ABSTRACT
Besides the general function in membranes, sterols have a special function as precursors for steroid hormones in vertebrates. Saponins of asteroids are structurally related to sterol sulphates, which are present in rather high concentrations. The holothuroids and asteroids are unique within the echinoderms in that they contain saponins called holothurins and asterosaponins, respectively. The asterosaponins of asteroids have many properties in common with the holothurins. Asterosaponins are generally considered to be offensive or defensive weapons and there is some evidence that saponins may be released more or less continuously from the tube-feet, with the result that the presence or approach of an asteroid is noticed at some distance by several marine animals. The sterol pattern of an animal is the result of an equilibrium between the processes which provide sterols, viz. de novo synthesis and absorption of dietary sterols, and the processes which eliminate sterols. The sterol pattern is a dynamic state influenced by several factors.
