Endothelial and neuronal nitric oxide synthases variably modulate the oestrogen-mediated control of blood pressure and cardiovascular autonomic control.
1. We have shown previously that long-term oestrogen (E2) replacement lowers blood pressure (BP) and improves cardiovascular autonomic control in ovariectomized (OVX) rats. In the present study, we investigated whether constitutive and/or inducible (i) nitric oxide synthase (NOS) modulate these E2 effects. 2. We evaluated changes in BP, myocardial contractility index (dP/dtmax ) and power spectral indices of haemodynamic variability following selective inhibition of endothelial (e) NOS with N(5)-(1-iminoethyl)-L-ornithine (L-NIO), neuronal (n) NOS with N(ω)-propyl-L-arginine (NPLA) or iNOS with 1400W in telemetered OVX rats treated for 16 weeks with (OVXE2) or without (control; OVXC) E2. 3. The OVXE2 rats exhibited: (i) reduced BP and increased dP/dtmax ; (ii) cardiac parasympathetic dominance, as reflected by the reduced low-frequency (LF; 0.25-0.75 Hz)/high-frequency (HF; 0.75-3 Hz) ratio of interbeat intervals (IBI(LF/HF)); and (iii) reduced LF oscillations of systolic BP, suggesting a reduced vasomotor sympathetic tone. Inhibition of eNOS (L-NIO; 20 mg/kg, i.p.) elicited a shorter-lived pressor response in OVXE2 than OVXC, rats along with reductions in dP/dtmax and increases in the spectral index of spontaneous baroreflex sensitivity (index α). Treatment with 1 mg/kg, i.p., NPLA reduced BP and increased the IBI(LF/HF) ratio in OVXE2 but not OVXC rats. The iNOS inhibitor 1400W (5 mg/kg, i.p.) caused no haemodynamic changes in OVXC or OVXE2 rats. 4. Overall, constitutive NOS isoforms exert restraining tonic modulatory BP effects that encompass eNOS-mediated reductions and nNOS-mediated elevations in BP in OVXE2 rats. Baroreflex facilitation and dP/dtmax reductions may account for the shorter pressor action of L-NIO in E2-treated, compared with untreated, OVX rats.
Department of Pharmacology and Toxicology, School of Medicine, East Carolina University, Greenville, NC, USA.
Mahmoud M
MM
El-Mas
Abdel A
AA
Abdel-Rahman
D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects*; D002319:Cardiovascular System / Q000187:drug effects* / Q000378:metabolism; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D008969:Molecular Sequence Data; D009200:Myocardial Contraction / Q000187:drug effects; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D004967:Estrogens; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat
blood pressure; cardiac autonomic control; nitric oxide synthases; oestrogen; ovariectomy; spontaneous baroreflex sensitivity