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

Abstract

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, 20beta, 21-trihydroxy-4-pregnen-3-one (20beta-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 microg x 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 20beta-S and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) were purified. In other Teleost fish these steroids are biologically active as MIS. The 17,20beta-P was clearly detected in Mtg and M stages and confirmed by enzymatic oxidation with enzyme 20beta-HSD. The 20beta-S was strongly detected in all Mtg oocytes. The results do not corroborate 20beta-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 20beta-S is acting as a MIS in M. furnieri.

Determination of hormones inducing oocyte maturation in Chalcalburnus tarichi (Pallas, 1811)

“…Certain progestagens in fish are described as MISs due to the fact that they induce final oocyte maturation (FOM). Of these, 17,20b-P and/or 20b-S are known as steroids that induce oocyte maturation in most fish Garcia-Alonso et al 2004;Matsuyama et al 1998;Modesta and Canario 2002;Ohta and Matsuyama 2002;Yueh and Chang 2002;Webb et al 2002). However, in other fish species, different steroids may be effective in inducing oocyte maturation and ovulation.…”