Citrulline Supplementation Improves Aortic Vasodilation and Prevents Aortic Thickening Only in Female Rats

BACKGROUND: Aging is associated with endothelial dysfunction and vascular remodeling, partly due to reduced nitric oxide (NO) bioavailability. l-citrulline, a precursor of l-arginine and NO synthesis, has been proposed as a therapeutic strategy to improve vascular function. This study evaluated the effects of chronic citrulline supplementation on aortic structure and vasodilatory function in adult male and female rats. METHODS: Eight-month-old male and female Sprague-Dawley rats were randomly assigned to control or treatment groups. The treated animals received oral malate citrulline (1 g/kg/d) for 12 weeks. We isolated thoracic aortas for histological and morphometric analyses, including tunica media thickness and intima/media ratio. We assessed vascular reactivity in vitro using isolated aortic rings in an organ bath system, measuring acetylcholine (ACh)-induced relaxation following phenylephrine-induced contraction. RESULTS: < .05. No differences in vasorelaxation were observed in males between the treated and control groups. Histological analyses showed that treated females had less disruption of elastic fibers and a thinner minimal intima than controls, whereas males showed no structural differences. CONCLUSIONS: Citrulline supplementation improves endothelium-dependent vasodilation and may preserve aortic structural integrity in female rats but not in males. These findings suggest a sex-dependent vascular response to citrulline, potentially mediated by differences in NO signaling and hormonal regulation. Citrulline may represent a therapeutic strategy to improve vascular function during aging, particularly in females. CLINICAL IMPACT: The findings may guide clinical trials investigating how hormonal status and nitric oxide signaling affect the efficacy of citrulline supplementation in female patients. Ultimately, these insights could establish citrulline as a targeted, preventive intervention to preserve aortic structural integrity and reduce cardiovascular disease risk in the aging female population.