Development of a highly sensitive and selective microplate chemiluminescence enzyme immunoassay for the determination of free thyroxine in human serum.

A microplate chemiluminescence enzyme immunoassay (CLEIA) with high sensitivity, selectivity and reproducibility was developed for the determination of free thyroxine (FT4) in human serum. A competitive assay has been utilized with horseradish peroxidase (HRP) labeled thyroxine analog in the chemiluminescence (CL) detection. The CL signal produced by the emission of photons from luminol was directly proportional to the amount of analyte. The linear range was 0.45-7.5 ng dL(-1 )and the detection limit was 0.09 ng dL(-1). Experimental conditions, such as temperature, pH, incubation time, titration level and other relevant variables upon the CL signal have been examined and optimized. A coefficient of variance of less than 16% was obtained for intra- and inter-assay precision. The present method has been successfully applied to the analysis of FT4 in human serum. The positive and negative coincidence ratios are satisfactory. Good correlations were obtained between the results by the proposed method and radioimmunoassay (RIA), as well as a Bayer ACS-180SE detection system.

Effect of corticosteroid on salicylate-induced morphological changes of isolated cochlear outer hair cells.

Our previous studies showed that pretreatment with corticosteroids, which inhibits release of arachidonic acid (precursor of prostaglandins and leukotrienes), partially prevented salicylate-induced hearing loss in vivo. The purpose of this study was to determine the effect of pretreatment with corticosteroid (dexamethasone sodium phosphate) on isolated cochlear outer hair cells (OHCs) exposed to salicylate in vitro. Isolated OHCs from the chinchilla cochlea were exposed to salicylate with or without pretreatment with dexamethasone. Images were stored and analyzed on the Image program. The OHCs exposed to salicylate demonstrated a significant shortening in cell length. The OHCs exposed to salicylate after pretreatment with dexamethasone exhibited no significant change in cell length. We conclude that corticosteroid treatment of isolated OHCs is effective in blocking the morphological changes induced by salicylate. This study gives additional evidence that salicylate ototoxicity is mediated by alteration in the levels of arachidonic acid metabolites.

Effects of Ginkgo biloba extract (EGb 761) on cochlear vasculature in the guinea pig: morphometric measurements and laser Doppler flowmetry.

Ginkgo biloba extract (EGb 761) was administered orally for 4 or 6 weeks to healthy adult guinea pigs. Animals were then decapitated under deep ketamine anesthesia. Post-mortem morphometric measurements of cochlear vessels in the spiral lamina revealed a vasodilating effect of the extract in four of ten animals following 6 weeks of treatment. In vivo testing of the effect of 4 or 6 weeks of treatment with EGb 761 was monitored with laser Doppler flowmetry of the cochlear blood flow under pathological conditions. Results demonstrated that EGb 761 partly counteracted sodium salicylate-induced decreases in cochlear blood flow (CBF) and enhanced CBF increases induced by hypoxia. These findings indicate that EGb 761 may help to improve oxygenation in cochleas with compromised blood flow.

Effects of dietary sodium selenite supplementation on salicylate-induced embryo- and fetotoxicity in the rat.

The effects of dietary supplementation with sodium selenite (3.0 or 4.5 ppm Se) for 8 weeks prior to and throughout gestation on sodium salicylate induced embryo- and fetotoxicity (resorptions, fetal deaths, malformations, fetal weight reduction) have been studied in the rat. Salicylate was administered either as daily intragastric bolus doses of 250 mg/kg on gestation days 6-13 (maternal peak and trough salicylate levels of 222-120 micrograms/ml whole-blood) or via constant rate intravenous infusion of 150 mg/kg/day on the same gestation days via implanted osmotic minipumps (stable average maternal blood salicylate level of 120 micrograms/ml = human antirheumatic concentration). Both gavage and infusion of salicylate resulted in an increase of resorptions and fetal deaths as well as a decrease of fetal body weights. Gavage with salicylate also produced about 50% malformed fetuses. Selenite did not protect against the embryotoxic effects of salicylate administered as intragastric bolus doses. However, selenite was found to significantly increase fetal survival rate in the infusion experiment, although it did not counteract the decrease of fetal body weight. In animals fed selenite only, no negative effects on fetal body development were noted. The protective effect of selenite against salicylate induced embryotoxicity is difficult to explain, since very little is known about the mechanisms of salicylate embryotoxicity and the biological effects of selenium. However, an interaction between selenium, via glutathione peroxidase, and salicylate at the level of prostaglandin synthesis could be possible.

Protection against salicylate ototoxicity by zinc.

One day after oral application of 700 mg (5.5 mmol)/kg salicylic acid given as Na salicylate, hearing thresholds in rats, measured by acoustically evoked responses at 10 and 20 kHz, were increased. Salicylate-induced hearing loss was completely prevented by simultaneous s.c. injection of 6 mg (92 mumol)/kg Zn, whereas simultaneous s.c. injection of 1.5 mmol/kg MgCl2 had no effect. Simultaneous s.c. injection of 100 mg (152 mumol)/kg desferrioxamine had only a minor beneficial effect indicating that salicylate-induced Fe accumulation plays no significant role in salicylate ototoxicity.

[Mechanism of the species characteristics of the sensitivity of monkeys and dogs to the emetic action of various pharmacological agents]. / K mekhanizmu vidovykh osobennostei chuvstvitel'nosti obez'ian i sobak k émeticheskomu deistviiu razlichnykh farmakologicheskikh sredstv.

Monkey and dog sensitivity to the emetics that stimulate catecholamino- and serotoninoreactive structures of the chemoreceptor trigger zone (CTZ) of the vomiting center has been studied. It has been found that the monkeys are sensitive to the vomiting effect of serotonin agonists, while the dogs to the stimulants of the dopamino- and adrenoreceptors of the CTZ. At the same time both the monkeys and dogs are equally sensitive to the emetic action of sodium salicylate. The latter's effect has been shown to be realized via the serotoninergic structures of the CTZ in the monkeys, and via the adrenergic structures in the dogs. It is suggested that specific features of the monkey and dog responses to administration of central emetics are determined by the differences in the neurochemical structure of the CTZ, particularly by the prevalence of the serotonin- or catecholamine-containing neurons.

Effects of intracerebral micro-injection of sodium salicylate on temperature regulation in the rabbit.

1. Symmetrical, bilateral micro-injections (10 mul.) of 6-30 mug sodium salicylate have been made into various parts of the brains of febrile and afebrile rabbits.2. In rabbits with fever induced by an intravenous infusion of endogenous pyrogen, micro-injections of sodium salicylate produced antipyresis when given into the preoptic hypothalamus and the mid-brain.3. In afebrile rabbits, micro-injections of sodium salicylate into these areas were without effect on temperature.4. The results suggest that at least part of the antipyretic effect of salicylates may be mediated by antagonizing the effects of endogenous pyrogen within these areas of the brain.