Diabetes Care, Vol 16, Issue 5 722-727, Copyright © 1993 by American Diabetes Association
Plasma norepinephrine in sensory diabetic polyneuropathy
C Tsigos, P Reed, C Weinkove, A White and RJ Young
Department of Medicine, University of Manchester, Hope Hospital, Salford, United Kingdom.
OBJECTIVE--To examine whether changes in circulating norepinephrine are
associated with the sensory disturbances of diabetic polyneuropathy.
Experimental studies have indicated that NE can excite sprouts from injured
nerves, producing pain. RESEARCH DESIGN AND METHODS--We measured supine and
erect plasma NE in 13 normal, nondiabetic control subjects and three groups
of diabetic patients: 20 without clinical neuropathy, 20 with chronic
painful neuropathy, and 15 with painless neuropathy and foot ulceration.
Neuropathy was characterized by symptom and deficit scores, sensory
thresholds, electrophysiology, and cardiovascular autonomic function tests.
Neuropathic pain was scored by the patients on a linear analogue scale.
RESULTS--In painless neuropathy, NE levels were greatly reduced (supine,
1.3 nM; erect, 2.2 nM) compared with control subjects (supine, 2.4 nM;
erect, 4.0 nM; P < 0.001) and were combined with grossly abnormal
autonomic reflexes. NE also was reduced in the diabetic group without
neuropathy (supine, 1.7 nM; erect, 2.7 nM; P < 0.01 vs. control
subjects). By contrast, in painful neuropathy NE levels (supine, 2.2 nM;
erect, 3.6 nM) were similar to control subjects and significantly higher
than in painless neuropathy (P < 0.01). Furthermore, NE correlated with
the severity of neuropathic pain (r = 0.46, P = 0.02). To assess whether
pain, acting as a stressor, could account for the observed differences in
NE, we also measured the stress hormones epinephrine and cortisol. They did
not differ among the diabetic groups. CONCLUSIONS--Circulating NE is higher
in painful than painless diabetic neuropathy. We suggest that painful
neuropathy is associated with a relatively higher number of functioning
sympathetic fibers that may contribute to pain.