The endocrinology of invertebrates

Neuroendocrine controls exist already in lower invertebrates, and during evolution, endocrine glands have appeared in molluscs, although endocrine cells may have appeared earlier. The present review discusses at first the different strategies used in the past and nowadays to isolate hormones and to analyze their functions. Both peptidic and lipidic hormones have been found in invertebrates, just as in vertebrates. Some of these hormones are specific of invertebrates, whereas other ones may be very close to their vertebrate counterparts. However, hormonal functions are less conserved than structures, a fact that is also apparent within vertebrate hormones, depending on which tissues possess receptors and are therefore their targets. Some examples of hormone families (peptides, steroids, terpenes) are described. Xenobiotics disturb normal cell functions, and they may accordingly alter endocrine systems, either at the endocrine cells or at the target cell levels. This will be illustrated by a few characteristic examples. However, the rather fragmentary knowledge of invertebrate (except insect) endocrinology prevents in many cases an adequate understanding of the mechanisms involved in xenobiotic toxicity.