Partially Purified Human and Rat

SUMMARY Specific granules of rat atrial myocytes contain a potent fast-acting atrial natriuretic factor (ANF) and have been observed in all mammalian atria thus far examined. In this study, using a rat assay we found ANF in rat, rabbit, dog, baboon, and man. The ANF's from these species induced the characteristic diuresis and natriuresis of rapid onset and decay. The human and rat ANF's were acid-extractable, heat-resistant, and trypsin-sensitive, suggesting that both are peptides. When frac-tionated on Sephadex G-75, ANF eluted at approximately 1.4 to 2.9 elution volume/void volume. The human and rat ANF dose-response relationships showed that changes in urinary sodium excretion (AUNiV) were linearly related to log mg protein injected per kg rat assay weight (r2 = 0.9853 and 0.9966, respectively). The minimum and maximum responses to rat ANF on the average were 14 ± 3 and 409 ± 5 1 /xEq Na/kg-10 min ( ± SE) respectively. The AUN.V of rats given a second injection of ANF was not altered by a first injection. Furosemide induced a similar but slightly longer diuretic, natriuretic, and kaliuretic response pattern than that of ANF. Nevertheless, a classical four-point log dose-response analysis revealed that under certain conditions furosemide could be a suitable standard against which the potencies of unknown preparations of ANF can be compared. The relative potency of the partially purified rat ANF used in this study was 0.654 mg furosemide/mg protein (95