Factors that regulate extrarenal erythropoietin production.

Extrarenal sites are the major source of erythropoietin (Ep) production in fetuses and neonates. Afterwards, however, the kidneys are the major site. The most likely site of Ep production is the liver, although attempts to extract Ep from the liver have been, to date, unsuccessful. Extrarenal Ep production, as is the case for renal Ep production, is regulated primarily by the oxygen demand: supply. However, some differences have been identified in the response of extrarenal and renal sites of Ep production to several conditions. Two classes of conditions that selectively influence extrarenal Ep production are the subject of this paper. These are the following: 1) factors that cause reparable hepatic injury--including partial hepatectomy, CC14, and bile duct ligation, and 2) continuous perfusion of angiotensin II. The differences between the mechanism by which these two factors influence extrarenal Ep production will be explored and discussed.