments suggested that a transmembrane sodium flux probably in the beta cell was a fundamental event in the stimulation of insulin secretion by diverse stimuli.

Effect of short-chain fatty acids on plasma insulin in ruminant and nonruminant species.

Abstract: Regulation of plasma insulin levels in the sheep, cow, rat, rabbit and pig was investigated utilizing a double antibody radio-immunoassay In the sheep, infusion of the rumen metabolites, propionate and butyrate, increased plasma insulin levels approximately 4-fold and 14-fold, respectively, without affecting plasma glucose All fatty acids containing 3–8 carbon atoms stimulated insulin production, valerate being the most effective Acetate, aceto-acetate and beta-hydroxybutyrate had no effect on plasma insulin Infusion of glucose was much less effective than propionate, butyrate or valerate and there was no correlation between fasting glucose levels and fasting plasma insulin Infusion of propionate into rats, rabbits or pigs had no effect on the plasma insulin, whereas both propionate and butyrate provoked a rise in plasma insulin in the cow It was concluded that propionate and butyrate are stimulators of insulin secretion in the sheep and cow but not of nonruminant species (Endocrinology 83: 118, 1968)

Insulin: Intestinal Absorption as Water-in-Oil-in-Water Emulsions

Abstract: PREVIOUS reports have indicated intestinal absorption of insulin in the presence of alcohol1, saponins2, quinine3 or proteolytic inhibitors4,5. These data are often of questionable significance and are difficult to confirm. It has been generally accepted that insulin does not exhibit hypoglycaemic activity when administered orally6. We have investigated the possible use of water-in-oil-in-water (W/O/W) emulsions7 as a means of facilitating gastrointestinal absorption of normally non-absorbed water soluble biopolymers. Intraduodenal injection of such an emulsion containing insulin resulted in significant hypoglycaemic activity. These emulsions (also known as “mixed” or “multiple” emulsions) consist of oil droplets suspended in an aqueous phase, which, in turn, contain their own dispersed phase of finer water droplets. This internal aqueous phase presumably contains the therapeutic agent. Emulsions of this type are usually prepared in a stepwise manner beginning with the most finely dispersed phase. An aqueous solution of the therapeutic agent is incorporated into a continuous oil phase (using a suitable emulsifying agent). This results in a water-in-oil (W/O) emulsion which is then dispersed in a second aqueous phase (again with a suitable emulsifying agent) to give a W/O/W emulsion.

Development of the obese-hyperglycaemic syndrome in mice.

Abstract: Mice with the recessively inherited, obese-hyperglycaemic syndrome were studied at different stages of their development. Homozygous carriers of the syndrome already exhibited an excessive accumulation of fat resulting in overweight at an age of 26 days. A few days later the concentration of serum immunoreactive insulin was raised and then continuously increased until about 6 months of age. Subsequently there was a gradual decline to the levels observed in the lean litter mates. Serum glucose values above those of the lean controls were first observed at about 1 month of age. There was a subsequent increase of the blood sugar values until the mice were 3 months old, when the mean value was above 300 mg per 100 ml. The level then decreased until in 7 months old obese mice it did not differ from that in the lean litter mates. The concentration of serum free fatty acids of the obese mice was not significantly different from that of their lean litter mates; a decrease with age being observed for both types. In the old obese mice there was a fall also in the body weight to approximately normal levels. — Administration of insulin to the genetically future-obese mice displayed a higher insulin tolerance as reflected in a slower decrease of the blood sugar level at an age of 27 days. The ability of these mice to resist insulin-induced convulsions was tried as a method for an early identification of individual future-obese mice. It was, however, not possible to classify the mice completely into two genetically different groups at 23–25 days of age, although this test turned out to be fairly reliable. Glucose tolerance tests at the same early age were also found to be less useful. Only in 4 months old, obese-hyperglycaemic mice did an intraperitoneal glucose load result in a slower return of the blood sugar level to the pre-injection value. — The present findings indicate a triphasic development of the obese-hyperglycaemic syndrome. After an initial asymptomatic period lasting for the first 23–26 days of life, the various manifestations of the syndrome appear in the course of a few days. The subsequent period is characterized by increasing serum glucose and insulin concentrations and coincides approximately with the time of rapid gain in body weight. After the body growth ceases the abnormalities associated with the syndrome gradually disappear. The pattern of development of the syndrome is compatible with the view that diabetogenic factors are active during a limited period early in the life of the homozygous mice.

