Studies related to the metabolism of anabolic steroids in the horse: the phase I and phase II biotransformation of 19-nortestosterone in the equine castrate.

This study is about understanding the biotransformation process of the anabolic steroid 19-nortestosterone in horses, highlighting the distinct pathways and products within the metabolism.

Introduction to the Study

• The research is based on examining the metabolism of 19-nor[4-14C]testosterone, an anabolic steroid, in horses. The investigation focuses primarily on the castrated equine, observing the process known as biotransformation, the chemical alteration of chemicals such as pharmaceuticals in the body.

Methodology

• The team employed a XAD-2 extraction method on 0-24 h urine samples for the evaluation. After extraction, the researchers managed to isolate glucuronic acid and sulphate conjugates, which are products of metabolism relating to the removal of drugs from the body, utilising Sephadex LH-20 column chromatography.
• Phase I metabolites (the first stage of drug metabolism, where enzymes chemically change or modify the drug) of 19-nortestosterone were then extracted and purified. Following this, gas-liquid chromatography (GLC) and mass spectrometry were utilised to precisely identify these metabolites.

Key Findings

• In the Phase I metabolism, the research found a distinct stereospecificity, a property of molecules having the same molecular formula but differ in the three-dimensional orientation of their atoms in space, in the A-ring reduction resulting in the formation of 5 alpha and 3 beta-isomers of estranediol.
• Epimerization at carbon-17 and hydroxylation at carbon-16 were also observed as major pathways in the metabolic process. Epimerization pertains to the conversion of one stereoisomer to another while hydroxylation is the chemical process that introduces a hydroxyl group (-OH) into an organic compound.
• In the Phase II metabolism, the research revealed that C-17 alpha steroid epimers were mainly conjugated with glucuronic acid, and C-17 beta epimers with sulphuric acid. Conjugation is the process where chemicals combine with another compound to facilitate their removal from the body.
• One anomaly in the study was an individual animal that exhibited variations in metabolism, showing a propensity towards the formation of polar metabolites, which is a product of metabolism that contrasts in polarity to their respective substrate.