Jurgen Steinke

The Extractable Insulin Content of Pancreas from Fetuses and Infants of Diabetic and Control Mothers

The acid ethanol extractable insulin content of pancreases from thirty-seven infants and three early fetuses of diabetic and control mothers has been measured and their islet cell histology was studied. In general there was good agreement between these two parameters. Pancreatic insulin could be detected in one of two twelve-week old fetuses examined and in the pancreas of a fourteen-week old fetus of a diabetic mother. The remaining thirty-seven pancreases were obtained from fetuses of gestational age twenty weeks to term, nine of whom were offspring of diabetic mothers. The latter contained more insulin than the corresponding control group. The possible mechanisms are discussed; the hyperglycemic hypothesis is favored.

Early metabolic effects of human growth hormone.

Summary Human growth hormone, 8 mg, has been administered intravenously to 6 normal volunteers, and blood samples have been obtained before and from 10 to 240 minutes after injection of the hormone. The growth hormone preparation used exhibited a definite early insulin-like effect both in terms of blood glucose and plasma free fatty acid levels. This was not associated with a change in serum insulin-like activity, as measured with rat epididymal adipose tissue. Four hours after growth hormone had been given, there was a mild hyperglycemic effect, and a marked increase in plasma free fatty acids, together with a small but significant elevation in insulin-like activity of serum. These observations are interpreted as compatible with an intrinsic in vivo insulin-like activity of the growth hormone preparation used, which could be either a property of the growth hormone molecule itself, or represent the activity of unrelated substances present in the preparation.

Hyperinsulinemia and insulin resistance in genetically obese rats

Abstract Serum immunoreactive insulin levels (IRI) and insulin sensitivity were studied in lean, genetically obese “fatty” rats, and rats that became obese following hypothalamic lesions. Serum IRI was increased in obese “fatty” rats at 6 wk, 4 mo, and 11 mo of age. Similar increases were observed in hypothalamic lesioned (HTL) obese rats. Histologic changes in the appearance of islet tissue were described. Insulin sensitivity was studied in both “fatty” and HTL rats after a 19-hr fast. Genetic, but not regulatory, obesity was accompanied by insulin resistance. Possible reasons for this difference are discussed.

MEASUREMENT OF SMALL QUANTITIES OF INSULIN-LIKE ACTIVITY USING RAT ADIPOSE TISSUE. II. EVALUATION OF PERFORMANCE*

In the preceding paper (1), a biological assay method was proposed which utilized the increased production of CO2 from glucose in response to minute quantities of insulin by epididymal adipose tissue of rats. Since the quality of an assay method is best revealed by its performance over a period of time, the present report will present the results obtained during 25 months when this assay procedure was applied to insulin solutions and was tested on more complex material such as human blood serum. The quantitative evaluation of the data was carried out to a large extent independently from the actual performance of the assays, although consultations between the statistical and the biological teams occurred at irregular intervals of a few months.

Comparative effects of insulin on adipose tissue segments and isolated fat cells of rat and man.

In vitro metabolism of glucose-1-(14)C by adipose tissue into (14)CO(2) and total (14)C lipids in rat and man was compared employing both adipose tissue segments and isolated fat cells prepared from the same donor. In the rat, the basal glucose metabolism and response to insulin decreased with increasing body weight for both adipose tissue segments and isolated cells. Regardless of age, the isolated cells exhibited a persistently higher metabolic activity. Of the parameters selected, conversion to CO(2) was more pronounced than that to lipid.In contrast to the rat, in man adipose tissue segments were more active than isolated cells. In four subjects, the effect of 6, 50, and 400 muU/ml of insulin was analyzed on conversion of glucose-1-carbon to CO(2), long chain fatty acids, and glycerides by adipose tissue segments only. In 17 subjects, glucose oxidation and lipid synthesis by adipose tissue segments and isolated fat cells were measured and showed a definite response to physiological doses of crystalline pork insulin. There was, however, an age dependency, and consistent effects were obtained with 6 muU/ml in children and 50 muU/ml in adults. The responsiveness of human adipose tissue to exogenous insulin in concentrations comparable to those detected in blood reemphasizes the importance of adipose tissue as a major site for fatty acid synthesis.

Changes in the Islets of Langerhans in Cows Injected with Heterologous and Homologous Insulin

The histopathological findings in a group of cows injected with homologous or heterologous insulin in adjuvant are described. The essential features in the most severely affected cows (including two which received only bovine insulin) were lymphocytic infiltration of the islets of Langerhans with destruction of beta cells and fibrosis. The surviving beta cells showed signs of over-activity. The findings, which are regarded as having the characteristics of an “autoimmune” response, are discussed in relation to similar pathologic findings in human juvenile diabetes of recent onset.

Serum insulin measurements in children with idiopathic spontaneous hypoglycemia and in normal infants, children and adults.

