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Analysis of Epididymal Protein Synthesis and Secretion
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Equine 5α-reductase activity and expression in epididymis.

C J Corbin1, E L Legacki1, B A Ball2

  • 1Department of Population Health and ReproductionSchool of Veterinary Medicine, University of California, Davis, California, USA.

The Journal of Endocrinology
|July 29, 2016
PubMed
Summary

Equine epididymis contains 5α-reductase type 1, crucial for converting progesterone to 5α-dihydroprogesterone (DHP) and testosterone to dihydrotestosterone (DHT). This study confirms its role and explores potential substrates.

Keywords:
epididymisequinepregnancyprogesteronereductasesteroidogenesistestosterone

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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.