A NOVEL NATRIURETIC, HYPOTENSIVE FACTOR DERIVED FROM THE SPLEEN

Previous experiments have shown that the reduction in plasma volume ob served after administration of atrial natriuretic factor is abolished by splenectomy. In order to determine whether the spleen contains a fa ctor that influences cardiorenal homeostasis, rat spleens were homogen ized in phosphate-buffered saline, centrifuged, subjected to ultrafilt ration (molecular weight cut-off 10,000), extracted on C-18 affinity c olumns and dried. After reconstitution in isotonic saline, the extract was injected I.V. into conscious rats. In response to this extract, t here was a dose-dependent diuresis, natriuresis, kaliuresis and chloru resis which plateaued during the second and third hours following admi nistration. 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 i ncrease in heart rate. We conclude that the mammalian spleen contains a natriuretic, hypotensive factor that may play a role in cardiorenal homeostasis.