ABSTRACT
The regulation of sodium balance results from a complex interplay between extrarenal and
intrarenal factors affecting either salt intake or sodium excretion. These mechanisms are
crucial to maintain body fluid homeostasis because the sodium ion is the main determinant
of extracellular fluid volume. Most of these extra-and intrarenal factors are under the
influence of endocrine, paracrine, and autocrine systems, which contribute to the regulation
of sodium balance either through their effects on blood pressure and renal perfusion or
because they exert direct effects on renal tubular transport systems. Some of these neuro-
hormonal factors, such as the sympathetic nervous system, sex hormones, aldosterone, and
steroids, are discussed elsewhere in this book. In this chapter we present the other main
hormonal systems involved in the maintenance of sodium balance. These systems are
divided into two categories, i.e., the vasoconstrictor and antinatriuretic systems such as the
renin-angiotensin and the endothelin (ET) systems and the vasodilator and natriuretic
systems illustrated by natriuretic peptides and nitric oxide (NO). Because most of these
systems interact with each other to form a complex network enabling the fine tuning of
sodium balance, an integrative view of the renal regulation of sodium balance will be
developed by Montani et al. in Chapter 9.
