Sex steroids in tapes philippinarum (Adams and Reeve 1850) during the gametogenic cycle: preliminary results.

It is well known that a wide variety of endocrinedisrupting chemicals (EDCs) (e.g. organotin compounds, heavy metals, herbicides, xenoestrogen compounds) can induce endocrine alterations in aquatic invertebrates, often causing reproductive disorders. Although these phenomena are of great concern, mostly in coastal and estuarine environments, few data are available about the mechanism of action of EDCs, mainly due to lack of knowledge about the invertebrate endocrine system. To understand the possible mechanism of action of EDCs better, the presence and patterns of variation of sexual steroids, progesterone, testosterone and 17β-estradiol were measured in the whole body of the clam Tapes philippinarum by specific and opportunely validated microtitre radioimmunoassays (RIAs). Female steroid concentrations showed similar trends, with higher values during spawning and lower ones in post-spawning and gametogenesis periods. Conversely, in males, sexual steroids varied over the year: progesterone remained unchanged, with values similar to those of females in gametogenesis, whereas testosterone and 17β-estradiol showed a significant decrease during gametogenesis only. Seasonal variations in clam steroid levels may reflect their role in modulating reproduction. All hormones were unexpectedly high in the resting/ early developing stage, during which gonadal tissue is scarce, indicating that digestive gland may have a biosynthetic steroid capacity or accumulation. Although these results are preliminary, evaluation of sexual steroids in T. philippinarum during the gametogenic cycle represent the first step for future research aimed at understanding the physiological role of these hormones and their potential interaction with EDCs.