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Departments of Physiology and Biophysics and Surgery (Cardiothoracic), University of Mississippi Medical Center, Jackson, Mississippi 39216
Recent studies indicate that renal
sympathetic nerve activity is chronically suppressed during ANG II
hypertension. To determine whether cardiopulmonary reflexes and/or
arterial baroreflexes mediate this chronic renal sympathoinhibition,
experiments were conducted in 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. Dogs were studied 1)
intact, 2) after thoracic vagal stripping to eliminate
afferents from cardiopulmonary and aortic receptors [cardiopulmonary
denervation (CPD)], and 3) after subsequent denervation of
the carotid sinuses to achieve CPD plus complete sinoaortic denervation
(CPD + SAD). After control measurements, ANG II was infused for 5 days
at a rate of 5 ng · kg
1 · min
1. In the
intact state, 24-h control values for mean arterial pressure (MAP) and
the ratio for urinary sodium excretion from Den and Inn kidneys
(Den/Inn) were 98 ± 4 mmHg and 1.04 ± 0.04, respectively. ANG II caused sodium retention and a sustained increase in MAP of
30-35 mmHg. Throughout ANG II infusion, there was a greater rate
of sodium excretion from Inn vs. Den kidneys (day 5 Den/Inn sodium = 0.51 ± 0.05), indicating chronic suppression of
renal sympathetic nerve activity. CPD and CPD + SAD had little or
no influence on baseline values for either MAP or the Den/Inn sodium, nor did they alter the severity of ANG II hypertension. However, CPD
totally abolished the fall in the Den/Inn sodium in response to ANG II.
Furthermore, after CPD + SAD, there was a lower, rather than a
higher, rate of sodium excretion from Inn vs. Den kidneys during ANG II
infusion (day 5 Den/Inn sodium = 2.02 ± 0.14).
These data suggest that cardiac and/or arterial baroreflexes
chronically inhibit renal sympathetic nerve activity during ANG II
hypertension and that in the absence of these reflexes, ANG II has
sustained renal sympathoexcitatory effects.
renal nerves; arterial baroreflexes; cardiac reflexes; sympathetic nervous system; kidneys; sodium excretion
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