Use of enzyme-linked immunosorbent assay and radioimmunoassay to determine serum and urine dexamethasone concentrations in thoroughbreds after intravenous administration of the steroid.

The study outlined here develops a simplified and enhanced enzyme-linked immunosorbent assay (ELISA) for detecting dexamethasone in horse serum and urine. This has potential utility in the racing horse industry as it requires no specialized equipment or sample preparation.

Research Methods and Participants

• The researchers conducted this study using three thoroughbred mares from whom blood and urine samples were collected.
• A compound known as dexamethasone oxime was synthesized and then conjugated to various proteins – keyhole limpet hemocyanin, bovine serum albumin, and horseradish peroxidase.
• Several assay methods were then employed, including a one-step and a two-step double-antibody ELISA method, alongside a radioimmunoassay method.

Administration of Dexamethasone and Assay Testing

• The horses were intravenously administered with 5 mg of dexamethasone and the one-step ELISA was employed to carry out a test on the collected urine samples.

Results and Conclusions

• The ELISA was capable of detecting dexamethasone in concentrations ranging from 0.01 to 50 ng/ml, indicating a high level of sensitivity. The variations recorded within the assay and between different assays were 8.92% and 9.42%, respectively.
• Following the administration of the dexamethasone, peak serum dexamethasone concentrations of 20 to 35 ng/ml were observed just 15 minutes after and decreased to 1 ng/ml in 2.5 hours.
• In the urine samples, dexamethasone concentrations were measured in the range of 18 to 50 ng/ml 1 to 2 hours after dexamethasone administration and lowered to 1 ng/ml 10 hours post-administration.
• The sensitivity and simplicity of the newly developed ELISA method for detecting dexamethasone made it a comparable alternative to radioimmunoassay.
• Given the non-requirement of sophisticated equipment or sample preparation, the researchers concluded that this method can have practical applications in the racing horse industry where regular and convenient testing is a requisite.