Regional differences in the regulation of contraction-relaxation machinery of vascular smooth muscle.

In the present study we revealed substantial differences in the regulation of the contraction-relaxation machinery of the middle cerebral and mesenteric arteries. a. Although K+-Krebs solution resulted in similar contractile responses in both vascular beds, norepinephrine, serotonin and PGF2 alpha were more potent in inducing contraction in the mesenteric artery than in the middle cerebral artery. Contrary, extremely high concentrations of acetylcholine produced negligible contractions in the mesenteric artery as compared to the middle cerebral artery. b. In more than 50% of the cases a considerable spontaneous tone developed in the middle cerebral artery, which was not due to the activation of adrenergic alpha receptors or some arachidonic acid metabolite. A similar phenomenon never occurred in the mesenteric artery. c. Acetylcholine, adenosine triphosphate and adenosine brought about similar dilatory concentration-response curves in the middle cerebral artery, but greatly different ones in the mesenteric artery where acetylcholine was the most, adenosine triphosphate the least potent dilator.