Immunoreactive Insulin Activity Research Articles

Optimal dose and duration of glucose administration during fasting period preceding surgery in rabbits.

We examined preoperative glucose administration to establish what dose and cutoff point were optimal for suppression of lipolysis and prevention of hypo- or hyperglycemia. Rabbits were preoperatively fasted and simultaneously received glucose at a constant rate of 0, 0.1, 0.2, 0.3, or 0.4 g.kg(-1).h(-1) in fluid infusion for 3 h. Plasma glucose, immunoreactive insulin activity, nonesterified fatty acids, and ketone bodies were measured 0, 1.5, 3 and 4 h after the start of infusion, and hepatic glycogen content was assessed 1 h after cessation of infusion. Fluid infusion without glucose decreased plasma glucose. Glucose administration at more than 0.2 g.kg(-1).h(-1) caused hyperglycemia (>200 mg.dl(-1)) in the infusion period; the differences were significant compared with the value at zero time or in the 0 g.kg(-1).h(-1) group (P < 0.01). The highest dose also raised plasma immunoreactive insulin activity, which was significantly higher than in the 0 g.kg(-1).h(-1) group (P < 0.01) at the midpoint of the infusion period. Plasma nonesterified fatty acids increased in all groups. The changes were, however, significantly reduced in both the 0.3 and 0.4 g.kg(-1).h(-1) groups (P < 0.05 and P < 0.01, respectively) by the end of infusion. All these effects of glucose supply, including suppression of lipolysis, disappeared regardless of dose within 1 h after the cessation of infusion. These results suggest that the optimal dose for preoperative glucose infusion, in order to preserve carbohydrate or fat metabolism, is 0.1-0.2 or 0.3 g.kg(-1).h(-1), respectively, and indicate that administration should not be discontinued until the start of surgery.

Induction of insulin release in fibroblasts transfected with genomic rat islet DNA

L cells (tk −) were cotransfected with total genomic rat islet DNA and a plasmid containing thymidine kinase gene (ptk). Transfectants were tested for their ability to release insulin into the medium. At least 10% of the colonies contained immunoreactive insulin (IRI) during the initial two weeks. The insulin secreted competed linearly with rat insulin in RIA, the majority of the insulin antigenicity comigrating with rat insulin on G-50 Sephadex chromatography. With continuing propagation the IRI activity diminished; however 3 selected cultures demonstrated increased secretion of IRI following stimulation with glucose. These findings indicate that glucose-induced insulin secretion can be obtained in non-beta cells; however the frequency of success was below one stable transfection for every 5×10 8 Ltk − cells exposed to the transfection procedure.

Effect of estrogens on blood sugar, serum insulin and serum free fatty acids, and pancreas cytology in female dogs.

We analyzed the changes in blood sugar (BS), serum immunoreactive insulin (IRI), circulating free fatty acids (FFA) and pancreatic cytology caused by estrogenization at low pharmacological dosage in female dogs. Vehicle-injected and untreated controls (anestrus) were studied as well. Neither mean basal BS nor basal serum IRI was modified by the treatments, while the mean basal serum FFA value was raised. Glucose tolerance was not modified by the estrogens while glucose y-mean was significantly raised. Hyperglycemia was higher for a longer time in estrogenized animals compared to both controls, while the profiles of hyperinsulinemia coincided. In the estrogen-treated bitches, the pancreatic B-cells contained scarse brown-stained granules near their vascular pole, as shown by an immunochemical method. In the peripheral part of the pancreas, near the acini, some solitary, poorly beta-granulated B-cells were present. During the IVGTT, serum FFA reached lower values for a longer time in the estrogenized bitches as compared to those found in both control groups. Insulin-induced hypoglycemia in the estrogenized animals coincided with the one evoked in the vehicle controls; in the semilog relationship of serum IRI and time, y-mean was lower than that observed in oil-injected controls, and insulin space was larger. The serum FFA levels of these estrogenized bitches, very high in the basal conditions, did not respond to insulin administration, and were above those found in untreated controls and also in vehicle-injected controls just at the beginning of the test. These results are discussed. We came to the conclusion that estrogenization causes some glucose intolerance in bitches while insulin sensitivity remains normal in the IVITT as studied measuring BS. The glucose intolerance is thought to be related to a reduction in glucose space and occurs despite the normality of the serum IRI response. The pancreas must have an intense secretory response in vivo as as to maintain normal IRI activity despite degranulation of the islets of Langerhans and poor islet hypertrophy and neoformation. The serum FFA changes are thought to contribute towards the tendency to adiposity in these animals.

