High-salt intake during the growth period elevates blood pressure and alters heart rate variability trajectories in rats

Chronic high-salt intake may exert lasting effects on autonomic regulation across the life course. The growth period is a critical window during which the autonomic nervous system matures, yet how high-salt exposure shapes autonomic maturation remains insufficiently understood. In this study, male Sprague–Dawley rats (5 weeks of age at diet onset) were assigned to a control (0.5% NaCl) or a high-salt (> 4% NaCl) diet for 12 weeks (to 17 weeks of age). Systolic blood pressure (SBP) was measured twice weekly in conscious animals using a tail-cuff system, and heart rate variability (HRV) was derived from electrocardiographic recordings twice weekly under isoflurane anesthesia. Longitudinal changes were modeled using generalized linear mixed models. The high-salt group showed a significant increase in SBP relative to controls (Group × Time, p < 0.001). For frequency-domain HRV, LFnu increased and HFnu decreased significantly over the 12 weeks in the high-salt group, and the between-group differences reached statistical significance (LFnu, p = 0.031; HFnu, p = 0.021). These findings suggest that longitudinal, repeated-measures HRV may serve as a complementary, non-invasive approach for tracking autonomic development, warranting further investigation.