Atrial natriuretic factor and renal function during head-out water immersion in conscious dogs

The potential role of atrial natriuretic factor (ANF) in the renal response to head-out water immersion (WI) was studied. Five female mongrel dogs, trained to stand for 100 min in air followed by 100 min of thermoneutral WI at 37° C or 200 min in air (timed control, TC), were chronically instrumented with arterial and venous catheters. The animals were hydrated with a volume of 0.45% NaCl solution equivalent to 2% of their body weight. Prehydration levels of arterial ANF were 243 ± 15 (SE), and venous ANF levels were 211 ± 21 pg/ml. WI resulted in an increase in urine flow from 0.7 ± 0.1 ml/min to a peak flow of 2.2 ± 0.3 ml/min (P < 0.05). On immersion, plasma venous and arterial ANF levels increased significantly by 29 and 21% from the preimmersion values of 183 ± 14 and 222 ± 20 pg/ml, respectively. The arterial-venous difference for plasma ANF was maintained at 35 ± 14 pg/ml (P < 0.05) during WI; therefore venous sampling may suffice as a measure of circulating ANF levels. Sodium excretion increased linearly during WI to a peak value of 228 ± 32 μeq/min from a base line of 52 ± 12 μeq/min (P < 0.05). These data indicate that peripheral tissues extract ANF and that WI is a physiological stimulus for the release of ANF. However, the time course and magnitude of the changes in plasma ANF and urine sodium excretion during WI are not comparable, and other mechanisms are likely responsible for the WI natriuresis. Since plasma electrolytes and osmolality did not change in WI, it is likely that a direct hemodynamic effect causes the release of ANF from the atria.