Inhibition of 5α-reductase alters pregnane metabolism in the late pregnant mare

Abstract

In the latter half of gestation in the mare, progesterone concentrations decline to near undetectable levels while other 5α-reduced pregnanes are elevated. Of these, 5α-dihydroprogesterone and allopregnanolone have been reported to have important roles in either pregnancy maintenance or fetal quiescence. During this time, the placenta is necessary for pregnane metabolism, with the enzyme 5α-reductase being required for the conversion of progesterone to 5α-dihydroprogesterone. The objectives of this study were to assess the effects of a 5α-reductase inhibitor, dutasteride on pregnane metabolism (pregnenolone, progesterone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol and allopregnanolone), to determine circulating dutasteride concentrations and to assess effects of dutasteride treatment on gestational parameters. Pregnant mares ( = 5) received dutasteride (0.01 mg/kg/day, IM) and control mares ( = 4) received vehicle alone from 300 to 320 days of gestation or until parturition. Concentrations of dutasteride, pregnenolone, progesterone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol, and allopregnanolone were evaluated via liquid chromatography-tandem mass spectrometry. Samples were analyzed as both days post treatment and as days prepartum. No significant treatment effects were detected in pregnenolone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol or allopregnanolone for either analysis; however, progesterone concentrations were increased ( < 0.05) sixfold in dutasteride-treated mares compared to control mares. Dutasteride concentrations increased in the treated mares, with a significant correlation ( < 0.05) between dutasteride concentrations and pregnenolone or progesterone concentrations. Gestational length and neonatal outcomes were not significantly altered in dutasteride-treated mares. Although 5α-reduced metabolites were unchanged, these data suggest an accumulation of precursor progesterone with inhibition of 5α-reductase, indicating the ability of dutasteride to alter progesterone metabolism.

Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares

“…Early studies identified 5a-reduced androstanediols in urine from pregnant mares [62] and B-ring unsaturated androgens [63,64] that to our knowledge have never been quantified in equine blood for instance. Considering the levels of expression and activity of 3bHSD and 5a-reductase in the equine placenta and endometrium [28,37,65], it seems likely that 5a-reduced androgens are more likely candidates to be secreted in relatively high concentrations. Further investigation will be necessary to identify what (if any) sulphated androstanes are secreted during equine gestation, perhaps requiring gas chromatography mass spectrometry as a more powerful discovery tool [20,66].…”

Steroids in the establishment and maintenance of pregnancy and at parturition in the mare

“…Logically, the apparent loss of 5α-reductase activity in the placenta at foaling would be expected to decrease metabolism of progesterone overall. Indeed, inhibition of 5α-reductase activity in the late pregnant mare is associated with an increase in maternal and foetal progesterone concentrations (Wynn et al 2018a). Yet, at term, progesterone reappears in maternal blood (Fig.…”

Saliva and plasma steroidome in mare during reproductive stages: A GC-MS/MS study

“…pregnant mare (Wynn et al, 2018a) and in foals (Müller et al, 2019). However, our study is the first to perform a complete analysis of PROG metabolites in equine saliva and plasma.…”

“…For example, progesterone (PROG) and 17b-estradiol (17b-E2) measurements in plasma of cyclic mares by enzyme immunoassay and radioimmunoassay, respectively, showed that concentrations of PROG begin to increase the day of ovulation, reach maximal concentrations at 6 to 8 days post-ovulation and decrease until day 14 post-ovulation whereas concentrations of 17b-E2 reach a peak 2 days before ovulation and then decrease (Ginther et al, 2005;Aurich, 2011). Gas chromatography coupled to mass spectrometry (GC-MS), liquid chromatography coupled to mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS/ MS) analysis have been developed to measure some pregnanes (C21-steroids), androstanes (C19-steroids) and estranes (C18steroids) in serum of male and female uncharacterized horses (Genangeli et al, 2017;Dufour et al, 2021) and in plasma throughout equine gestation (Scholtz et al, 2014;Legacki et al, 2016;Wynn et al, 2018a;Ledeck et al, 2022). Analysis in pregnant mares showed that plasmatic PROG concentrations were high during the first 12 weeks of pregnancy and declined progressively until undetectable levels by day 200.…”