Studies of a simplified plasma insulin immunoassaay using cellulose powder

A modified plasma radioimmunoassay has been developed that uses a cellulose slurry to separate bound from free insulin. This material, which is commercially available, shelf stable, and simple to prepare, makes it possible to run the entire method in test tubes and to use a low specific activity insulin. Details concerning conditions and materials that determined sensitivity, accuracy, and precision are reported. The method is sensitive to about 10 μU/ml. of plasma and has a reproducibility of approximately ± 15 per cent. This method is proposed for use by those who desire to measure rises in plasma insulin by a simple, rapid and reasonably accurate technic.

Role of the kidney in the disposal of radioiodinated and nonradioiodinated insulin in dogs

Insulin concentration in each sample of dog urine, carotid artery plasma, or renal vein plasma was estimated following the infusion of bovine insulin-I-125, unlabeled bovine insulin, or glucose.

Insulin was estimated by immunoassay and by TCA insoluble radioactivity. Whenever insulin-I-125 and unlabeled insulin were infused together both methods were used on each sample.

In agreement with the conclusions of others, who have used less direct technics, it was found that the use of plasma TCA insoluble radioactivity to determine radio-insulin degradation in vivo results in an underestimate of insulin removal, and hence an overestimate of insulin half life. This finding was shown to apply not only to the whole animal but also to the kidney. All forms of insulin were removed by the kidney but the radioactive estimate of kidney insulin removal was less than that by immunoassay.

Data from experiments in which radioactive insulin was bound to guinea pig anti-insulin serum prior to infusion and from experiments in which ureteral ligation was performed prior to infusion indicated that the kidney removed insulin primarily by glomerular filtration but that direct absorption also played a role.

The effect of long-term streptozotocin-induced diabetes on the hepatotoxicity of bromobenzene and carbon tetrachloride and hepatic biotransformation in rats

To exclude the possibility that changes in hepatotoxicity and biotransformation were induced by diabetogen administration, the influence of long-lasting experimental insulin-dependent diabetes on the activities of benzphetamine demethylase, styrene oxide hydrolase, and UDP-glucuronosyl-transferases toward 1-naphthol, diethylstilbestrol, estrone and testosterone, and glutathione S-transferases toward 1-chloro-2,4-dinitrobenzene, ethacrynic acid, and sulfobromophthalein was studied. Adult male Sprague-Dawley rats injected with 45 mg streptozotocin/kg rapidly developed the classical symptoms of diabetes which persisted throughout the 90-day test period. Ketonemia was detectable at 6 but not at either 35 or 90 days after streptozotocin administration. After acute challenge with bromobenzene or carbon tetrachloride (CCl4), aspartate and alanine aminotransferase activities in rats diabetic for 35 and 90 days were markedly higher than those in normal rats, suggesting that diabetes potentiated the hepatotoxicity of these chemicals. Administration of 25 microliters CCl4/kg, ip, to diabetic rats decreased enzyme activities toward benzphetamine, sulfobromophthalein, 1-chloro-2,4-dinitrobenzene, and 1-naphthol. In normal rats, a dose of 400 microliters CCl4/kg, ip, was required to cause similar changes in enzyme activities. Bromobenzene (500 microliters/kg, ip) elicited opposing responses in diabetic and normal rats in N-demethylase activity, in UDP-glucuronosyltransferase activity toward 1-naphthol, estrone, and testosterone, and in glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene. Total cytochrome P450 concentrations were reduced by both induction of diabetes and hepatotoxicant challenge. Thus, chronic uncontrolled diabetes alters the response of hepatic xenobiotic biotransformation enzymes in a non-uniform, substrate-dependent manner, independent of initial diabetogen effects. The role of cytochrome P450j in potentiating CCl4 toxicity is discussed.

Possible role of hydrazine group in hypoglycemia associated with the use of certain monoamine-oxidase inhibitors (MAOI's)

It has been reported that some patients treated chronically with certain monoamine-oxidase inhibitors (MAOI's) exhibit as a complication hypoglycemia, or potentiation of insulin or sulfonylurea induced hypoglycemia. This effect has been attributed to interference by the MAOI with the hyperglycemic role of the sympathoadrenal system in glucose homeostasis, possibly through replacement of endogenous stored catecholamines by impotent “false transmitter.” These hypotheses lead to certain expectations, none of which were realized in the present experiments. Instead, evidence was obtained that it is the hydrazine group present in certain MAOI's, rather than their MAOI activity, to which hypoglycemic action should be attributed. Hydrazine and the hydrazine MAOI, phenelzine, induced similar decreases in plasma glucose and insulin levels of overnight fasted rats; phenelzine induced increases in plasma FFA levels. The nonhydrazine MAOI, pargyline, induced marked increases in plasma glucose levels.

Steroid priming of the luteinizing hormone response to luteinizing hormone releasing hormone

Perifusion experiments were performed to study the stimulatory effects of luteinizing hormone releasing hormone (LH-RH) on the release of LH from anterior pituitary tissue. Exposure of pituitary tissue from normal male rats to LH-RH (5 ng/ml for 5 min) induced a small release of LH; in tissue from ovariectomized rats receiving no pretreatment, the release was more than three times greater and in tissue from gonadectomized male or female rats pretreated with oestradiol benzoate and progesterone, the release was six times greater than that observed in normal rats. Further exposure of pituitary tissue from gonadectomized steroid-pretreated male and female rats to LH-RH (5 ng/ml) induced an increase in the level of LH even greater than that seen after the initial exposure (priming action of LH-RH); in tissue from ovariectomized rats receiving no pretreatment, less LH was released than after the first exposure to LH-RH and in tissue from normal male rats the response was unchanged.

