Relationship of increased plasma atrial natriuretic factor and renal sodium handling during immersion-induced central hypervolemia in normal humans.

Although maneuvers augmenting atrial volume and/or stretch also augment plasma levels of atrial natriuretic factor (ANF), the role of ANF in modulating renal sodium and water handling has not been defined. Water immersion to the neck (NI) was employed to assess the ANF response to acute volume expansion in 13 seated sodium-replete normal subjects. ANF increased promptly and markedly from 7.8 +/- 1.8 to 19.4 +/- 3.8 fmol/ml, then declined to 6.3 +/- 1.4 fmol/ml after 60 min recovery. Concomitantly, NI increased urine flow rate (V) (2.0 +/- 0.6 to 7.0 +/- 0.9 ml/min; P less than 0.001) and sodium excretion (UNaV) (92 +/- 12 to 191 +/- 15 mu eq/min; P less than 0.001), and decreased PRA (-66 +/- 3%) and plasma aldosterone (-57 +/- 6%). Increases of plasma ANF ranged from less than 20% to over 12-fold. Similarly, the natriuretic response to NI varied markedly from none to 500%. There was a strong correlation between peak ANF and peak UNaV (r = 0.67; P less than 0.025), but none between peak V and peak plasma ANF (r = -0.10; P greater than 0.5). These findings suggest that an increase in plasma ANF contributes to the natriuretic response to NI, implying a physiological role for ANF in modulating volume homeostasis in humans.

Increases in circulating atrial natriuretic factor during immersion-induced central hypervolaemia in normal humans.

The role of atrial natriuretic factor (ANF) in modulating volume and circulatory homeostasis remains uncertain, and there has been as yet no systematic analysis of the factors promoting ANF release in humans. Since immersion in water to the neck provides a 'volume stimulus' identical to that induced by 2 litres of saline, without plasma compositional change, immersion to the neck was used to assess the ANF response to acute central blood-volume expansion. Using a radio-immunoassay that reliably detected ANF in human plasma extracts, more than 80% of plasma immunoreactive (ir) ANF was shown to elute as a single peak on reverse-phase high performance liquid chromatography, with a retention time identical to that of the synthetic 28-residue alpha-human (alpha-h) ANF. The response of plasma irANF to 3 h of immersion in water to the neck was evaluated in four sodium-replete normal subjects; the immersion produced a prompt and marked increase in irANF in each subject, and recovery was associated with a prompt return to pre-study levels. Concurrently, there was a marked natriuresis and a profound suppression of plasma renin and aldosterone. These findings support the hypothesis that an increase in plasma ANF contributes to the hormonal and renal effects of immersion in water to the neck, suggesting that ANF has an important physiological role in modulating volume homeostasis in humans.