ABSTRACT
Asterias rubens is able to synthesize steroids from cholesterol, progesterone and androstenedione as precursors. During the annual reproductive cycle the steroid synthesizing capacities of ovaries and pyloric caeca, taking the activity of 3β-HSD as a parameter, show a pronounced pattern of variation. The greater activity in the ovaries coincides with the presence of steroid synthesizing cells.
Progesterone, oestradiol-173 and oestrone are endogenous steroids. Variations in the levels of progesterone and oestrone related to the actual stage of the annual reproductive cycle, to the presence of steroid synthesizing cells, and to biochemical data, suggest that these steroids may have a physiological function.
It seems that oestradiol-17β, possibly after being converted into oestrone, affects the incorporation into oocytes of proteins or other substances originating from the pyloric caeca, and thus stimulates the vitellogenesis resulting in growth of oocytes of the starfish.
