Sympathetic vasoconstrictive responses to high and low sodium diets
in diabetic and normal subjects.
Miller, Judith A., With The Expert Technical Assistance Of Julie C.
Dionne.
Department of Medicine, University of Toronto, Canada
APStracts 2:0042R, 1995.
Uncomplicated insulin dependent diabetes mellitus (IDDM) has been
associated with both a suppression of the reflex response to stimuli
which activate the sympathetic nervous system (SNS) and an enhanced
pressor response to catecholamines. The aim of these experiments was
to examine cardiovascular regulation by the SNS in subjects with
uncomplicated IDDM within 5 years of diagnosis to determine the
responsible mechanism within the cardiopulmonary baroreflex arc, and
the potential role played by extracellular fluid volume (ECFV)
expansion. The integrity of the reflex arc was tested by examining
the plasma norepinephrine (PNE) and forearm vascular (FVR) responses
to cardiopulmonary baroreceptor deactivation by non-hypotensive Lower
Body Negative Pressure (LBNP). The integrity of the effector limb was
tested by measuring the PNE, FVR and mean arterial pressure (MAP)
response to the Cold Pressor Test (CPT), a non-baroreceptor-mediated
stimulus. The postganglionic neuroeffector junction was tested by
measuring the venoconstrictive response to local norepinephrine
infusion. ECFV was varied by altering the content of sodium in the
diet. In subjects with IDDM, PNE and FVR responses to cardiopulmonary
baroreceptor deactivation were attenuated, the MAP, FVR, and PNE
responses to the CPT were intact, and the peripheral vasculature was
hyper-responsive to norepinephrine infusion compared to control
subjects. Sodium restriction resulting in ECFV contraction and
reductions in central venous pressure normalized the FVR response to
LBNP and the venous response to norepinephrine infusion in subjects
with IDDM, without affecting the response in control subjects. In
subjects with IDDM, the PNE response both to LBNP and the CPT
remained attenuated with sodium restriction, even though other
measures of sympathetic function were normalized. These data indicate
that 1) sympathoinhibition in subjects with early IDDM may be a
normal reflex response to increased cardiac filling pressures,
mediated by cardiopulmonary baroreceptors; 2) sodium restriction
normalizes both the cardiopulmonary baroreflex control of FVR and the
hyper-reactivity of the peripheral vasculature to norepinephrine
infusion; and 3) the measurement of PNE alone is inadequate to assess
SNS activity in diabetic patients.
Received 10 September 1994; accepted in final form 27 January
1995.
APS Manuscript Number R505-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.