THE role of insulin in the pathogenesis of idiopathic spontaneous hypoglycemia is obscure. This paper reports levels of serum immunoreactive insulin and levels of serum insulin-like activity in pat...

Acute ketotic-type diabetic syndrome in sand rats (Psammomys obesus) with special reference to the pancreas.

Twenty-seven sand rats obtained from the United Arab Republic during the summer of 1964 were studied. An acute ketotic-type diabetic syndrome was induced almost regularly and very acutely, when these animals were fed Purina laboratory chow instead of mixed fresh vegetables. The appearance of hyperglycemia was associated with increased serum insulin and decreased extractable pancreatic insulin. The subsequent fall in serum insulin levels is attributed to pancreatic exhaustion. Prior to the decrease in serum insulin, the beta cells reveal, by electron microscopy, degranulation, enhanced protein synthesis and glycogen infiltration.

The role of the pentose phosphate shunt in glucose induced insulin release: in vitro studies with 6-aminonicotinamide, methylene blue, NAD + , NADH, NADP + , NADPH and nicotinamide on isolated pancreatic rat islets.

Abstract The possible role of the pentose phosphate shunt in insulin release was investigated in vitro with collagenase isolated pancreatic islets of rats. Parameters measured were insulin released into the medium and measured by an immunoassay and formation of 14CO2 from glucose labeled either in the C-1 or C-6 position. The in vitro effect of the following substances was studied: 1. 1. 6-Aminonicotinamide, an antimetabolite in the synthesis of pyridine nucleotides. In islets of animals pretreated with 6-amino nicotinamide 6 h previously and in the presence of 3 mg/ml glucose in the incubation medium, 6-aminonicotinamide markedly reduced oxidation of [1-14C]glucose but did not affect that of glucose labeled in C-6. Concomitantly there was a marked decrease in insulin release. This action of 6-aminonicotinamide did not take place when it was added only to the incubation medium. Pretreatment with 6-aminonicotinamide did not change the insulin concentration of the islets, making it unlikely that it interfered with insulin synthesis. The effect of 6-aminonicotinamide is consistent with partial inhibition of the pentose shunt. 2. 2. Methylene blue: this agent was selected because it is known from studies with red blood cells that it will oxidize NADPH and thus stimulate activity of the pentose shunt. In concentrations of 0.5 and 2 μg/ml, methylene blue markedly stimulated oxidation of [1-14C]glucose but not that of C-6. Simultaneously there was a dose related decrease of insulin released. 3. 3. Pyridine nucleotides: in the absence of glucose only NADPH exhibited a significant effect of insulin release. If glucose (3 mg/ml) was present 1 or 10 mM of NAD+ or NADH exhibited a significant effect, NADP+ or NADPH were less effective. If the pentose shunt was blocked by pretreatment with 6-aminonicotinamide, all 4 pyridine nucleotides stimulated insulin release. Similarly there was an increase in oxidation of [1-14C]glucose, consitent with restimulation of the pentose shunt. 4. 4. Nicotinamide by itself exhibited a small effect; however, it was much less than the one produced by equimolar concentrations of the pyridine nucleotides. Conclusion: Restricted availability of NADPH either less production or by fast removal leads to a decrease in glucose-induced insulin release. Pyridine nucleotides will restimulate 6-aminonicotinamide blockade insulin release and glucose oxidation by the pentose shunt. Recently it has been proposed by others that the polyol pathway may play a key role in insulin release, our data are consistent with such a hypothesis. Furthermore they do support a major role of the pentose shunt in insulin release.

6-Aminonicotinamide (6-AN) as a Diabetogenic Agent: In Vitro and in Vivo Studies in the Rat

The effect of 6-aminonicotinamide (6-AN), an antimetabolite mainly of NADP synthesis, on insulin release, was studied. Adults rats were pretreated with 6-AN (35 mg./kg.); six hours later, the in vitro insulin response of isolated islets to glucose was significantly reduced from 561 ± 41 to 175 ± 22μU. of immunoreactive ingiilin (IRI) per five islets per ninety minutes incubation time. On the other hand, in vitro addition of NADP or NADPH (1 or 10 mM) to islets from pretreated rats, restored insulin release. In control islets, addition of NADP or NADPH showed little effect. It is unlikely that 6-AN affected insulin synthesis in vivo, as extractable insulin content of islets did not change (1.5 ± 0.1 vs. 1.4 ± 0.1 mU. IRI per single islet). In vivo studies with 6-AN pretreated rats showed marked hyperglycemia (344 ± 25 vs. 139 ± 11 mg./100 ml.) after a six-hour fast and still significant hyperglycemia following a twenty-four-hour fast (282 ± 33 vs. 94 ± 6). When challenged by intraperitoneal glucose, insulin failed to rise significantly in the 6-AN treated animals. It is thus possible to produce a new variant of experimental diabetes by interfering with NADPH metabolism within the beta cell. Our data suggest that glucose is involved in insulin release as a generator of NADPH via the pentose-phosphate shunt.