Abstract Body: Hypertension impacts half of US adults and importantly is more prevalent in men than premenopausal women. Sex hormones, particularly estrogen, have been implicated in this sex-difference. Recently we showed renal medullary estrogenic signaling via the G protein-coupled estrogen receptor 1 promotes sodium excretion in female, but not male, Sprague Dawley (SD) rats which implicates estrogen as a possible female-specific natriuretic factor. This led us to question whether the kidney could produce its own steroids, including estrogen, to respond to salt load changes locally. Evidence in cultured COS-7 and fetal kidney cells indicates the expression and activity of steroidogenic enzymes. Recently, we showed the outer medulla of the female SD rat kidney expresses key enzymes and metabolites involved in sex steroid biosynthesis. It is unknown how ovarian estrogen regulates steroidogenesis in the kidney. We hypothesize that ovarian estrogen stimulates the intrarenal capacity to biosynthesize sex steroids. To test this, we measured mRNA expression of several steroidogenic enzymes in the renal outer medulla of gonadally-intact female or ovariectomized SD rats (N=6). Cholesterol is the initial substrate for steroid synthesis. Thus, we first measured HMG-CoA reductase (HMGCR), the key synthesizing enzyme for cholesterol and steroidogenic acute regulatory protein (StAR), which helps commit cholesterol to steroid synthesis. Ovariectomy (OVX) reduced mRNA expression of both when compared to intact females (HMGCR: 63.5 ± 6.2 vs 100.0 ± 10.7 P=0.0169; StAR: 66.6 ± 12.4 vs 100.0 ± 6.4 P=0.0298). Although not significantly different, OVX seemed to reduce the expression of hydroxysteroid 3-β Dehydrogenase, which converts several intermediate steps in androgen and estrogen synthesis, compared to intact females (73.4 ± 13.3 vs 100.0 ± 9.7 P=0.1283). Hydroxysteroid 17-β Dehydrogenase (17β-HSD) 1, which converts estrone to estradiol, was unchanged in OVX compared to intact females (107.6 ± 13.2 vs 100.0 ± 10.1 P=0.6537). OVX reduced expression of 17β-HSD2 (28.34 ± 7.8 vs 100.0 ± 12.85 P=0.0008) and 17β-HSD3 (71.1 ± 7.5 vs 100.0 ± 5.7 P=0.0097) which interconvert androstenedione and testosterone compared to intact females. Combined these data suggest that ovariectomy blunts the intrarenal machinery for steroidogenesis. Additional experiments are required to test whether menopause downregulates renal sex steroid biosynthesis and predisposes postmenopausal women to hypertension.