Abstract
BackgroundDuring female reproductive cycles, a rapid fall in circulating progesterone (P4) levels is one of the earliest events that occur during induced luteolysis in mammals. In rodents, it is well recognized that during luteolysis, P4 is catabolized to its inactive metabolite, 20alpha-hydroxyprogesterone (20alpha-OHP) by the action of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) enzyme and involves transcription factor, Nur77. Studies have been carried out to examine expression of 20alpha-HSD and its activity in the corpus luteum (CL) of buffalo cow.MethodsThe expression of 20alpha-HSD across different bovine tissues along with CL was examined by qPCR analysis. Circulating P4 levels were monitored before and during PGF2alpha treatment. Expression of 20alpha-HSD and Nur77 mRNA was determined in CL at different time points post PGF2alpha treatment in buffalo cows. The chromatographic separation of P4 and its metabolite, 20alpha-OHP, in rat and buffalo cow serum samples were performed on reverse phase HPLC system. To further support the findings, 20alpha-HSD enzyme activity was quantitated in cytosolic fraction of CL of both rat and buffalo cow.ResultsCirculating P4 concentration declined rapidly in response to PGF2alpha treatment. HPLC analysis of serum samples did not reveal changes in circulating 20alpha-OHP levels in buffalo cows but serum from pseudo pregnant rats receiving PGF2alpha treatment showed an increased 20alpha-OHP level at 24 h post treatment with accompanying decrease in P4 concentration. qPCR expression of 20alpha-HSD in CL from control and PGF2alpha-treated buffalo cows showed higher expression at 3 and 18 h post treatment, but its specific activity was not altered at different time points post PGF2alpha treatment. The Nur77 expression increased several fold 3 h post PGF2alpha treatment similar to the increased expression observed in the PGF2alpha-treated pseudo pregnant rats which perhaps suggest initiation of activation of apoptotic pathways in response to PGF2alpha treatment.ConclusionsThe results taken together suggest that synthesis of P4 appears to be primarily affected by PGF2alpha treatment in buffalo cows in contrast to increased metabolism of P4 in rodents.
Highlights
During female reproductive cycles, a rapid fall in circulating progesterone (P4) levels is one of the earliest events that occur during induced luteolysis in mammals
The mRNA expression was high in the corpus luteum (CL) and the expression was detectable in spleen, brain and liver
It is well documented that the initial decrease in luteal function that occurs post PGF2α treatment is precipitated by an increase in P4 metabolism i.e. P4 gets converted to its inactive metabolite 20α-OHP rather than a decrease in its synthesis [9]
Summary
A rapid fall in circulating progesterone (P4) levels is one of the earliest events that occur during induced luteolysis in mammals. Catabolism of progesterone (P4) to its inactive metabolite, 4-Pregnen-20α-ol-3-one i.e. 20α-hydroxyprogesterone (20α-OHP) has been suggested to be one of the key mechanisms for regulation of circulating P4 concentration both in maternal and fetal compartments [1,2,3]. The activity of 20α-HSD in placenta was observed to be higher with a corresponding increase in the concentration of 20α-OHP in the fetal compartment during late pregnancy [3]. In many of these species, the observation of increased 20α-OHP levels in the placenta is suggestive of regulation of P4 concentration by the feto-placental unit and/or parturition process. Induction of 20α-HSD expression in the corpus luteum (CL) is one of the striking features of luteolysis that occurs immediately prior to parturition and lactogenesis in pregnant rats [6,7]
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