Influence of heparin-plasma, EDTA-plasma, and serum on the determination of insulin with three different radioimmunoassays

Immunoreactive insulin stability in horses at risk of insulin dysregulation

Background

Diseases associated with insulin dysregulation (ID), such as equine metabolic syndrome and pituitary pars intermedia dysfunction, are of interest to practitioners because of their association with laminitis. Accurate insulin concentration assessment is critical in diagnosing and managing these diseases.

Hypothesis/Objectives

To determine the effect of time, temperature, and collection tube type on insulin concentrations in horses at risk of ID.

Animals

Eight adult horses with body condition score >6/9.

Methods

In this prospective study, subjects underwent an infeed oral glucose test 2 hours before blood collection. Blood samples were divided into ethylenediaminetetraacetic acid, heparinized, or serum tubes and stored at 4 or 20°C. Tubes were centrifuged and analyzed for insulin by a chemiluminescent assay over 8 days. Changes in insulin concentrations were compared with a linear mixed effects model.

Results

An overall effect of time, tube type and temperature was identified (P = .01, P = 0.001, and P = 0.001, respectively). Serum and heparinized samples had similar concentrations for 3 days at 20°C and 8 days at 4°C; however, after 3 days at 20°C, heparinized samples had significantly higher insulin concentrations (P = .004, P = .03, and P = .03 on consecutive days). Ethylenediaminetetraacetic acid samples had significantly lower insulin concentrations regardless of time and temperature (P = .001 for all comparisons).

Conclusions and Clinical Importance

These results suggest an ideal protocol to determine insulin concentrations involves using serum or heparinized samples with analysis occurring within 3 days at 20°C or 8 days at 4°C.

A new, microalgal DHA- and EPA-containing oil lowers triacylglycerols in adults with mild-to-moderate hypertriglyceridemia

In this double-blind, parallel trial, 93 healthy adults with hypertriglyceridemia (triacylglycerols [TAG] 150-499 mg/dL) were randomized to receive either a nutritional oil derived from marine algae (DHA-O; 2.4 g/day docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA] in a 2.7:1 ratio), fish oil (FO; 2.0 g/day DHA and EPA in a 0.7:1 ratio), or a corn oil/soy oil control as 4-1g softgel capsules/day with meals for 14 weeks; and were instructed to maintain their habitual diet. Percent changes from baseline for DHA-O, FO, and control, respectively, were TAG (-18.9, -22.9, 3.5; p<0.001 DHA-O and FO vs. control), low-density lipoprotein cholesterol (4.6, 6.8, -0.6; p<0.05 DHA-O and FO vs. control), and high-density lipoprotein cholesterol (4.3, 6.9, 0.6; p<0.05 FO vs. control). This study demonstrated that ingestion of microalgal DHA-O providing 2.4 g/day DHA+EPA lowered TAG levels to a degree that was not different from that of a standard fish oil product, and that was significantly more than for a corn oil/soy oil control.

The kinin B1 receptor antagonist SSR240612 reverses tactile and cold allodynia in an experimental rat model of insulin resistance

BACKGROUND AND PURPOSE

Diabetes causes sensory polyneuropathy with associated pain in the form of tactile allodynia and thermal hyperalgesia which are often intractable and resistant to current therapy. This study tested the beneficial effects of the non-peptide and orally active kinin B(1) receptor antagonist SSR240612 against tactile and cold allodynia in a rat model of insulin resistance.

EXPERIMENTAL APPROACH

Rats were fed with 10% D-glucose for 12 weeks and effects of orally administered SSR240612 (0.3-30 mg kg(-1)) were determined on the development of tactile and cold allodynia. Possible interference of SSR240612 with vascular oxidative stress and pancreatic function was also addressed.

KEY RESULTS

Glucose-fed rats exhibited tactile and cold allodynia, increases in systolic blood pressure and higher plasma levels of insulin and glucose, at 12 weeks. SSR240612 blocked tactile and cold allodynia at 3 h (ID(50)=5.5 and 7.1 mg kg(-1), respectively) in glucose-fed rats but had no effect in control rats. The antagonist (10 mg kg(-1)) had no effect on plasma glucose and insulin, insulin resistance (HOMA index) and aortic superoxide anion production in glucose-fed rats.

CONCLUSIONS AND IMPLICATIONS

We provide the first evidence that the B(1) receptors are involved in allodynia in an experimental rat model of insulin resistance. Allodynia was alleviated by SSR240612 most likely through a direct inhibition of B(1) receptors affecting spinal cord and/or sensory nerve excitation. Thus, orally active non-peptide B(1) receptor antagonists should have clinical therapeutic potential in the treatment of sensory polyneuropathy.

Dietary amino acids fed in free form and as protein components do not differently affect postprandial plasma insulin, glucagon, growth hormone and corticosterone responses in rats

This study examined, whether the postprandial fate of dietary amino acids from different amino acid sources is regulated by the responses of insulin, glucagon, corticosterone and growth hormone (GH). Male Wistar rats were cannulated in the vena jugularis and assigned to dietary groups. The diets contained 21% casein or the same amino acids in free form. In the free amino acid diets, methionine level was varied between the groups. The feed was supplied in two distinct meals. In previous experiments it was established that oxidative amino acid losses of the free amino acid diets and protein diets were different. After 3 weeks on those diets, it appeared that the differences in postprandial oxidative losses had been diminished. GH was measured every 12 min, from 144 min before the start of the experimental meal over the following 144 min. Insulin and corticosterone were measured six times from the start of the meal until 270 min after the meal. No differences have been observed between the hormonal responses to both meals at day 5 and at day 26. In conclusion, it has been found that the differences in the oxidative losses between protein and free amino acid meals are not mediated by the combined action of the insulin, glucagon, corticosterone and GH. Postprandial catabolism of amino acids is most probably regulated by substrate induction.

