Electrical field stimulation-mediated relaxation of rabbit middle cerebral artery. Evidence of a cholinergic endothelium-dependent component.
The effects of electrical field stimulation (EFS) of rabbit middle cerebral arteries were examined using wire-mounted arterial segments. EFS of segments maintained at rest tension caused a tetrodotoxin-sensitive sympathetic contraction. In agonist-contracted segments maintained at approximately 60% of tissue maximum force, EFS caused a relaxation in two thirds of the preparations. Maximum response (mean +/- SEM) was 33 +/- 3.5% of maximal relaxation. The EFS relaxation was tetrodotoxin-sensitive but was not blocked by either chronic surgical sympathectomy or exposure to guanethidine (5 microM). Electron microscopy of chromaffin-fixed arterial sections showed the presence of chromaffin-positive large and small vesicles. Within the same sheath of Schwann were also a smaller number of nerve profiles containing many small clear vesicles. Removal of the vascular endothelium or treatment with atropine (10 nM) eliminated the EFS relaxation in approximately 50% of the segments and reduced the response in another 35-40%; in the remainder, relaxation was unaffected. Combined data for endothelium removal and atropine treatment showed that each caused a significant (p less than 0.01) reduction in the EFS relaxation. Atropine also significantly reduced EFS relaxation in guanethidine-treated segments. There was no reduction in EFS relaxation after procedures that antagonized ATP- or substance P-mediated relaxations. These results indicate that EFS of precontracted rabbit middle cerebral artery causes a neurogenic nonadrenergic relaxation. The neuroeffector mechanism mediating this response has a predominantly cholinergic endothelium-dependent component as well as a noncholinergic endothelium-independent component.
Van Riper
D A
DA
University of Vermont, Department of Pharmacology 05405.
Bevan
J A
JA
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002536:Cerebral Arteries / Q000294:innervation* / Q000502:physiology; D002799:Cholinergic Fibers / Q000502:physiology*; D004558:Electric Stimulation; D004730:Endothelium, Vascular / Q000294:innervation*; D006145:Guanethidine / Q000494:pharmacology; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D009126:Muscle Relaxation; D009131:Muscle, Smooth, Vascular / Q000294:innervation* / Q000502:physiology; D018377:Neurotransmitter Agents / Q000502:physiology*; D011817:Rabbits; D013562:Sympathectomy
D018377:Neurotransmitter Agents; D001285:Atropine; D006145:Guanethidine