Natriuretic hormones, sodium regulation

At least three other groups of factors believed to regulate sodium secretion are neurogenic factors, switches from salt-conserving to salt-wasting nephrons, and natriuretic hormones. When dietary sodium is low, renal excretion decreases within 4 days to levels approaching zero. Reduced renal excretion results in part from aldosterone production. However, a decrease in urinary sodium has been observed with normal levels of aldosterone secretion. Consequently,... 

In reviewing the various hypotheses about regulation of sodium metabolism. Mills [28] proposed that renal sodium excretion depends on a pressure-sensitive mechanism near the juxtaglomerular cells that releases an active natriuretic hormone promptly when the site is stimulated by an increase in pressure. Conversely, sodium retention is believed to be caused by a decrease in this substance, by a fall in glomerular filtration rate, and by the release of renin to increased aldosterone production [29, 30]. 

Nevertheless, claims of partial purification of the natriuretic hormone are not definitive. Moreover, well-known hormones, such as calcitonin and a-NSH, could also be responsible for the natriuretic effect. It is questionable that either of these hormones plays a considerable role in regulating sodium metabolism. Hormone responses to sodium loads and losses are summarized in Fig. 9-9, and the hypothetical role of the natriuretic hormone is illustrated in Fig. 9-10. 

Hypernatremia is not an absolute finding in primary hyperaldosteronism, and a mechanism of renal adaptation has been proposed. Thus, in progressive aldosteronism, salt retention activates a nonaldoste-ronic mechanism of sodium regulation, which increases sodium excretion in the distal tubules without affecting the proximal tubule, thus reestablishing the balance between sodium intake and excretion. Whether the postulated natriuretic hormone [32] is involved remains to be seen (see Fig. 9-12). 

Atrial natriuretic peptide Atrial natriuretic peptide is a polypeptide hormone predominantly secreted by the cardiocytes of the right atrium of the heart. It increases urinary. sodium excretion. The physiological role, if any, of this hormone is unclear, but it probably only plays a minor role in the regulation of ECF volume and sodium concentration. To date no disease slate can be attributed to a primary disorder in the secretion of atrial natriuretic peptide. 

Sodium (Na ) Aldosterone Antidiuretic hormone (ADH)—water regulation Atrial natriuretic peptide (ANP) Renal reabsorption Renal excretion... 

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