Evidence for a new mammalian organ: a preliminary report

During an investigation on the mechanisms by which mannitol increases renal blood flow, using an in vitro perfused rat kidney preparation, it was observed that an osmotic challenge (320 mOsm) was followed by the accumulation of chloride and calcium ions in the renal medulla. Although the chloride was derived from the perfusate, the source of calcium appeared to be localized in the renal sinus fatty tissue. A morphologic study of this area reveals the existence of a tissue complex, having the characteristics of a hitherto unrecognized organ or gland communicating with the renal parenchyma via a portal vascular system. The possible physiologic significance of this complex is discussed.