Atrial natriuretic peptides are a family of peptides which throughout the animal kingdom are synthesized mainly in the atria of the heart and have sodium excreting (natriuretic) properties. Within invertebrates these peptides` molecular species is very similar to that found within vertebrates. The gene producing these peptides has been isolated within invertebrates as well as vertebrates indicating that the atrial natriuretic peptides are synthesized within invertebrates as well. Increase in the salinity of the environment of marine invertebrates increases the concentration of atrial natriuretic peptides within the heart, gills, and hemolymph of these invertebrates while decreasing the external salinity decreases the concentration of atrial peptides in the heart, gills and hemolymph of oysters and crabs. Atrial natriuretic peptides are also present throughout the plant kingdom within leaves, flowers, stems and roots of plants. The molecular forms of atrial natriuretic peptides within the plant kingdom are very similar to those found in the animal kingdom. Within plants, atrial natriuretic peptides enhance the flow of water and solute upward via increasing transpiration. They also increase the absorption of water. With even single cell plants (i.e., Euglena) and single cell organisms in the animal kingdom (i.e., Paramecium) containing these peptides suggests that atrial natriuretic peptides evolved very early in evolution.
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