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1 Department of Physiology and Biophysics, University of Sao Paulo, Sao Paulo, SP, Brazil
2 Department of Pharmacology and Toxicology, Wright State University, Dayton, OH, USA
3 Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, PA, USA
* To whom correspondence should be addressed. E-mail: mariana.morris{at}wright.edu.
Oxytocin (OT) has been implicated in the cardiovascular responses to exercise, stress and baroreflex adjustments. Studies were conducted to determine the effect of genetic manipulation of the OT gene on blood pressure (BP), heart rate (HR) and autonomic/baroreflex function. OT knockout (OTKO-/-) and Control +/+ mice were prepared with chronic arterial catheters. OTKO-/- exhibited a mild hypotension (102±3 vs 110±3 mmHg). Sympathetic and vagal tone were tested using B1 adrenergic and cholinergic blockade (atenolol and atropine). Magnitude of sympathetic and vagal tone to the heart and periphery were not significantly different between groups. However, there was an upward shift of sympathetic tone to higher HR values in OTKO-/-. This displacement combined with unchanged basal HR led to larger responses to cholinergic blockade (+77 ±25 vs +5±15 bpm, OTKO-/-vs Control+/+). There was also an increase in baroreflex gain (-13.1±2.5 vs -4.1±1.2 bpm/mmHg, OTKO-/- vs Control+/+), over a smaller BP range. Results show that OTKO-/- are characterized by 1) hypotension, suggesting that OT is involved in tonic blood pressure maintenance 2) enhanced baroreflex gain over a small BP range, suggesting that OT extends the functional range of arterial baroreceptor reflex 3) shift in autonomic balance, indicating that OT reduces the sympathetic reserve.
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