Abstract Body: Changes in chromatin conformation caused by common genetic variations may impact blood pressure regulation and hypertension risk. A major function of CCCTCF-binding factor (CTCF) is to bind to DNA to regulate and maintain chromatin conformation, and thereby gene expression. Cellular expression of CTCF is critical for proper Renin expression and the Renin gene is surrounded by multiple CTCF-binding motifs. In the Dahl salt-sensitive (SS) rat, CRISPR-Cas9 was utilized to create three models harboring mutations to the CTCF motif surrounding the Renin gene. CTCF binding was confirmed to be disrupted in all three models. The mutants and wild-type (WT) littermates were then placed on a 0.1%, 4.0% or maintained on a 0.4% NaCl diet for four days, and Renin mRNA and plasma renin activity (PRA) was examined. mRNA analysis showed no differences in Renin expression on any diet for any model compared to WT. Interestingly, two of our male mutant models failed to increase their PRA on the 0.1% NaCl diet (CTCF1=13.87±0.86; CTCF2=13.95±0.59; p<0.05 compared to WT=17.52±0.81 on 0.1% NaCl). We hypothesized that Renin dynamic transcriptional response to salt depletion is delayed in the mutant models compared to WT. To test this, we have utilized an ex vivo kidney slice culture approach. Kidneys were excised from SS rats fed a 4.0% NaCl diet for 1-2 days, sliced to ~1-3 mms, and cultured for 24 hrs. Renin expression was evaluated at 0, 1, 2, 4, 8, 12, 16, 20 and 24 hrs of incubation in basal media. Renin expression was elevated in SS rats at 8 hrs (3.82±0.38 compared to 0 hr = 0.93±0.32) and continued to increase until 12 hrs (7.05±1.87) and reduced at 16 hrs (1.42±0.70). CTCF1 mutant Renin expression was significantly reduced at 12 hrs (3.77±0.58 compared to WT=7.05±1.87), while CTCF2 mutants showed no differences in Renin expression compared to WT. Thus, we established an ex vivo approach for monitoring the dynamic changes in Renin expression by culturing kidney slices. This method could be used to evaluate other stimuli, such as therapeutics.