17β-Hydroxysteroid Dehydrogenase Activity of Ovary and Hepatopancreas of Freshwater Prawn, Macrobrachium rosenbergii: Relation to Ovarian Condition and Estrogen Treatment

Abstract

The activity of 17β-hydroxysteroid dehydrogenase (17β-HSD) was determined in the hepatopancreas anti the ovary of freshwater prawn Macrobrachium rosenbergii , at different stages of life. A uniform level of 17β-HSD activity was observed in the hepatopancreas of immature, maturing, matured, and gravid prawns, whereas the activity of this enzyme was found to be higher in the ovary of the maturing prawn only. Gradual increases in the GSI values and ovarian protein content at the different stages of maturity were observed in this animal. Between the two organs, higher activity of 17β-HSD was observed in the hepatopancreas of the prawn in the maturing stage. The estradiol-17β (E2) level measured by radioimmunoassay showed its peak in both the hemolymph 126.0 ± 7.0 pg/ml) and the ovary (300.00 ± 9.0 pg/mg protein) in the maturing prawn only compared to that in immature, matured, and gravid prawns. The hormone level became undetectable in the hemolymph and remained about 10-fold less (30.6 ± 5.0 pg/mg protein) in the ovary of the gravid prawn in comparison to the prawns in the maturing stage. A parallelism between the nature of 17β-HSD activity and the hormone level was observed in the ovary at different stages of life. A dose-dependent stimulation of 17β-HSD activity was observed in the hepatopancreas of the maturing prawn after three consecutive injections of 0.25. 0.5, 1.0, and 2.0 μg/g of estradiol-17β (E2) on the 4th day of treatment compared to the control values. E2 at a higher dose (4.0 μg/g) caused only a little stimulation of 17β-HSD activity in this organ. The ovary of the maturing prawn showed a higher degree of responsiveness to E2 by increasing the activity of 17β-HSD in a dose-dependent manner, in the range of 0.05, 0.1, and 0.25 μg/g doses. A graded inhibition of the enzyme activity was observed in the ovary with higher doses of E2 (0.5, 1.0, and 2.0 μg/g). The E2-induced increase of 17β-HSD activity was neutralized by concurrent use of tamoxifen and cycloheximide. The present study suggests that the endogenous and E2-inducible nature of steroid metabolism probably through increased biosynthesis of 17β-HSD in the hepatopancreas and the ovary of the maturing freshwater prawn has a reproductive role.