Partial Chemical Characterization of a Natriuretic Substance in Rat Atrial Heart Tissue

Abstract

Extracts of atrial and ventricular rat heart tissue were prepared in phosphate-buffered saline and boiled (PBS-boiled), or in acetic acid and fractionated using Sephadex G-75. The extracts were injected i.v. into anesthetized nondiuretic (i.e., not hydrated) rats to assay for natriuretic activity. PBS-boiled atrial extract caused urinary Na excretion (UNaV) to increase significantly (P < 0.05) by 672 .+-. 307% (.+-. SE) during the 10 min after injection, while no significant change in UNaV occurred after injection of PBS alone or ventricular extract. UKV and urine volume increased significantly by 400 .+-. 236% and 499 .+-. 105%, respectively, after injection of PBS-boiled atrial extract. Pooled active fractions from Sephadex G-75 of acid atrial extract (lyophilized and reconstituted in PBS) caused UNaV and urine volume to increase significantly by 1015 .+-. 401% and 807 .+-. 291%, respectively, and a smaller but significant increase in UKV of 158 .+-. 23%. The natriuretic activity of acid atrial extract eluted in the MW range of 3600 to 44,000 daltons was unaffected by heating in a boiling water bath, treatment with concanavalin A, incubation with plasma or removing the head of the assay rat, but was abolished by treatment with trypsin. These properties do not generally resemble those of the natriuretic factors in blood and urine previously reported.