Comparative Endocrinology of Steroid Hormones in Vertebrates

Abstract

Recent advances in biochemical techniques have resulted in considerable progress in the comparative qualitative analysis of non-mammalian vertebrate steroids. The literature surveyed herein suggests that a number of C21, C19, and C18 steroids occur throughout the subphylum. although there may be important qualitative differences even among closely related forms. The potential importance, from a phylogenetic or a physiological standpoint, of new steroids recently characterized in fishes cannot be evaluated at present. Three widely used techniques—tissue extraction or incubation without added precursors, tissue incubation with exogenous steroid substrates, and the histochemical visualisation of 3βhydroxysteroid dehydrogenases—are discussed, and their application to the study of steroidogenic tissues is illustrated. The adrenocortical homologue (interrenal), the ovary, and the testis appear to function as sources of steroid hormones in those vertebrates which have been examined. However, the existence of additional steroidogenic tissues, or of tissues which may modify the steroid composition of the body fluids in other ways, is also suggested.