Long-lasting cardiovascular
depression induced by acupuncture-like stimulation of the sciatic nerve
in unanaesthetized spontaneously hypertensive
rats.
Yao T, Andersson S, Thoren P.
The
influence of a prolonged low frequency electrical stimulation of the
somatic afferents on cardiovascular and sympathetic nerve activities was
investigated in unanaesthetized spontaneously hypertensive rats (SHRs)
and Wistar-Kyoto normotensive rats (WKRs). In SHR, an elevation of blood
pressure, heart rate and splanchnic nerve outflow was elicited during a
30-min period of sciatic nerve stimulation. Following the cessation of
the stimulation, depressor response and bradycardia slowly developed and
lasted up to 12 h. Activation of the group III or A-delta afferent
fibers was essential for this post-stimulatory response. The progressive
depressor response and a parallelled reduction of the splanchnic nerve
activity, reached their maxima at about 1 h after the termination of the
sciatic stimulation. The magnitude of the post-stimulatory depressor
response was correlated with the prestimulatory control blood pressure
level. There were also behavioural changes accompanying the depressor
response. The cardiovascular and the behavioural depression were
immediately reversed by naloxone (10-15 mg/kg, i.v.). The
post-stimulatory depressor response was still present after bilateral
sino-aortic denervation, but was absent in animals anaesthetized with
chloralose and urethane. Emotional stress produced by air-blowing on the
animal resulted in pressor response and tachycardia during the period of
the stressful stimulation, but there was no depressor response following
the termination of air-blowing. These findings indicate a sympathetic
and cardiovascular depression induced by a prolonged stimulation of the
somatic group III or A-delta afferent fibers; its long duration and
naloxone reversibility suggest the involvement of endorphins in the
mechanism of this response. The physiological significance of the
effects of the prolonged somatic afferent stimulation and its possible
relations with acupuncture are discussed.