SEX STEROIDS IN TAPES PHILIPPINARUM (ADAMS AND REEVE, 1850) DURING THE GAMETOGENIC CYCLE : PRELIMINARY RESULTS.

It is well known that a wide variety of endocrine disruptor chemicals (EDCs) (e.g., organotin compounds, heavy metals, herbicides, and xenoestrogenic compounds) can induce endocrine abnormalities in marine invertebrates often causing reproductive disorders. Despite these phenomena are of great concern mostly in coastal and estuarine environments, only few data are available about the mechanism of action of EDCs, mainly due to a lack of knowledge on the invertebrate endocrine system. In particular, in the clam Tapes philippinarum estrogenic effects of nonylphenol (NP) were recently demonstrated, they resulting in vitellogenin-like protein induction, mostly in male clams (Matozzo and Marin, 2005), as NP probably mimics endogenous estrogens. To better understand the possible mechanism of action of NP, as well as of other EDCs, the presence and patterns of variation of sexual steroids were evaluated during the various phases of the gametogenic cycle of T. philippinarum. Adult clams were collected from two licensed areas located in the Lagoon of Venice (Italy) from July 2005 to May 2006, corresponding to following stages: spawning (July), post-spawning (October), spent (January) and gametogenesis (May). The clams were sexed by microscopic observation (400×) of a smear of gonadal tissue with the exception of the spent stage in which no gametes were detectable. Progesterone, testosterone and estradiol-17b were measured in the whole-body clam homogenate using specific and opportunely validated microtitre RIAs. Differences in hormone concentrations during annual cycle were assessed by analysis of variance (ANOVA) followed by a Tukey’s Post hoc test (P<0.05). In females, all the hormones showed the same profile, with higher concentrations during the spawning period and lower during post-spawning and gametogenesis. In males, progesterone and estradiol-17b never differed among stages and the values were very similar to those of females in non spawning periods. Conversely, testosterone statistically decreased during gametogenesis. All the hormones were unexpectedly high in the spent stage in which no gonadal tissue was observable and females and males were thus jointly processed. Progesterone was the most representative sexual steroid showing levels (about 1 ng/g) six to seven times higher than those of estradiol-17b and testosterone. Although the results obtained are preliminary and need further validation, the protocols set up to evaluate sexual steroids in T. philippinarum represent the first step for future research aimed at understanding the physiological role of these hormones and their potential interaction with EDCs. Matozzo V., Marin M.G., 2005. Can 4-nonylphenol induce vitellogenin-like proteins in the clam Tapes philippinarum? Environ. Res., 91: 179-185.