Cations and the secretion of insulin from rabbit pancreas in vitro

Abstract: 1 Insulin secretion from pieces of rabbit pancreas incubated in vitro was studied in media of different ionic compositions 2 Insulin secretion stimulated by glucose was abolished by removal of calcium from the incubation medium and inhibited by a twofold rise in the calcium concentration to 10·2 m-equiv/l Removal of magnesium from the medium did not affect glucose-stimulated secretion but a tenfold rise in the extracellular magnesium concentration to 24 m-equiv/l abolished secretion 3 The replacement of calcium by an equivalent amount of barium (5·1 m-equiv/l) stimulated insulin secretion Barium stimulation declined with time and was inhibited by the presence of calcium, 5·1 m-equiv/l, or abolished by the presence of magnesium, 24 m-equiv/l, in the incubation medium 4 The interactions of mono- and divalent cations on insulin secretion were studied by using ouabain or potassium as tools to raise intracellular sodium concentration and barium as a calcium analogue Ouabain and potassium were effective stimuli only in the presence of calcium, and barium only stimulated insulin secretion in the presence of sodium 5 The results of these experiments suggest that both calcium and sodium must act at the β cell membrane or enter the cell before insulin release can occur in response to a variety of stimuli

Early phase of insulin release

Abstract: The early phase of insulin release in the first five minutes after intravenous administration of glucose, glucagon , and glucose-plus-glucagon was investigated systematically in various clinical conditions. In normal subjects there is an immediate release of insulin after glucose, glucagon, and glucose-plus-glucagon infusions. The latter combination produced the highest insulin levels. Of a group of nonobese subjects with diabetic heritage , some had impaired early release of insulin, but0 their mean response did not differ significantly from the normal group. Investigation of nonobese potential diabetics (offspring of two diabetic parents) revealed that as a group average they had decreased insulin levels during the early phase of insulin release, even though intravenous glucose tolerance was normal. Four of ten subjects had a normal response. Nonobese, noninsulin-dependent diabetics had no insulin response to infused glucose, but when glucagon was added to glucose a significant and rapid insulin discharge was observed. However, the magnitude of this response was about half that seen in normal subjects after glucose-plusglucagon. Finally, the early phase of insulin release was studied in obese nondiabetic subjects who demonstrated an exaggerated insulin release to each stimulus. Again, glucose-plusglucagon was the most potent stimulator of insulin release. It is postulated that impairment in the early phase of insulin release may be the first detectable abnormality of insulin secretion in diabetes mellitus and that glucagon has the capability of restoring this toward normal.

Acute Insulin Withdrawal and the Regulation of Plasma Triglyceride Removal in Diabetic Subjects

Abstract: The effects of acute insulin deprivation on the enzyme lipoprotein lipase (LPL) and on triglyceride (TG) removal from plasma in man are unknown. To assess the role of insulin availability on TG removal, plasma TG concentration and postheparin lipolytic activity (PHLA)—an indirect means of quantitating LPL—were measured in seven insulin-dependent diabetics before and forty-eight hours after insulin withdrawal. The TG elevation (p

Juvenile Diabetes Mellitus, a Deficiency in Insulin

Abstract: The plasma insulin, growth hormone, nonesterified fatty acids and glucose responses to the oral ingestion of glucose, the intravenous administration of tolbutamide and the infusion of arginine were studied in fourteen newly diagnosed juvenile diabetic children. Fasting plasma insulin levels did not differ significantly between diabetic and normal children, although the mean fasting blood glucose level of the diabetic children was threefold greater than that of the normal subjects No detectable plasma insulin response was observed in the diabetic subjects during all three tests. Fasting plasma growth hormone levels and plasma growth hormone responses were similar in both normal and diabetic children. The fasting free fatty acid level of the diabetic children was significantly higher than in normal children, but fell during all three tests. With use of a variety of sensitive procedures, no antibodies to human insulin were demonstrable in the sera of newly diagnosed juvenile diabetics.