mone vasotocin is also present in all of these groups. In the Amphibia corticosterone and aldosterone clearly playa role in regulating the conservation and accumulation of sodium. Vasotocin facilitates rehydration and the preservation of body
water, especially in terrestrial species. The kidney of amphibians, like that of all
vertebrates, plays a central role in osmoregulation, but additional processes at extrarenal sites are also very important in this group. It is at such non-renal sites that
the peptide and steroid hormones have a particularly prominent action. The Amphibia probably best illustrate the oft-quoted dictum that it is not the hormones
that have evolved but the uses to which they have been put. These uses, when compared with the fishes, would appear to include actions at sites like the skin, urinary
bladder, and the renal tubular epithelium where they have the novel effect of facilitating water conservation. It seems likely that, in addition, at least one new hormone, aldosterone, may have evolved; this is concerned with sodium conservation,
acting especially at extrarenal sites.
197
water, especially in terrestrial species. The kidney of amphibians, like that of all
vertebrates, plays a central role in osmoregulation, but additional processes at extrarenal sites are also very important in this group. It is at such non-renal sites that
the peptide and steroid hormones have a particularly prominent action. The Amphibia probably best illustrate the oft-quoted dictum that it is not the hormones
that have evolved but the uses to which they have been put. These uses, when compared with the fishes, would appear to include actions at sites like the skin, urinary
bladder, and the renal tubular epithelium where they have the novel effect of facilitating water conservation. It seems likely that, in addition, at least one new hormone, aldosterone, may have evolved; this is concerned with sodium conservation,
acting especially at extrarenal sites.
197