AJP - Heart and Circulatory Physiology, Vol 247, Issue 6 952-H959, Copyright © 1984 by American Physiological Society
Tetrodotoxin-resistant relaxation to transmural nerve stimulation in isolated saphenous vein
M. Senaratne and T. Kappagoda
The response to transmural nerve stimulation (TNS) was characterized in
rings of canine saphenous veins following sympathetic (guanethidine 10(-4)
mol/l; phenoxybenzamine 2 X 10(-5) mol/l; propranolol 2 X 10(-6) mol/l) and
muscarinic blockade (atropine 5 X 10(-6) mol/l). In preparations which were
contracted with prostaglandin F2 alpha, TNS was applied as intermittent
trains of stimuli of 30 s duration at frequencies of 1-32 Hz. This stimulus
elicited a frequency-dependent relaxation [maximum relaxation 3.4 +/- 0.21
(SE) g]. This relaxation was present in rings denuded of endothelium and
was not altered significantly by cimetidine (10(-4) mol/l), indomethacin
(10(-5) mol/l), aminophylline (10(-5) mol/l), or cyproheptadine (10(-6)
mol/l). It was abolished by the Na+-K+-ATPase inhibitor ouabain (2 X 10(-4)
mol/l) and in zero-K+ Krebs solution. When the experiment was repeated
following storage of the isolated saphenous veins for 9 days at 4 degrees C
TNS failed to induce any relaxation. However, the relaxation in fresh rings
was not abolished by tetrodotoxin (10(-6) mol/l). The present study
demonstrates a nonadrenergic noncholinergic relaxation to TNS in the
saphenous vein which could be mediated by 1) a tetrodotoxin-resistant nerve
or 2) a direct effect of TNS on the smooth muscle.
