Equine 5α-reductase activity and expression in epididymis.

This research explores the functioning and expression of the 5α-reductase enzymes in the epididymis of male horses, focusing specifically on the metabolism of progesterone and testosterone to 5α-dihydroprogesterone (DHP) and dihydrotestosterone (DHT) respectively, and the inhibitory effects of certain substances.

Background and Purpose of the Study

• The 5α-reductase enzymes are crucial in male sexual differentiation and in pregnancy, particularly in horses where the maintenance of pregnancy depends largely on 5α-reduced progesterone, known as DHP.
• The epididymis, a part of the male reproductive system, is known to express 5α-reductases but this has not previously been studied in depth in horses.
• The aim of the study was to explore 5α-reductase activity and the expression of type 1 and 2 isoforms in the epididymis of both younger and older post-pubertal stallions.

Methodology

• The epididymis from the stallions was divided into three parts (caput, corpus and cauda) and examined for 5α-reductase activity.
• Expression of type 1 and 2 isoforms was investigated by quantitative real-time polymerase chain reaction (qPCR).
• The metabolism of progesterone and testosterone to DHP and DHT, respectively, was examined via thin-layer chromatography and confirmed through liquid chromatography tandem mass spectrometry (LC-MS/MS).
• The research also looked at the inhibitory impacts of two substances, finasteride and dutasteride, on equine 5α-reductase activity.
• Pregnenolone was also considered as another potential substrate for 5α-reductase, as previous in vivo studies in mares suggested but did not directly examine.

Findings

• There was no observed regional gradient of 5α-reductase expression, either by enzyme activity or transcript analysis.
• Results from the PCR experiments indicated that the type 1 isoform is more dominant in the equine epididymis.
• The primers for the type 2 isoform were unable to generate products from any samples examined, suggesting its non-existence or very low levels.
• Both progesterone and testosterone were efficiently reduced to DHP and DHT, illustrating the active role of the enzyme.
• Both finasteride and dutasteride effectively inhibited this enzyme activity.
• No experimental evidence was found to support the idea that pregnenolone could be directly metabolized by equine 5α-reductases, contradicting the suggestions of previous research.