Prostaglandin F-2 alpha (PGF(2 alpha)), modulates hepatocyte functions via a heptahelical G(q)-coupled PGF(2 alpha)-receptor (FP-R) which in liver is expressed exclusively in hepatocytes. The aim of the present study was to isolate the 5'-flanking region of the rat FP-R gene and to elucidate its basal and IL-6-modulated transcription control function in rat hepatocytes. The 5'-nontranslated region of the rat hepatocyte FP-R mRNA differed from the corresponding region in rat fetal astrocyte or corpus luteum. It was encoded by exons la and 2 which were separated by a 1.4 kb intron containing the exons Ib and Ic coding for the 5'-untranslated region of rat fetal astrocyte and corpus luteum FP-R mRNA, respectively. The transcription initiation site in hepatocytes was localized 263 bp upstream of the start ATG by 5'-RACE. A DNA-fragment covering the 5'-flanking region of the rFP-R gene from -1 of the transcription initiation site to -2590 bp was cloned and sequenced. Its 3'-two thirds had a 65% sequence identity to the mouse FP-R promoter however no homology to the bovine FP-R promoter. In the overlapping sequence most of the putative transcription factor binding sites were conserved between mouse and rat. The rat promoter contained no classical TATA- or CAAT-boxes but putative binding sites for the transcription factors C/EBP, GATA-1, HNF-1, HNF-3 beta, SP-1, and USF. Luciferase reporter gene constructs containing portions of the 5'-flanking region were transfected into rat hepatocytes. Luciferase expression ranked -181 greater than or equal to -608 < -1418 > -1821 greater than or equal to -2590. The strongest transcriptional activity was conferred by the region between -608 and -1418 containing a cluster of potential HNF-1 and HNF-3 beta binding sites that might allow the exclusive expression of FP-R mRNA in hepatocytes. The amount of FP-R mRNA and the luciferase expression under control of the -2590 promoter fragment were reduced by IL-6 in hepatocytes.