In vitro and in vivo studies of androst-4-ene-3,6,17-trione in horses by gas chromatography-mass spectrometry.

The article discusses the use of Gas Chromatography-Mass Spectrometry (GC-MS) for studying the metabolism of 6-OXO in horses, in order to find the best detection method for its regulation in racehorses.

Research Methodology

• The study was conducted both in vitro (in a controlled laboratory environment) and in vivo (within living organisms). The in vitro study was done using horse liver microsomes to simulate the metabolism process.
• For the in vivo study, two thoroughbred geldings (castrated male horses) were orally administered with 500 mg of 6-OXO (androst-4-ene-3,6,17-trione). The administration was done by stomach tubing, a method used often for horses.

In Vitro Findings

• The primary biotransformation observed was the reduction of a keto group at the C3 or C6 positions.
• Three in vitro metabolites were identified, named M1, M2a, and M2b, revealing the biotransformation process of 6-OXO in a controlled environment.

In Vivo Findings

• The results of the in vivo study showed that 6-OXO was extensively metabolized within the horses. The three metabolites identified in the in vitro study were all found in urine samples taken after administration of 6-OXO.
• Additionally, seven other urinary metabolites were detected, which were a result of further reduction of the remaining keto group or a reaction with the olefin group. These were named M3a, M3b, M3c, M4a, M4b, M5, and M6.
• For the detection of the metabolite in the horses’ system, M6 had the longest detection time in urine, up to 46 hours.

Plasma Concentration Findings

• During the study, the peak 6-OXO plasma concentration was noted 1 hour post administration.
• The plasma concentration of 6-OXO decreased rapidly and was undetectable 12 hours after administration. This indicates the speed and efficiency at which horses metabolize the substance.

In summary, the researchers have identified the key metabolites to track for monitoring the administration of 6-OXO in horses, which is crucial for doping controls in horse racing. The findings indicate that monitoring urinary metabolites (particularly M6) is a reliable method, considering their longer detection window.