A novel natriuretic, hypotensive factor derived from the spleen.

Previous experiments have shown that the reduction in plasma volume observed after administration of atrial natriuretic factor is abolished by splenectomy. In order to determine whether the spleen contains a factor that influences cardiorenal homeostasis, rat spleens were homogenized in phosphate-buffered saline, centrifuged, subjected to ultrafiltration (molecular weight cut-off 10,000), extracted on C18 affinity columns and dried. After reconstitution in isotonic saline, the extract was injected i.v. into conscious rats. In response to this extract, there was a dose-dependent diuresis, natriuresis, kaliuresis and chloruresis which plateaued during the second and third hours following administration. Solute-free water clearance was inversely related to urine output. Blood pressure fell significantly from 109 +/- 3 mm Hg to 103 +/- 3 mm Hg during the first 10 min. after injection of the extract, and tended to remain depressed thereafter. There was no accompanying increase in heart rate. We conclude that the mammalian spleen contains a natriuretic, hypotensive factor that may play a role in cardiorenal homeostasis.