Sex-dependent expression of seven housekeeping genes in rat liver

Background and Aim: Sexual differences in the transcript levels of various genes including the hepatic isoforms of cytochrome P450 have been extensively studied. Expression of these sexual dimorphic genes have been quantified by Northern blotting, nuclear run on assays and reverse transcriptase‐polymerase chain reaction (RT‐PCR) methods using numerous housekeeping genes to normalize results. Earlier reports apparently assumed that these internal controls were sex‐independent. We have studied sex differences in the expression levels of seven different commonly used housekeeping genes. Method: We have used quantitative and semiquantitative RT‐PCR to monitor the levels of hepatic mRNAs in intact and hypophysectomized male and female rats. Results: We have observed sex‐dependent expression of the commonly used housekeeping genes tubulin, cyclophilin, tyrosine aminotransferase, β‐actin, glyceraldehyde‐3‐phosphate dehydrogenase, 18S and one unconventional housekeeping gene, that is, hypoxia inducing factor‐1α, in the livers of intact male and female rats. With the exception of glyceraldehyde‐3‐phosphate dehydrogenase and 18S which were female‐predominant (P