Steroid metabolism in vitro during final oocyte maturation in white croaker Micropogonias furnieri (Pisces: Sciaenidae)

JAVIER GARCÍA ALONSO; A NAPPA; GUSTAVO M SOMOZA; A REY; DENISE VIZZIANO,

BRAZILIAN JOURNAL OF BIOLOGY

INTERNATIONAL INSTITUTE OF ECOLOGY

Año: 2004 vol. 64 p. 211 - 220

1519-6984

Final oocyte maturation (FOM) is a process involving a complex set of genetical, biochemical, and morphological mechanisms. FOM involves the shift of a post-vitellogenic follicle to a pre-ovulated oocyte, which is necessary for fertilization by spermatozoan to occur. This process is regulated by a maturation-inducing steroid (MIS) at the follicular level. In other species of scienids fish the MIS, a hydroxilated derivatives of progestagen 17, 20b, 21-trihydroxy-4-pregnen-3-one (20b-S), was identified. Although Micropogonias furnieri is the second fishery resource of Uruguay, basic knowledge about its endocrine process is very scarce. The aim of this work was to investigate what steroids are synthesized in vitro by the oocyte follicle of M. furnieri during the maturation process. Fragments of ovary (1 g) in three stages: post-vitellogenic (PV), maturing (Mtg), and mature (M) were incubated with 1 mg.g-1 of tritiated progesterone (P) at 30, 60, and 180 min. After extraction with ethanol and dichloromethane, steroid metabolites were purified by TLC and rpHPLC. Two progesterone derivatives with identical chromatographic properties of 20b-S and 17,20b-dihydroxy-4-pregnen-3-one (17,20b-P) were purified. In other Teleost fish these steroids are biologically activ as MIS. The 17,20b-P was clearly detected in Mtg and M stages and confirmed by enzymatic oxidation with enzyme 20b-HSD. The 20b-S was strongly detected in all Mtg oocytes. The results do not corroborate 20b-S as a major hormone synthesized in the ovary in FOM as occurs in other scienid fish. A differential steroid synthesis in the advanced oocyte stages suggests that the 20b-S is acting as a MIS in M. furnieri.