THE CEREBRAL CIRCULATION

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Abstract
From 21 experiments on 10 cats under amytal, 11 experiments on 5 cats under ether, and 2 experiments on cats under both amytal and ether, the authors conclude that vessels of the brain react to intravenous injection of histamine in a very different manner, depending on whether the animal is under ether or amytal anesthesia. Under amytal the vessels of the brain dilate (following intravenous injection of histamine) and the cerebrospinal fluid pressure rises. The same results follow small doses of histamine in non-anesthetized man. Under ether the vessels of the brain are already dilated, and little if any further dilatation follows the intravenous injection of histamine; instead they often become narrower and cerebrospinal fluid pressure falls. Local application of histamine to the surface of the brain always results in dilatation of the pial vessels, without noticeably affecting intracranial or systemic vascular pressures. Intravenous injection of histamine (in animals under amytal) causes great pial artery dilatation in spite of a coincident fall in systemic arterial pressure. Chemical changes in the blood are often more powerful than alterations in blood pressure as a means of regulating the caliber of the pial blood vessels in mammals.

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