Adrenergic vasoconstriction of the goat middle cerebral artery

The effects of field electrical stimulation on the contractile response of the isolated middle cerebral artery of the goat were evaluated before and after the use of experimental procedures designed to test the adrenergic component involved. Supramaximal stimuli produced frequency-dependent increases in tension. This response was significantly reduced by phentolamine (10(-6) M), tetrodotoxin (3 X 10(-6) M), and bretylium (5 X 10(-5) M), but not by cocaine (10(-6) M). Arterial segments from goats pretreated with reserpine and from goats in which both superior cervical sympathetic ganglia had been removed 12 days prior to the experiment also showed a significant decrease in the contraction elicited by electrical stimulation. The norepinephrine concentration of the arteries of the circle of Willis from control goats was 2.10 microgram per gram of tissue. Reserpine or gangliectomy reduced the catecholamine content to undetectable levels. It is likely that a major part of the contractile response of cerebral arteries to electrical stimulation is due to release of endogenous norepinephrine which in turn activates the alpha-adrenergic receptors.