Attempts to prepare 'insulin-free plasma' from human subjects: effects of serial dilution and insulin recovery studies on immunoreactive insulin activity of partially insulin-free plasma.

The reason for attempts to prepare insulin-free plasma from human plasma is discussed. Binding agent, employed to prepare insulin-free plasma, had a capacity to bind 40% of insulin in the system. Insulin recovery from the filtrate of human standard insulin-binding agent reaction was 60%. Human plasma incubated with binding agent gave a filtrate--partially insulin-free plasma (PIFP)--which contained significantly higher amounts of insulin compared to calculated values. Insulin in PIFP was not augmented by serial dilution. Human standard insulin added to PIFP was recovered in full and the mixture was not dilution augmentable. Incubation of human plasma--human standard insulin (106 microunits/ml) mixture with binding agent gave a PIFP which had 60% of total insulin in the mixture. Dialysis did not alter the immunoreactive insulin activity of plasma. Dialysed samples showed augmentation of insulin activity on serial dilution. These observations strongly suggest the presence of a high molecular-weight, insulin-like inhibitory component in human plasma.

Metabolic changes after jejuno-ileal bypass for obesity.

Metabolic parameters were studied in 6 patients before and for 18 months after jejunoileal bypass for obesity. The postoperative changes in plasma concentration of amino acids were characterized by a decrease in essential amino acids, while the non-essential amino acids were unchanged or elevated, indicating a state of protein-caloric malnutrition. The pattern of fatty acids in serum the first year after operation: an unchanged sum of unsaturated and saturated fatty acids accompanied by a significant fall in linoleic acid and a corresponding increase in oleic acid, showed that even during this period the patients were in a state of essential fatty acid deficiency. The oral glucose tolerance test and the levels of serum immunoreactive insulin activity indicated a general improvement in glucose tolerance and a normalization of preoperative hyperinsulinism. A 40-50% reduction was found both in serum triglycerides and cholesterol levels. Serum iron was reduced by approximately 30%, whereas TIBC levels remained unchanged. The Schilling test showed a significant fall in vitamin B12 absorption postoperatively with subnormal values at 6 and 12 months. Vitamin B12 in serum dropped, but remained within the normal range, suggesting that the preservation of 25 cm of distal ileum is sufficient to secure adequate absorption of vitamin B12. Folic acid levels in serum fell after the bypass, demanding supplementation in 5 of the 6 patients at 6 months postoperatively.

The mechanism of insulin secretion after oral glucose administration V. Portal venous IRI concentration in dogs after ingestion of glucose.

Concentrations of immunoreactive insulin activity and of blood glucose were measured in portal and peripheral venous blood in six conscious dogs after oral administration of 1.0 g/kg glucose. Portal venous samples were obtained either by chronic catheterization or by direct puncture of the portal vein through a London-cannula. Portal venous IRI was already significantly increased 5 min after the onset of the stimulus. Peripheral venous IRI pattern reflected this early increase, but the peripheral venous blood glucose level was unchanged. The results indicate that the early peripheral venous IRI increase reflects a pancreatic insulin secretory reflex.

Effect of dilution on immunoreactive insulin activity of human plasma.

1. Plasma from normal fasting subjects showed significant augmentation of immunoreactive insulin activity on serial dilution. This augmentation effect was not observed in samples obtained after glucose loading or in samples mixed with high concentrations of human standard insulin. 2. Low concentrations of human standard insulin (13 and 25 μU/ml) added to undiluted plasma were fully recovered. Serial dilution of such plasma-insulin mixtures showed augmentation of immunoreactive insulin activity. 3. High concentration of human standard insulin (65.5 μU/ml) added to undiluted plasma was fully recoverable. No augmentation of immunoreactive insulin activity was observed on dilution of such plasma-insulin mixtures. 4. Altering the pH of plasma from pH 7.4 to pH 3.0 did not reveal augmentation. 5. Human standard insulin curve was not significantly altered by the presence of porcine proinsulin. Immunoreactive insulin activity of human plasma mixed with porcine proinsulin did not change, while the same activity was augmented on serial dilution. 6. The results presented here suggest that: a. the augmentation effect is due to the presence of a component of inhibitory nature, b. the 'component' present in undiluted plasma specifically influences the first step, i.e. antigen-antibody complex formation, c. the influence of the 'component' is dependent on the level of immunoreactive insulin and d. this pH dependent 'component' of inhibitory nature does not appear to be proinsulin-like material.

