Sex Differences in Exercise-Induced Arteriolar Remodeling of Skeletal Muscle

Chronic exercise induces functional adaptations in skeletal muscle microcirculation, but whether these are accompanied by sex-specific histological remodeling of arterioles remains unclear. This study examined gracilis muscle arterioles in trained (Ex) and sedentary (Se) female (F) and male (M) Wistar rats after a 12-week intensive swimming program (Mex = 6, FEx = 6; MSed = 6, FSed = 5). Histological remodeling was assessed by quantitative colorimetry analysis of resorcin-fuchsin (elastica; n = 661) and SMA-DAB (smooth muscle actin; n = 692) staining, focusing on elastic fiber density, internal elastic lamina (IEL) characteristics, and smooth muscle density in intramuscular and intermuscular vessels. Elastic fiber density and IEL thickness were generally greater in female animals than in males (p < 0.05). IEL staining intensity showed significant effects of sex (p = 0.043), exercise (p = 0.021), and a significant sex-by-exercise interaction (p = 0.037), with exercised females exhibiting the highest IEL staining intensity. Smooth muscle density did not differ significantly by sex or training status, although it was higher in intermuscular than intramuscular arterioles (p < 0.001), and increased with vessel diameter primarily in the intermuscular group. These findings demonstrate exercise-induced, sex-specific histological remodeling of skeletal muscle arterioles, primarily affecting elastic components, with more pronounced elastic adaptation in females.