Hypoxia-inducible factor (HIF) regulates expression of genes involved in adaptation to hypoxia and ischemia. Three prolyl hydroxylases (PHD1-3) underlie oxygen-regulated destruction of HIFalpha chains. We have investigated the organ distribution of the PHDs in the rat, their regulation by hypoxia and changes in local expression after experimental myocardial infarction using RNase protection assays, in situ hybridization and immunohistochemistry. mRNAs of all isoforms were detectable in heart, liver, kidney, brain, testis and lung. In normal animals, highest levels for PHD2 mRNA and PHD3 mRNA were found in myocardium, whereas PHD1 mRNA was detected predominantly in the testis. PHD1 mRNA was constitutively expressed. PHD2 mRNA was induced by hypoxia in the liver and PHD3 mRNA in liver, testis and heart. Overall our results show that PHD2 mRNA is ubiquitously expressed in normal animals, in keeping with a general role in oxygen sensing. PHD1 and 3 mRNA distributions suggest particular roles in testis and heart, respectively. In a model of myocardial infarction, in situ hybridization showed periischemic enhancement for PHD2 mRNA and PHD3 mRNA, but not PHD1 mRNA. Immunostaining of PHD2 and 3 in infarcted hearts showed enhanced protein expression, maximal 7 days after infarction. Levels were strongest in regions neighboring areas of HIF staining but also partially overlapped with these zones. Inducibility of PHD2 and 3 by hypoxia and ischemia in vivo has important implications both for the pathophysiology of conditions where oxygen supply is deranged and for attempts to manipulate the HIF system therapeutically.