The effect of meal feeding and of sham-feeding on insulin secretion in dogs.

After feeding intact conscious dogs 1000 g mashed meat, peripheral venous immunoreactive insulin activity (IRI) increases before any enhancement of amino nitrogen concentration. This course of IRI is paralleled by a decrease of free fatty acids. Meal feeding in dogs, whose pancreatic juice is completely diverted from the gut by a fistula, is followed by a similar IRI increase without a distinct enhancement of amino nitrogen. In oesophagus fistula dogs, sham-feeding meat in 9 out of 15 experiments results in a considerable early IRI increase which is correlated with a small but a significant decrease of blood glucose and free fatty acid concentrations. In these tests there was no amino nitrogen alteration either.

Hypoglycemia caused by an intrathoracic tumour.

Abstract. A patient with a large intrathoracic tumour associated with hypoglycemic attacks and whose fasting glucose levels were frequently below 30 mg/100 ml is described. The immunoreactive insulin (IRI) level during the hypoglycemic attacks and fasting was less than 5 μU/ml. The oral glucose tolerance test was normal. Glucagon gave a subnormal increase in blood glucose and no increase in serum IRI levels. Diazoxide did not reduce the frequency of attacks. The hypoglycemic attacks subsided after removal of a 5 kg cell‐rich mesenchymal tumour, which was probably a neurofibroma. The IRI concentration in the primary tumour extract was 0.05% of that found in extract from normal pancreatic tissue, and only 0.0005–0.1 % of that reported for insulinomas. On Sephadex‐LH gel filtration the low IRI activity was not eluted as insulin or proinsulin. All findings support the view that the hypoglycemia was not caused by insulin production by the tumour. Other possible causes are discussed.

Changes in fat and carbohydrate metabolism caused by moderate exercise in patients with acromegaly.

1. Seven patients with acromegaly and nine controls were studied before, during and after 30 min of moderate steady exercise on a bicycle ergometer. Venous blood samples were taken for estimation of growth hormone (HGH), immunoreactive insulin (IRI), pyruvate, lactate, glucose, free fatty acids (FFA), glycerol and ketone bodies. 2. Exercise caused a rise in HGH concentrations in the acromegalic patients, despite their pituitary tumour, and also in control subjects. Concentrations of IRI fell during exercise in control subjects, but rose in the acromegalic patients. 3. Concentrations of glycerol, FFA and ketone bodies rose rapidly to a maximum during exercise in the acromegalics and appeared to be suppressed before the end of exercise: there was no increase in the concentration of ketone bodies after exercise. In control subjects there was a gradual increase in glycerol and FFA concentrations towards the end of exercise, but no change in ketone bodies occurred until the post-exercise period, when ketone-body concentrations rose. 4. We conclude that exercise causes remarkable differences in metabolite concentrations in the blood of acromegalic patients compared with controls, with the concentration of fat metabolites reaching a maximum, then decreasing during the period of constant exercise. There was also elevation, instead of the normal fall, of plasma IRI activity and it is suggested that the decreased concentration of fat metabolites occurred because of the change of insulin concentration. It is further suggested that in acromegaly insulin retains its effect on re-esterification of fat in spite of resistance to its effects on carbohydrate metabolism.

Serum insulin levels in non-ketotic hyperosmotic diabetes mellitus.

AbstractTwo patients in the non-ketotic hyperglycemic diabetic state are reported. Blood glucose levels of 1982 mg % and 660 mg % and concurrent serum immunoreactive insulin activities of five μu/ml and 12 μU/mi were found. It is postulated that these abnormally low insulin activities were the resul