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-estradiol on sympathetic activity and pressor
response to phenylephrine in ovariectomized rats
Department of Physiology and Biophysics, University of Tennessee, Memphis, Tennessee 38163
The effects of 17
-estradiol
(E2) on sympathetic activity
were examined in conscious unrestrained ovariectomized rats,
instrumented under methohexital anesthesia to record mean arterial
pressure (MABP), heart rate (HR), renal nerve activity (RNA), and
splanchnic nerve activity (SNA) 1 day before the experiment. Injection
of E2 (150 µg/kg iv) caused
reductions (P < 0.01) in RNA (29 ± 6%), SNA (25 ± 2%), and HR (26 ± 5 beats/min) within 20 min, but MABP remained unchanged. Ninety minutes after intravenous
injection of E2 or vehicle,
intravenous infusion of phenylephrine (PE; 6.2 µg · min
1 · kg
1)
induced similar increases in MABP and decreases in HR, RNA, and SNA in
both groups. By contrast, in rats chronically treated with
E2, the pressor response to PE was
smaller (P < 0.01; 22 ± 5 mmHg)
than in vehicle-treated rats (40 ± 4 mmHg). The changes in HR, RNA,
and SNA were similar in both groups, but the ratios of changes in HR
and SNA to MABP, an index of baroreflex sensitivity, were greater in
the E2-treated rats. These
findings suggest that E2 can act
centrally to modulate sympathetic function and thereby participate in
cardiovascular regulation.
blood pressure; renal nerve; splanchnic nerve; baroreflex
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