We investigated the effects of diabetes mellitus and antioxidant treatment
on the sensory and reflex function of cardiac chemosensory nerves in rats.
Diabetes was induced by streptozotocin (STZ; 85 mg/kg ip). Subgroups of sha
m- and STZ-treated rats were chronically treated with an antioxidant, vitam
in E (60 mg/kg per os daily, started 2 days before STZ). Animals were studi
ed 6-8 wk after STZ injection. We measured renal sympathetic nerve activity
(RSNA), mean arterial blood pressure (MABP), and cardiac vagal and sympath
etic afferent activities in response to stimulation of chemosensitive senso
ry nerves in the heart by epicardial application of capsaicin (Caps) and br
adykinin (BK). In cardiac sympathetic-denervated rats, Caps and BK (1-10.0
mug) evoked a vagal afferent mediated reflex depression of RSNA and MABP, w
hich was significantly blunted in STZ-treated rats (P < 0.05). In vagal-den
ervated rats, Caps and BK (1-10.0 <mu>g) evoked a sympathetic afferent-medi
ated reflex elevation of RSNA and MABP, which also was significantly blunte
d in STZ-treated rats (P, 0.05). Chronic vitamin E treatment effectively pr
evented these cardiac chemoreflex defects in STZ-treated rats without alter
ing resting blood glucose or hemodynamics. STZ-treated rats with insulin re
placement did not exhibit impaired cardiac chemoreflexes. In afferent studi
es, Caps and BK (0.1 g-10.0 mug) increased cardiac vagal and sympathetic af
ferent nerve activity in a dose-dependent manner in sham- treated rats. The
se responses were significantly blunted in STZ-treated rats. Vitamin E prev
ented the impairment of afferent discharge to chemical stimulation in STZ r
ats. The following were concluded: STZ-induced, insulin-dependent diabetes
in rats extensively impairs the sensory and reflex properties of cardiac ch
emosensitive nerve endings, and these disturbances can be prevented by chro
nic treatment with vitamin E. These results suggest that oxidative stress p
lays an important role in the neuropathy of this autonomic reflex in diabet
es.