Atrial Natriuretic Factor
Mammalian atrial myocytes contain specific granules that store a powerful rapidly acting natriuretic/diuretic factor, which is referred to as the atrial natriuretic factor (ANF). So far, ANF has been found in atrial extracts from rat, rabbit, dog, baboon and man. Injection of partially purified rat ANF into rats results in up to a 50-fold increase in urinary sodium chloride excretion within 10 minutes. The effect of ANF appears to be caused by inhibition of sodium chloride reabsorption in the ascending limb of Henley’s loop or in the medullary collecting duct; although, alterations in intrarenal hemodynamics may also participate. The exact mechanism by which ANF alters renal tubular transport is unknown, but the substance does not appear to inhibit sodium-potassium ATPase. ANF does not act through release of a substance from the brain, does not require the intact nervous system for its action and is active in the isolated kidney. Biochemical studies suggest that ANF consists of one or more peptides with molecular weights of 4,000–6,000 daltons. It is also probable that one or more larger molecular species of ANF exist. Currently, the most reliable method for measuring ANF activity is to inject unknown test substances into anesthetized rats and determine the effect on renal sodium excretion. It is not known whether the atrial natriuretic factor is released into the blood stream, and thus its physiological relevance has not been determined. Elucidating the chemical structure of this powerful endogenous natriuretic substance and understanding its mechanism of action in the kidney may lead to the development of new specific diuretic drugs for treating millions of patients with hypertension and heart failure.
KeywordsAtrial Natriuretic Factor Atrial Myocytes Specific Granule Natriuretic Response Renal Sodium Excretion
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