Angiotensin II (Ang II) plays important roles in cardiac extracellular matrix remodeling via its type 1A receptor (AT_1A). The cytokines tumor necrosis factor- and interleukin-1 (IL-1) were shown previously to upregulate AT_1A mRNA and protein, thereby increasing the profibrotic response to Ang II in cardiac fibroblasts. The present experiments implicate increased nuclear factor-B (NF-B)-dependent transcription and also, to a lesser extent, altered mRNA splicing in the mechanism of receptor upregulation. Cytokine stimulation was found to increase AT_1A heterogeneous nuclear RNA (hnRNA) levels, strongly suggesting that mRNA upregulation occurred transcriptionally. The transcription factor, NF-B, was previously deemed necessary for cytokine induced AT_1A mRNA upregulation. Computer analysis of upstream DNA sequences revealed putative NF-B elements at -365 and -2540 bp. Both isolated elements were shown to bind NF-B using gel-shift assays and to transactivate a minimal promoter using reporter assays, although -365 appeared stronger. Three splice variants of AT_1A mRNA that have different 5' untranslated regions (UTRs) were detected in rat tissues, namely exon1-2-3 (predominant), exon1-2-3+6 and exon1-3. Cytokine treatment of fibroblasts upregulated all splice variants, but exon1-3 increased more than the others. This differential upregulation, albeit of modest magnitude, was statistically significant with IL-1 treatment. Exon 2 contains an inhibitory minicistron and a predicted inhibitory hairpin structure. Luciferase reporter assays indicated that each splice variant translates at a different efficiency, with exon1-2-3+6 (both minicistron and hairpin) < exon1-2-3 (minicistron only) < exon1-3 (neither). These results provide evidence that cytokines increase AT₁ protein levels by altering both transcription and splicing.