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Departments of Physiology and Biophysics and Surgery (Cardiothoracic), University of Mississippi Medical Center, Jackson, Mississippi 39216
Recent studies indicate
that baroreflex suppression of renal sympathetic nerve activity is
sustained for up to 5 days of ANG II infusion; however, steady-state
conditions are not associated with ANG II hypertension of this short
duration. Thus the major goal of this study was to determine whether
neurally induced increments in renal excretory function during chronic
intravenous infusion of ANG II are sustained under more chronic
conditions when hypertension is stable and sodium balance is achieved.
Experiments were conducted in five conscious dogs subjected to
unilateral renal denervation and surgical division of the urinary
bladder into hemibladders to allow separate 24-h urine collection from
denervated (Den) and innervated (Inn) kidneys. ANG II was infused after
control measurements for 10 days at a rate of 5 ng · kg
1 · min
1.
Twenty-four-hour control values for mean arterial pressure (MAP) and
the ratio for urinary sodium excretion from Den and Inn kidneys (Den/Inn) were 92 ± 4 mmHg and 0.99 ± 0.05, respectively.
On days 8-10 of ANG II infusion, MAP was stable
(+30 ± 3 mmHg) and sodium balance was achieved. Whereas
equal amounts of sodium were excreted from the kidneys during the
control period, throughout ANG II infusion there was a greater rate of
sodium excretion from Inn vs. Den kidneys (day 10 Den/Inn
sodium = 0.56 ± 0.05), indicating chronic suppression of
renal sympathetic nerve activity. The greater rate of sodium excretion
in Inn vs. Den kidneys during renal sympathoinhibition also revealed a
latent impairment in sodium excretion from Den kidneys. Although the
Den/Inn for sodium and the major metabolites of nitric oxide (NO)
decreased in parallel during ANG II hypertension, the Den/Inn for cGMP,
a second messenger of NO, remained at control levels throughout this
study. This disparity fails to support the notion that a deficiency in
NO production and action in Den kidneys accounts for the impaired
sodium excretion. Most importantly, these results support the
contention that baroreflex suppression of renal sympathetic nerve
activity is sustained during chronic ANG II hypertension, a response
that may play an important role in attenuating the rise in arterial pressure.
baroreflexes; sympathetic nervous system; kidneys; nitric oxide
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