Effect of volatile anesthetics on the hepatic UDP-glucuronic acid pathway in mice

Large, rapid decreases in hepatic UDP-glucuronic acid concentrations occur in rats following exposure to myriad chemicals. In fact, 80% reductions in UDP-glucuronic acid occur within minutes after exposure to inhalation anesthetics. The present study was designed to determine whether this decrease in hepatic UDP-glucuronic acid may be due to (a) a decrease in the precursor UDP-glucose; (b) decreased activity of UDP-glucose dehydrogenase, which oxidizes UDP-glucose to UDP-glucuronic acid; (c) increased activity of UDP-glucuronosyltransferases; or (d) increased activity of nucleotide pryophosphatase, which degrades UDP-glucuronic acid to glucuronic acid-1-phosphate. Exposure to halothane, isoflurane and sevoflurane decreased UDP-glucuronic acid concentrations by 40-52% as compared to that in unanesthetized control mice. No sex-dependent or anesthetic-induced effects of UDP-glucose levels and the activities of UDP-glucose dehydrogenase and UDP-glucuronosyltransferase were observed. Nucleotide pyrophosphatase activity was increased by 47-65% in female mice after inhalation of halothane, isoflurane and sevoflurane. The apparent Vmax for hydrolysis of 4-nitrophenol thymidine 5'-monophosphate ester by nucleotide pyrophosphatase was increased by 56-80% in female mice, whereas the apparent Km was unchanged. These alterations in nucleotide pyrophosphate kinetics may be responsible, in part, for the marked decrease of hepatic UDP-glucuronic acid concentrations by the volatile anesthetics.

On insulin I-131 metabolism in mice. Modifying effects of anti-insulin serum and of total insulin dosage

Estimations have been made on abilities of certain tissues of mice injected intravenously with insulin I-131 to concentrate and degrade this compound; change of I-131 from TCA insoluble to TCA soluble form has been used as measure of degradation. Insulin I-131, estimated as TCA insoluble I-131, was concentrated by liver and especially by kidney; formation of TCA soluble I-131 occurred most rapidly in liver. With insulin I-131 held constant but total insulin progressively increased, concentration ratios for TCA insoluble I-131 progressively increased in kidney, and decreased in other tissues. In all tissues, conversion of I-131 from TCA insoluble to TCA soluble form decreased progressively with increase in total insulin. Prior mixing of insulin I-131 with excess guinea pig anti-insulin serum (AIS) resulted in loss of tissue abilities to convert the I-131 into TCA soluble form, and in loss of abilities of all tissues other than liver to concentrate this TCA insoluble I-131.

Tris (hydroxymethyl) aminomethane (THAM) induced stimulation of insulin release by islets of Langerhans previously isolated from rat pancreas

Islets isolated from rat pancreas were studied in regard to release of immunoreactive insulin (IRI) as influenced by changes in glucose concentration and pH and type of buffer in the incubation media. The pH of the media was varied from 7.4 to 9.0. For phosphate and bicarbonate buffered media, change in pH did not result in significant change in IRI release rates. For media containing the pH buffer and chelating compound THAM (Tris [hydroxymethyl] aminomethane), IRI release increased significantly with increase in either THAM concentration or pH. Since increase in pH results in increase in that fraction of THAM which is in the unionized, therefore presumably more readily penetrating form, it is postulated that THAM molecules penetrate and act at intracellular loci to induce insulin release, possibly by chelating Zn complexed with insulin in beta cell granules.

On the rapidity with which LRH induces release of LH and FSH from perifused anterior pituitary tissues of the rat

In a series of perifusion (superfusion) experiments, data were obtained which indicated that LRH and K+, when effective, induced increase in LH and/or FSH release within about one minute after arriving in the vicinity of the test rat pituitary tissues. Hormone release stimulating effects of LRH or high K+ continued for some time after washout of test agent. To secure these data perifusion flow was set at 2.5 or more ml/min., each test solution was pulsed for two minutes only, effluent samples were collected at 15 second intervals shortly before, during and after each pulse, and both mixing and dead space time were minimized by introducing each new test solution directly in front of the tissue chamber, via a 4-way or 5-way pulse control stopcock through which two streams of perifusion fluid (Control and Test) passed continually. LH and FSH in effluent samples were estimated by radioimmunoassay.

Estimation of insulin secretion using extracts of plasma from mice injected with anti-insulin serum: effects of arginine, glucose and anti-insulin serum

Anti-insulin serum (AIS) injected intravenously into adult male mice was allowed to complex endogenous plasma insulin for a fixed time before blood samples were taken. In each plasma sample, insulin was separated from antibody using acid alcohol and the free insulin was estimated by radioimmunoassay. We consider AIS to be most useful for the estimations of in-vivo insulin secretion rates over the period 0.5-5 min after its injection. The lower limit is governed by the time required for mixing and complexing of endogenous insulin. The use of a short upper limit is because antibody complexed with antigen leaves plasma more rapidly than does free antibody, carrying antigen with it. Increases in insulin per ml plasma were appreciably greater in mice injected with glucose or L-arginine plus AIS than in mice injected with glucose or L-arginine only. Hence more realistic values for in-vivo insulin secretion rates may be obtained by the use of AIS to retain most insulin in plasma than by estimation of plasma insulin levels.