The objective of this study was to determine whether and how growth hormone (GH) regulates hepatic expression of GH receptor (GHR) mRNA in cattle. Ribonuclease protection assays revealed that injection of GH in a slow-release formula increased both hepatic GHR and insulin-like growth factor I (IGF-I) mRNAs one week after the injection. The increases in GHR and IGF-I mRNAs were highly correlated. Western blot analysis showed that the injection also increased liver GHR protein level. In cattle and other mammals, hepatic GHR mRNA is expressed as variants that differ in the 5'-untranslated region, due to the use of different promoters in transcription and/or alternative splicing. We found that GH increased the expression of the liver-specific GHR mRNA variant, GHR1A, without affecting the other two major GHR mRNA variants in the bovine liver, GHR1B and GHR1C. In transient transfection analyses, GH could robustly activate reporter gene expression from a 2.7 kb GHR1A promoter, suggesting that GH augmentation of GHR1A mRNA expression in the liver is at least partially mediated at the transcriptional level. Further transfection analyses of serially 5'-truncated fragments of this promoter narrowed the GH-responsive sequence element down to a 210 bp region that contained a putative signal transducer and activator of transcription 5 (STAT5) binding site. Electrophoretic mobility shift assays demonstrated that this putative STAT5 binding site was able to bind to STAT5b protein. In cotransfection assays, deletion of this putative STAT5 binding site abolished most of the GH response of the GHR1A promoter. Like one week GH action, six hours (i.e., short-term) GH action also increased liver expression of GHR1A and total GHR mRNAs in cattle. These observations together suggest that GH directly stimulates the expression of one GHR mRNA variant, GHR1A, through binding STAT5 to its promoter, thereby increasing GHR mRNA and protein expression in the bovine liver.