Enzyme immunoassay for testosterone and androstenedione in culture medium from rabbit oocytes matured in vitro

Changes in circulating concentrations of testosterone and estrone sulfate after human chorionic gonadotropin administration and subsequent to castration of 2-year-old stallions

Reproductive steroids testosterone (T) and estrone sulfate (E1S) are used as diagnostic markers for cryptorchidism in horses. The human chorionic gonadotropin (hCG) stimulation test is used as a diagnostic aid because administration of this hormone results in greater incremental differences in circulating steroid concentrations. Thoughts regarding optimal sampling times following hCG administration, however, are inconsistent. Additionally, determination of half-life of these steroids is important in postsurgical samples to confirm complete removal of testicular tissue. Objectives of this study, therefore, were to determine optimal sampling periods for peak T and E1S after hCG administration and half-life of these steroids after castration. Eight pony stallions were randomly assigned to control or treatment groups (5000 IU hCG). Blood samples were collected following hCG administration. Subsequently, stallions were castrated and blood samples were collected post-castration. The T concentrations were greatest at 72 h after hCG and were greater (P < 0.02) in samples from hCG-treated than control animals: 9,903.4 ± 384 and 784.0 ± 192 pg/mL, respectively (Mean ± SEM). The T concentrations were also greater at 1, 12, 24, 48 and 96 h. The E1S concentrations did not change after administration of hCG. The T response to hCG administration was biphasic with a maximal response between 48-96 h after administration. Half-lives of T and E1S were 1.1 and 0.7 h, respectively, and concentration of T and E1S was similar to that of geldings at 24 h post-castration, which, therefore, should be considered an optimal time to ensure complete castration has occurred.

The distorting effect of varying diets on fecal glucocorticoid measurements as indicators of stress: a cautionary demonstration using laboratory mice

The physiological stress response is frequently gauged in animals, non-invasively, through measuring glucocorticoids in excreta. A concern with this method is, however, the unknown effect of variations in diets on the measurements. With an energy dense diet, leading to reduced defecation, will low concentrations of glucocorticoids be artificially inflated? Can this effect be overcome by measuring the total output of glucocorticoids in excreta? In a controlled laboratory setting we explored the effect in mice. When standard mouse chow - high in dietary fiber - was replaced with a 17% more energy-dense diet, fecal mass was significantly reduced. As circulating levels of corticosterone and the total output of corticosterone metabolites over time remained unaffected, the result was an overestimation - more than a doubling - of the corticosterone metabolite excretion if expressed as concentrations. Similar results were obtained for testosterone metabolites. Although measuring the total output is not feasible in, for example, wildlife studies, the present findings highlight the perilousness of relying on concentrations of hormones in excreta with no associated information of the dietary intake as even moderate changes can exert a great influence.

Development of an immunosensor for the detection of testosterone in bovine urine

In the presented work, a disposable immunosensor for the detection of testosterone, an endogenous steroid hormone, in bovine urine has been developed using screen-printed electrodes (SPEs). Due to concerns over the use of steroid hormones as growth promoters, the EU prohibits their use in food producing animals. Consequently, rigorous screening procedures have been implemented in all member states to detect the illegal administration of such compounds. Competitive immunoassays were developed, initially by enzyme linked immunosorbent assay (ELISA), and subsequently transferred to an electrochemical immunosensor format using disposable screen-printed carbon electrodes. Horseradish peroxidase (HRP) was the enzyme label of choice and chronoamperometric detection was carried out using a tetramethylbenzidine/hydrogen peroxide (TMB/H2O2) substrate system, at +100 mV. The EC50 values obtained for the assay in buffer and urine gave relatively comparable results, 710 pg mL(-1) and 960 pg mL(-1), respectively. The linear range obtained for the assay in buffer extended from 0.03 ng mL(-1) to 40 ng mL(-1); while that in urine ranged from 0.03 ng mL(-1) to 1.6 ng mL(-1). The corresponding limits of detection (LOD) in buffer and urine were 26 pg mL(-1) and 1.8 pg mL(-1). Cross reactivity profiles of the antibody have been examined, with notable cross reactivities with 19-nortestosterone (11.6%) and boldenone (9.86%). Precision studies for the sensor demonstrated adequate reproducibility (CV<13%, n=3) and repeatability (CV<9%, n=3). Recovery data obtained showed good agreement between spiking studies and known concentrations of analyte. Sensors showed stability for 4 days at +4 degrees C. A sensitive, highly specific, inexpensive, disposable immunosensor, showing excellent overall performance for the detection of testosterone in bovine urine, has been developed.

Amplified androstenedione enzymeimmunoassay for the diagnosis of cryptorchidism in the male horse: comparison with testosterone and estrone sulphate methods

An amplified enzymeimmunoassay (EIA) was validated for androstenedione in the serum of male horses. We will use the assay as a tool for the diagnosis of equine cryptorchidism. We will compare androstenedione EIA to the currently used methods (testosterone and estrone sulphate determinations). The study was conducted on 115 horses of pure Spanish and Arabian breeds, that included 30 geldings, 60 bilateral cryptorchids and 25 stallions. Androstenedione standard curve covered a range between 0 and 1 ng per well. Low detection limit was 1.54 pg/ml. Intra- and inter-assay coefficients of variation (CV%) were <8.2 and <9.3, respectively (n=10). Recovery rate of known androstenedione concentrations averaged from 96.62+/-2.69 to 97.63+/-1.87%. Androstenedione mean+/-S.E. serum concentrations were 10.52+/-1.36 ng/ml in stallions (n=25), 0.51+/-0.04 ng/ml in cryptorchids (n=60), and 0.03+/-0.01 ng/ml in geldings (n=30). Diagnostic validation parameters in basal samples showed for estrone sulphate the lower positive predictive value (0.85) with the higher number of false positives, and lower specificity (0.84). Testosterone showed the higher number of false negatives with a negative predictive value of 0.85, and lower sensitivity (0.85). Among the three hormones evaluated, androstenedione presented the best results with the smaller number of horses diagnosed as false positives (0.93) or negatives (0.91). This technique also resulted in higher sensitivity, specificity and efficiency over the other two methods assayed. We concluded that our amplified EIA is a highly sensitive and specific assay that provides a rapid, simple, and inexpensive alternative to other methods.