Impact of gonadectomy on sympatho-vagal balance in male and female normotensive rat

Abstract

OBJECTIVE: It is well established that autonomic nervous system and sympatho-vagal balance plays an important role in maintaining arterial blood pressure (ABP) (Salman IM., 2016) and that autonomic regulation of ABP differs between males and females (Hart EC et al., 2014). We hypothesised that sex hormones affect blood pressure via the autonomic nervous system and that the late development of hypertension in females is due to protective effects of ovarian steroids in females rather than due to detrimental effects of testosterone in males. DESIGN AND METHOD: We used adult, 12 months old, Wistar female and male, intact and gonadectomised rats (n = 8, per each group). Resting ABP was recorded by radio-telemetry. Heart rate (HR) and ABP variability were calculated using Spike2 software. Effect of gender and gonadectomy were assessed by two-way Anova. RESULTS: Females had lower systolic (S)BP compared to males (121 ± 1 vs 128 ± 2 mmHg; P < 0.05). Intact (81 ± 2 mmHg) but not ovariectomised (89 ± 2 mmHg) females had lower diastolic (D)BP compared to males (91 ± 1 mmHg; P < 0.01). Moreover, intact (353 ± 6bpm) but not ovariectomised (307 ± 5 bpm) females had higher HR compared to males (353 ± 6bpm; P < 0.001). However, ovariectomy did not influence the higher respiratory rate in females vs males (91 ± 3 vs 78 ± 3 bpm; P < 0.001).Power spectra analysis of SBP shows that males (22.4 ± 3) and ovariectomised females (26.9 ± 3) had lower High Frequency percentage vs females (38 ± 3; P < 0.05) suggesting that female hormones affect ABP by modulating the parasympathetic activity. The Very Low Frequency percentage was higher in males vs females (40 ± 4 vs 28 ± 4; P < 0.05) suggesting that sympathetic vasomotor tone might play an important role in the differential regulation of SBP between males and females. CONCLUSIONS: Altogether, this results show that female hormones have a positive effect on ABP and that they affect ABP via modulating parasympathetic activity. Further analyses of BP and HR variability at different ages are needed to determine the interaction between age, BP and gender.