Sympathetic nervous system (SNS) hyperactivity, or increased sympathetic tone, is also common in women with PCOS, despite most patients being unaware of it. Hyperactivity of the SNS is associated with elevated serum androgen levels, anovulation, and menstrual irregularity, and may play a role in the pathogenesis of the disorder.
14-18 Systemic SNS hyperactivity has been reported as elevated resting heart rate (HR), decreased heart rate variability (HRV), hypertension, exaggerated systolic blood pressure response to exercise and attenuated heart rate recovery (HRR) after exercise, increased muscle sympathetic nerve activity, and increased levels of adrenergic metabolites in the serum and urine.
19-21 Chronic SNS hyperactivity is associated with visceral adiposity, and obesity further exacerbates SNS hyperactivity.
22-25 Studies of both women with PCOS and animal models have demonstrated locally increased sympathetic tone, including increased ovarian sympathetic outflow and expression of nerve growth factor, increased sympathetic tone of adipose tissue, and altered expression of adrenoreceptors in the hypothalamus, periventricular nucleus, and ovaries.
18,26-30 In a previous study, we demonstrated that women with PCOS exhibit signs of increased sympathetic tone that can be assessed both by physiologic and osteopathic measures, with osteopathic structural examination identified as a valuable means to detect sympathetic hyperactivity in women with PCOS even before the physiologic signs manifest.
2 In addition, studies in a rat model of PCOS have shown that transection of either the superior ovarian nerve or the vagus nerve improved sympathetic tone, decreased ovarian androgen production, improved reproductive cyclicity, and restored ovulation.
26,31 Together, these findings underscore a role for the SNS in the pathogenesis and presentation of PCOS, particularly the androgenic and reproductive features.