Figure 174

Expression of messenger RNA (mRNA) for prepro-epidermal growth factor (EGF) in kidney. This schematic depicts the localization of mRNA for prepro-EGF under basal states in kidney. Prepro-EGF mRNA is localized to the medullary thick ascending limbs (MTAL) and distal convoluted tubules (DCT). Immunohistochemical studies demonstrate that under basal conditions the peptide is located on the luminal membrane with the active peptide actually residing within the tubule lumen. It is speculated that, during pathologic states, preformed EGF is either transported or routed to the basolateral membrane or can enter the interstitium via backleak. After a toxic or ischemic insult, expression of EGF is rapidly suppressed and can remain low for a long time. Likewise, total renal content and renal excretion of EGF decreases. CTAL—cortical thick ascending limb; IMCD—inner medullary collecting duct; OMCD—outer medullary collecting duct; and PCT—proximal convoluted tubule.

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