Seasonal dynamics,kinetics,and effects of 2-hydroxyestradiol-17βon some steroidogenic enzymes in the ovary of the catfish Heteropneustes fossilis

The synthesis of bioactive steroids is catalyzed by an array of enzymes of diverse properties and actions.In the present study,seasonal dynamics and kinetics of key steroidogenic enzymes,17α-hydroxylase(Cyp17a),3β-hydroxysteroid dehydrogenase(Hsd3b),20α-hydroxysteroid dehydrogenase(Hsd20a)and 20β-hydroxysteroid dehydrogenase(Hsd20b)were investigated in the female catfish Heteropneustes fossilis.Further,the effects of the estrogen metabolite 2-hydroxyestradiol-17β(2-OHE2)and human chorionic gonadotropin(hCG)on activities of the above enzymes,cytochrome P450 aromatase(Cyp19a1),and steroid products including testosterone and cortisol were determined.The enzymes under investigation showed significant seasonal variations across the annual ovarian cycle with low activity in the gonad resting phase.The enzymes Hsd3b and Cyp17a showed high activity during early oogenesis but the activities of Hsd20a and Hsd20b were higher towards late oogenesis in the spawning phase.Hsd3b and Cyp17a elicited high apparent Km values(low substrate affinity)and high apparent Vmax in the vitellogenic phase compared to the postvitellogenic phase.Hsd20a did not elicit any significant differences in the kinetic parameters between the two phases.Hsd20b showed high apparent Km values(low substrate affinity)and high Vmax in the postvitellogenic phase.The incubation of ovarian slices with 2-OHE2 for 24 h increased dose-dependently Hsd3b,Cyp17a,Hsd20a and Hsd20b activities,similar to hCG.The levels of the corresponding C21 steroid products,progesterone(P4),17α-hydroxyprogesterone(17-OHP4),17,20α-dihydroxy-4-pregnen-3-one(17,20α-DP)and 17,20β-dihydoxy-4-pregnen-3-one(17,20β-DP),and cortisol were elevated.However,2-OHE2 decreased significantly the C19 and C18 steroids,testosterone and E2 levels,and Cyp19a activity.The co-incubation with hCG and 2-OHE2 produced a synergistic effect on the enzyme activities except that of CYP19a.The co-incubation reversed the inhibitory effect of 2-OHE2.The data show that 2-OHE2 exerts a dual role on steroidogenesis,stimulating the C21 pathway and inhibiting the C19-C18 pathway,resulting in the steroidogenic shift.

Impact of ovariectomy and estradiol-17β(E_(2))replacement on the brain steroid levels of the Indian stinging catfish Heteropneustes fossilis

In the present study,effects of ovariectomy(Ovx)and estradiol-17β(E2)replacement on the brain steroid levels were investigated in the resting and prespawning phases of the female catfish Heteropneustes fossilis.The study showed that Ovx resulted in significant decreases in plasma levels of estradiol-17β(E2)and its precursors,and the effect varied with the reproductive stage and duration.Our study showed that E2 supplementation reversed the effect of Ovx in 3-week Ovx fish group,either restored or increased according to the dose.In contrast,E2 levels increased in the brain after Ovx in the resting stage and produced a biphasic effect of significant decreases on week 1 and 2,and significant increases on week 3,4 and 5 in the pre-spawning stage.The brain E2 levels significantly inhibited in E2 supplementation groups.The testosterone(T)levels showed biphasic effects,an initial decrease(up to 3 weeks Ovx)and an increase later(week 4,5)in the resting stage.In the pre-spawning stage,the T levels increased significantly after Ovx.The E2 supplementation significantly inhibited the T levels,more severely in the low dose group in the resting and pre-spawning stages.Brain 17-hydroxyprogesterone(17-OHP4)levels increased(week 1,2,3)but decreased on week 4 and 5 of Ovx in the resting stage and increased throughout Ovx in the pre-spawning stage except in the 5th week(though compared to other steroids,level was very low;almost negligible).The E2 replacement significantly decreased the steroid levels further down compared to the Ovx control group.Brain progesterone(P4)and pregnenolone(P5)levels decreased initially(week 1 and 2 Ovx)and recovered later.The E2 replacement significantly decreased P4 levels in the Ovx fish in the pre-spawning stage and in the lower dose group in the resting stage.The P5 levels remained inhibited after the E2 supplementation in the resting stage but unchanged or increased it in the pre-spawning stage.Brain cortisol(F)levels were inhibited initially(1 and 2 weeks and later increased after OVX in the resting stage.In the pre-spawning stage,the F levels increased in the week 1,2 and 3 of Ovx and decreased in the 4th and 5th weeks.The E2 supplementation inhibited the cortisol(F)levels in both phases.The results show that ovarian steroids influence neurosteroidogenesis in a reproductive stage-dependent manner.