Ageing is the main determinant of haemodynamics and autonomic cardiac changes observed in post-menopausal female rats

The aim of this study was to evaluate and compare the effects of early and physiological menopause on cardiac autonomic parameters in aged female rats. To this end, female Wistar rats (22 and 82 weeks old, N=96) were divided into 4 groups: Young Sham-operated Rats, Aged Sham-operated Rats, Young Ovariectomised (OVX) Rats, and Aged OVX Rats. Young Sham-operated and OVX rats were used as controls. The cardiac autonomic parameters were investigated using different approaches: 1) pharmacological evaluation of the autonomic tonus with methylatropine and propranolol; 2) isolated cardiac contractility with β-adrenergic agonists; and 3) quantification of the mRNA and protein level expression of cardiac β-adrenergic receptors. Among the groups of aged female rats, both the Sham-operated and OVX rats showed higher basal mean arterial pressure and heart rate (HR) values compared to their respective young counterparts. The aged groups also showed a predominance of the sympathetic autonomic component in the determination of HR, whereas the young rats showed a vagal predominance. An assessment of cardiac contractility showed that aged Sham-operated and OVX rats had lower contractile responses following the administration of dobutamine compared to their respective young counterparts. In addition, the aged groups showed higher mRNA and protein expression levels of the β1-adrenergic receptors. In conclusion, our results show that haemodynamic alterations and impairment of the autonomic parameters were similar between the groups of rats subjected to early and physiological menopause. Moreover, these results seem to be due to the ageing process and not ovarian hormone deprivation.