Pig-to-nonhuman primate islet xenotransplantation: a review of current problems

Islet allotransplantation has been shown to have potential as a treatment for type 1 diabetic patients. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited number of islets. This comprehensive review focuses on experience obtained in pig-to-nonhuman primate models, particularly with regard to the different types of islets (fetal, neonatal, adult) and isolation procedures used, and the methods to determine islet viability. The advantages and disadvantages of the methods to induce diabetes (pancreatectomy, streptozotocin) are discussed. Experience in pig-to-nonhuman primate islet transplantation studies is reviewed, including discussion of the possible mechanisms of rejection and the immunosuppressive regimens used. The research carried out to date has led to workable animal models to study islet xenotransplantation, but several questions regarding methodology remain unanswered, and details of these practicalities require to be adequately addressed. The encouraging porcine islet survival reported recently provides an indicator for future immunosuppressive regimens.

The effect of secretin on serum group I pepsinogens (PG I) in man

Six healthy young males were studied with an intravenous infusion of secretin, 2 CU/kg body weight and hour in saline, or with saline alone for 3 h on two separate days. Blood was drawn before and at regular intervals during the infusions, and serum PG I was determined by radioimmunoassay. After an initial decline on both days, serum PG I rose significantly during the secretin infusion. The initial fall in serum PG I was probably not caused by heparin used to keep the indwelling catheter open, since a similar fall was also observed in another six subjects in whom saline was used to keep the catheter open. Moreover, heparin added to the serum did not affect the measurement of PG I.

Fasting metabolism in infants. I. Effect of severe undernutrition on energy and protein utilization

Fasting energy metabolism was studied in infants to determine the rates of utilization of endogenous carbohydrate, fat, and protein in relation to length of fasting, glucose homeostasis, other circulating energy substrates and hormones, and severe depletion of energy reserves due to prior malnutrition. Five subjects about 1 yr of age were each studied before and after restoration of their energy reserves. Following 3 days of a standard maintenance intake of energy and protein, the subjects were fasted until glycogen oxidation became negligible. Total energy utilization, determined by hourly oxygen consumption, did not diminish as a result of fasting but was significantly less when malnourished than when recovered, 66 versus 79 kcal/kg/day. In all cases the major energy source shifted from oxidation of dietary carbohydrate and glycogen to oxidation of fat, determined from the respiratory quotient, until the oxidation of glycogen became negligible and fat provided 94% of energy in the malnourished subjects after 21 hr and 92% in the recovered subjects after 27 hr. Utilization of protein, determined from urinary nitrogen excretion, remained very low in the malnourished infants accounting for a maximum of 4% of energy, 103 mg N/kg/day, whereas after recovery, protein utilization doubled as a result of fasting, finally accounting for 7% of energy, 226 mg N/kg/day (p less than 0.005). Urea accounted for 60% of total urinary N in both groups and plasma urea increased correspondingly in the recovered but not in the malnourished subjects. Plasma glucose decreased to about 40 mg/100 ml in both groups as glycogen oxidation diminished. The maximum amount of glucose that could have been derived from dietary carbohydrate, glycogen, glycerol, and amino acids decreased over this time from about 6 to 1 mg/kg/min. Alanine declined in relation to glucose concentration and was not different in the two groups in spite of the difference in urea production. Glycerol free fatty acids, beta-hydroxybutyrate, and acetoacetate increased in both groups, but the latter three of these remained significantly less in the malnourished group. Insulin decreased rapidly and remained equally low in both groups. Urinary epinephrine increased in both groups and cortisol was elevated after fasting, while growth hormone did not increase significantly. It is concluded that fasting infants complete the transition from dietary carbohydrate to endogenous fat as the major energy source much faster than do adults, proportionate to relatively greater energy utilization. Severe wasting did not prevent energy homeostasis in spite of greatly depleted body fat. Oxidation of fat continued to provide virtually all of the fasting energy requirements, although ketosis was relatively less. Utilization of endogenous protein also increased as a result of fasting but, by contrast, provided only a very small fraction of total energy, and this was substantially diminished as a result of wasting, similar to what has been found in starved adults...

Effects of treatment with pyruvate and tromethamine in experimental myocardial ischemia

Failure of glycolysis to increase sufficiently to supply optimal levels of energy production in ischemic heart muscle is due in part to the cummulative restrainst of acidosis on rate-limiting enzymes, particularly glyceraldehyde-3-phosphate dehydrogenase. In an effort to modify this inhibition and salvage jeopardized myocardium, treatment with excess levels of pyruvate and tromethamine (Tris), designed to buffer intracellular hydrogen ion accumulations and improve the oxidation-reduction ratio, NAD+/NADH, was tested in 59 swine hearts in two separate preparations of global and regional ischemia. Global ischemia, per se, caused hemodynamic deterioration and shortened survival time (44.3 +/- 3.1 minutes). Myocardial oxygen consumption, fatty acid oxidation, and glucose uptake were all significantly (P less than 0.001) reduced as were estimates of glycolysis and tissue stores of creatine phosphate and ATP (P less than 0.01). Although treatment with Tris alone was inconclusive, administrations of pyruvate (40-50 mM) buffered with Tris (added directly into the coronary perfusate) effected an improvement in mechanical function and a significant prolongation in survival time (56.9 +/- 2.6 minutes. P less than 0.01). Glycogenolysis was enhanced and levels of key glycolytic intermediates were reduced, suggesting an acceleration of glycolytic flux. Excess levels of pyruvate (1.52 +/- 0.48 mumol/ml of coronary perfusate) provided added substrate for oxidation and led to a greater than 5-fold incrase in rates of pyruvate decarboxylation as compared to untreated ischemic hearts...