The Dilator Effect of Histamine on the Cerebral Vessels in Man.

Abstract

Direct evidence as to whether or not the cerebral vessels in man possess vasomotor play is still lacking.

The following observations on patients indicate that the arterioles, capillaries, and venules of the human brain respond with prompt dilatation to histamine.

Following the intravenous administration of an average dose of 0.07 mg. (0.7 cc. of a solution of 1:10,000) of histamine phosphate the spinal fluid pressure showed a marked rise. The onset of this rise occurred about simultaneously with the circulation time of the injected histamine. During and slightly after the rise of the spinal fluid pressure the excursions of the oscillatory pulsation of the spinal fluid were greatly increased, although there was no demonstrable rise in the simultaneously registered arterial or venous blood pressure. Coincident with these objective changes there was a sensation of throbbing and pressure in the head.

A small amount of histamine phosphate administered intravenously, when the hemisphere was exposed for the purpose of removal of tumor, caused a prompt bulging of the brain, a distinctly increased cerebral pulsation, and a visible bright flush of the brain surface. These changes, just as other bodily responses following the single intravenous dose, lasted but 0.5 to 3 minutes. Forbes, Wolf and Cobb have observed a similar behaviour of the small pial vessels of the cat.

Adult subjects tolerated well the continuous intravenous administration of 0.05 to 0.1 mg. of histamine phosphate per minute of a solution of 1:10,000. The oxygen and carbon dioxide content of the arterial blood flowing to, and the venous blood returning from the brain was measured. It was observed that while the arterial blood during the administration of histamine showed an average increase of 8% in the oxygen content, because of increased concentration of the blood; the oxygen content of the blood obtained from the internal jugular vein showed an average rise of 20% over the value found before the injection of histamine. During identical experimental conditions the average increase in the oxygen content of the blood obtained from the external jugular vein was 12%, and that from the basilic vein 24%. The average decrease of the carbon dioxide content of the blood obtained from the internal jugular vein was 9%.