Longitudinal assessment of the effects of oestrogen on blood pressure and cardiovascular autonomic activity in female rats.
1. Published data concerning the effects of ovarian hormones on haemodynamic variability are contradictory. For the first time, the present study used radiotelemetric haemodynamic monitoring to investigate the long-term effects of chronic oestrogen depletion and repletion on cardiovascular autonomic control and arterial baroreflex sensitivity (BRS) in female rats. 2. Blood pressure (BP), heart rate (HR) and +dP/dt(max) of arterial pressure (an estimate of myocardial contractility) were monitored in sham-operated (SO), ovariectomized (OVX) and oestrogen-replaced OVX rats (OVXE2) for 16 weeks. Cardiovascular autonomic control and baroreflexes were assessed by frequency domain analysis of interbeat intervals (IBI) and systolic BP (SBP). 3. Compared with SO rats, OVX rats exhibited no changes in BP, short-lived decreases in HR and sustained reductions in +dP/dt(max) of arterial pressure. The high- (HF; 0.75-3 Hz) and low-frequency (LF; 0.25-0.75 Hz) components of spectral power of IBI were significantly decreased and increased, respectively, by ovariectomy. An increase in the IBI(LF/HF) ratio in OVX rats suggests a shift in the cardiac sympathovagal balance towards sympathetic dominance. Index alpha, the spectral index of spontaneous BRS, was reduced by OVX. 4. Oestrogen replacement caused significant reductions in BP and HR and reversed OVX-induced changes in +dP/dt(max) of arterial pressure and cardiac autonomic activity. The LF oscillations of SBP were reduced in OVXE2 rats, suggesting a reduction in vascular sympathetic tone by oestrogen. 5. These findings highlight the importance of long-term oestrogen therapy in rectifying the detrimental effects of depletion of ovarian hormones on the cardiovascular system and baroreflex.
El-Mas
Mahmoud M
MM
Department of Pharmacology, School of Medicine, East Carolina University, Greenville, North Carolina 27834, USA.
Abdel-Rahman
Abdel A
AA
D000818:Animals; D017776:Autonomic Pathways / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects*; D002319:Cardiovascular System / Q000187:drug effects* / Q000294:innervation*; D004353:Drug Evaluation, Preclinical; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D015914:Estrogen Replacement Therapy; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D008137:Longitudinal Studies; D009200:Myocardial Contraction / Q000187:drug effects; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley
D004343:Drug Implants; D004958:Estradiol