Equine 5α-reductase activity and expression in epididymis

Area of Science:

• Reproductive biology and endocrinology
• Steroid metabolism and enzyme activity
• Equine reproductive physiology

Background:

• 5α-reductase enzymes are vital for male sexual differentiation and, in equine pregnancies, for progesterone metabolism to 5α-dihydroprogesterone (DHP).
• The equine epididymis expresses 5α-reductases, but their specific roles and characteristics in horses remain underexplored.
• Understanding epididymal 5α-reductase activity is important for equine reproductive health and steroidogenesis.

Purpose of the Study:

• To investigate the activity and expression of 5α-reductase type 1 and type 2 isoforms in the equine epididymis.
• To determine the metabolic capacity of the equine epididymis for converting progesterone and testosterone.
• To evaluate the inhibitory effects of finasteride and dutasteride on equine epididymal 5α-reductase and examine pregnenolone as a potential substrate.

Main Methods:

• Quantitative real-time polymerase chain reaction (qPCR) was used to analyze 5α-reductase isoform expression in caput, corpus, and cauda epididymis from stallions.
• Enzyme activity was assessed by measuring the conversion of progesterone to DHP and testosterone to dihydrotestosterone (DHT) using thin-layer chromatography and LC-MS/MS.
• In vitro assays were performed to test the inhibitory potencies of finasteride and dutasteride and to investigate pregnenolone metabolism.

Main Results:

• No significant regional differences in 5α-reductase activity or transcript levels were found across the equine epididymis.
• Quantitative PCR indicated that the type 1 isoform of 5α-reductase predominates in the equine epididymis, with no detectable expression of the type 2 isoform.
• Equine epididymal microsomes efficiently converted progesterone to DHP and testosterone to DHT, with activity significantly inhibited by both finasteride and dutasteride. Pregnenolone was not found to be a direct substrate.

Conclusions:

• The equine epididymis primarily expresses 5α-reductase type 1, which is responsible for the metabolism of progesterone and testosterone to DHP and DHT, respectively.
• The study provides no evidence that pregnenolone is directly metabolized by equine epididymal 5α-reductases, challenging previous hypotheses regarding DHP synthesis pathways.
• These findings enhance our understanding of steroid metabolism in the equine epididymis and its implications for reproductive physiology.