The ovary of Penaeus japonicus Bate, 1888 (Custacea decapoda) is neither a target nor a source of progesterone.

The reproductive endocrinology of the kuruma shrimp, Penaeus japonicus, was investigated to establish whether progesterone exert a vitellogenesis-stimulating action and the ovary is an autonomous source of progesterone. Progesterone injected into adult, immature females (stages 1 and 2; 1 µg/g BW) failed to accelerate vitellogenesis and to promote ovarian growth with respect to controls during a 41-day observation period. Ovarian tissue (1 g) at stage 4 perifused with a medium devoid of steroid precursors did not release any significant amount of progesterone measurable by radioimmunoassay (<100 pg/g/h). When ovarian tissue (1 g) at stage 4 was incubated with 18.5 kBq of [4-14C]pregnenolone (0.9 µM) for 6 h, it produced progesterone (0.3% yield), 20-dihydropregnenolone (13.3%) and few other unidentified metabolites. Under the same conditions, [4-14C]dehydroepiandrosterone (1 µM) was converted to androstenedione (0.1%), testosterone (0.2%) and 5-androstene-3ß,17ß-diol (72%). Activity of key steroidogenic enzymes, such as cytochromes P450c17 and P450c21, was not detected. These data indicate that the mature ovary of P. japonicus is not an autonomous source of progesterone and possesses rather limited steroid-transforming capabilities. However, its extremely high level of 17-ketosteroid reductase activity, an enzyme crucial for testosterone biosynthesis in the mammalian testis, suggests that the shrimp ovary might be able to process and presumably activate prohormonal steroids of extraovarian origin.