Sustained depressor effect of renal medullary extract in the normotensive rat

• In addition to its "well-known pressor ac-tivities, the normal kidney has long been suspected of possessing an antihypertensive endocrine function responsible for its "pro-tective " effect in various forms of experimen-tal hypertension. However, the localization and nature of this effect have proven elusive. The demonstration by Braun-Menendez and von Euler,1 and Grollman and his co-workers2 that hypertension develops in the bilaterally nephrectoniized auimal renewed interest in the possibility that certain forms of hyper-tension may represent a relative deficiency of a physiologically active depressor material. The observation that hypertension does not develop in the severely ureinic animal with uretero-caval anastomosis'3 suggested that the normotensive state of these animals was related to a nonexcretory renal metabolic function. Investigations by Muirhead and his colleagues have implicated the renal medulla as the source of antihypertensive activity, since explants and extracts of medulla appear to prevent the development of renoprival hy-pertension to a degree comparable with whole kidney explants' ' or homogenous renal trans-plants. On the other hand, Sokabe and Groll-man, on the basis of the effects of medullec-tomy and corticectomy, have concluded that the maintenance of normotension resides in kidney cortex and not medulla. In an attempt to investigate the properties of the antihypertensive principle, Hamilton and Grollman8 have prepared a dialyzable