Case for a renomedullary blood pressure lowering hormone

Ablation of renal tissue makes the subject sensitive to hypertension-inducing mechanisms, especially those due to fluid expansion, either by Na-volume or whole blood. Such hypertensive mechanisms are prevented by deviation of urine flow into a vein. Ablation of the renal medulla, by acute hydronephrosis or chemically, also potentiates the hypertensive state. Transplantation of either the renal medulla or its interstitial cells (RIC) can prevent or reverse hypertension. Under the latter conditions, the protective mechanism appears to result from the secretion of an antihypertensive hormone by the RIC. Lipid extracts of renal medulla not only prevent and reverse the hypertensive state in the same manner as medullary transplants but, under certain conditions, exert an acute depressor effect. The RIC can undergo hyperplastic changes much in the manner of an endocrine structure. For these reasons, it is proposed that the RIC represent an antihypertensive endocrine organ whose putative hormone may be termed the renomedullary antihypertensive hormone (ARH). Additional data in support of these contentions are presented.