Comparative Aspects of Estrogen Biosynthesis and Metabolism and the Endocrinological Consequences in Different Animal Species

Abstract

Steroidal estrogens have been isolated from marine and terrestrial animals representative for all major classes of vertebrates including fish, amphibians, reptiles, birds and mammals. In general, estrogens are responsible for most features characteristic of the female sex of a species, such as metabolic, behavioral and morphological changes during the steps of reproduction; they also support several events in the males. Other steroids are very common in all living organisms, with the exception of bacteria (Dorfman and Ungar 1965; Fieser and Fieser 1967). Although quite a number of functions of the various steroids was evolved, it is generally accepted, nowadays, that the endocrine functions of estrogens are a phenomenon of all vertebrates and, usually, estradiol-17 estradiol-17 β is the most potent endogenous substance. However, there are indications that estrogens are involved in the ovarian activities of non-vertebrate deuterostomic and even protostomic animals, but the function of estrogens in invertebrates is unclear. More recent literature considering these animals is very limited and, according to our knowledge, the presence of aromatase or the estradiol receptor is not yet documented for invertebrates. It is also generally accepted that, at least in plants, estrogens have no “estradiol-like” endocrine function during plant reproduction and the numerous phytoestrogens (Hesse et al. 1981) - which interact with mammalian estrogen receptors due to their structural similarities with estradiol - seem to have many other functions in the plant, such as protection against herbivory or oxygen stress similar to other phenols, condensed tannins or further secondary plant compounds (McArthur et al. 1993, Jung 1977, Feeny 1976