Biophysiology of natriuretic peptides in the evolutionary varieties of vertebrate osmoregulatory systems from shark rectal to mammalian salivary glands

Natriuretic peptides (NPs), guanylin, uroguanylin, heat-stable enterotoxin type a (STa), and the cystic fibrosis transmembrane conductance regulator (CFTR) are important regulators involving water and ionic balance in vertebrates. The present report points out the evolution of osmoregulatory systems and their effector organs, including the rectal glands of eels, frogs, and sharks; the salt glands of birds; and the salivary glands of mammals, including those of humans. Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and the activity of their respective receptors in the organs of vertebrates were reported as biological characteristics of heart hormone. This review focuses on Cl-/HCO3- exchange activity in the salivary gland ducts and ductal basal cells that express NPs and related regulators. This report describes published histochemical findings on protein and mRNA expression in ductal basal cells and the biological significances of those findings with regard to the mammalian salivary gland duct system and a number of growth factors synthesized in the granular convoluted tubules (GCT).