Raul A. Gutman

Circulating Proinsulin-like Material in Patients with Functioning Insulinomas

Abstract Because islet-cell tumors of the pancreas produce proinsulin-like material in vitro, the plasma of 11 patients with functioning insulinomas was studied to determine the immunoreactive insulin proportion contributed by circulating proinsulin-like material. The plasma of nine patients with insulinomas showed on gel filtration an increased proinsulin-like material (28 to 89 per cent) as compared to subjects of normal weight, those who were obese, and those with functional hypoglycemia (less than 20 per cent). Polyacrylamide-gel electrophoresis of serum showed material compatible with proinsulin, insulin and an intermediate component. Considering the data so far reported, any patient with hypoglycemia who shows an elevated percentage of proinsulin-like material should be suspected of having an insulinoma. In one patient, surgical removal of an islet-cell adenoma resulted in a fall of serum proinsulin-like material from 65 to 0 per cent. Determination of plasma proinsulin-like material may provide dia...

Studies on the biological activity of porcine proinsulin

The biological activity of purified porcine proinsulin was investigated in rats. In vivo studies revealed that proinsulin produced a hypoglycemic response similar to insulin but of lesser magnitude. Hypophysectomized and adrenalectomized animals proved to be more sensitive to proinsulin than normal. In vitro studies with rat hemidiaphragm were consistent with the in vivo findings. No competition with insulin action could be demonstrated. Experiments were carried out to determine whether proinsulin is converted to intermediate forms or insulin as a requisite to its biological activity. Labeled proinsulin injected in vivo or incubated in vitro remained intact by a variety of techniques (Sephadex column chromatography and polyacrylamide-gel electrophoresis). An inhibitory action of Kunitz pancreatic trypsin inhibitor on proinsulin action in vitro was confirmed. No clarification of this effect could be ascertained.

Glucose-induced insulin release patterns: Effect of starvation

SummaryContinuous glucose infusions over a 60 min period were carried out in 24 human subjects. A priming dose of 0.33 gm glucose/kg was followed by a constant infusion of 20 mg glucose/kg/min. The glucose-stimulated insulin release curves were biphasic (Phase I and II) in all subjects. The diabetics, compared with normal controls, showed decreased total insulin release with a greater decrement in phase I. Starvation of normal subjects for 48 h resulted in decreased insulin release, though Phases I and II were equivalently diminished. Rats were starved for 48 h and their pancreata studied in the isolated pancreas perfusion system. Following glucose stimuli, insulin release showed a pattern similar to that of diabetics, namely, decreased total insulin and a greater decrease in phase I than II. It is postulated that this period of starvation for a small animal was far more pronounced than that in man. The altered insulin secretory pattern in prolonged starvation is an additional manifestation of “starvation diabetes” and suggests the possibility of similar defects in starvation and diabetes.

Effect of Dehydration and Hyperosmolarity on Glucose, Free Fatty Acid and Ketone Body Metabolism in the Rat

The effect of water deprivation was studied in rats fasted twenty-four, forty-eight and seventy-two hours. Glucose tolerance was impaired and insulin levels were lower one hour after an intraperitoneal glucose load. Ketone bodies (KB) and free fatty acid (FFA) levels were significantly lower. FFA rise after epinephrine was reduced. Hypertonic mannitol (3 M) administered subcutaneously to fasted rats also resulted in glucose intolerance and decreased levels of FFA and KB. In vitro hyperosmolarity(50, 100 mOsm. per liter mannitol) reduced FFA release from rat epididymal fat pads and impaired pancreatic insulin response to glucose. No effect on ketone body production by perfused rat liver was found. It is postulated that the above metabolic effects of dehydration and hyperosmolarity may be involved in the pathogenesis of hyperosmolar nonketotic coma in patients.

Specific Biologic Effects of Intestinal Glucagon-Like Materials

It has been demonstrated that gastrointestinal extracts contain substances which react immunologically with antibodies prepared to pancreatic glucagon. These extracts have been termed intestinal GLI for glucagon-like immunoreactivity, or enteroglucagon. To determine whether GLI has specific biological effects, studies were designed using the criterion of effect with antiglucagon antibodies. These antibodies did not cross-react with either secretin or pancreozymin. Rat intestinal extracts were prepared and filtered on Sephadex G-50 columns eluted in 0.02 M ammonium carbonate buffer pH 8.8. Two peaks of GLI (I, II) were consistently found, and the in vitro effects of these peaks on two biological systems were tested: (a) immunoreactive insulin (IRI) release by rat pancreas pieces, and (b) free fatty acid (FFA) release and 3,5-cyclic adenosine monophosphate (cAMP) levels in adipose tissue. Both GLI peaks increased IRI release in the absence of glucose and also enhanced the glucose effects. Antiglucagon antibody suppressed only peak II GLI activity. Both peaks increased FFA release and cAMP levels in adipose tissue. Only peak II GLI activity was suppressed by antibody. These findings support a specific IRI-releasing and lipolytic action for Peak II GLI. Hypotheses are presented concerning the structure and possible physiologic role of peak II GLI.

Interaction of Various Stimulators and Inhibitors on Insulin Secretion in vitro

The effect of starvation on pancreatic insulin release was studied in vitro. A marked decrease in response to a glucose stimulus was present. Theophylline, tolbutamide, and dibutyrylcyclic AMP (DBcAMP

A method for electrophoretic characterization on polyacrylamide gel of circulating insulin immunoreactive substances

Abstract A method is described for determining the electrophoretic behavior of circulating insulin immunoreactive materials. A polyacrylamide immunoreactive pattern of serum can be determined on as little as 100 μU of insulin immunoreactive material. It is suggested that the utility of the method would be increased if it were coupled to a prior chromatographic separation of proinsulin like components from insulin by means of gel filtration. There is also considerable potential for use of this method as a preparative procedure for study of human circulating insulin components.