Age-dependent differences in the effect of atrial natriuretic factor.

Replacement of drinking water by 1.8% NaCl solution produces a severe hypernatremia in prepubertal rats and only a moderate elevation of the plasma sodium concentration (pNa) in adults. Hypernatremia in prepubertal rats was reduced by infusion of blood from adult rats, whereas blood from young rats was without this effect. The aim of this study was to find out if the natriuretic factor containing atrial extracts from prepubertal (AEP) and adult (AEA) rats also differ in their ability to reduce hypernatremia in prepubertal rats. A decrease of pNa was observed 10 min after the administration of AEA (delta = -5.43 mmol/l). AEP failed to show this effect (delta = +0.92 mmol/l). No significant effect of AEA on pNa was observed in adult rats with moderate hypernatremia (delta = -1.88 mmol/l). Natriuretic and diuretic effects of AEP were also significantly lower than those of AEA if they were tested in prepubertal recipients, whereas no difference in activities of AEP and AEA was found in adult recipients. Possible mechanisms of the hypernatremia suppressing activity of AEA, causes of the differences in activities between AEA and AEP, and consequences of the low AEP activity for prepubertal rats are discussed.