Effect of microinjection of histamine into the brain on plasma levels of epinephrine and glucose in freely moving rats

The effect of histamine administered to the brain on the plasma levels of epinephrine, norepinephrine and glucose was investigated in freely moving rats. Histamine (10 micrograms) administered intracerebroventricularly (into the lateral ventricle) induced a hyperglycemic response with preceding increases in plasma catecholamines, especially epinephrine. When histamine (5 micrograms) was injected into three different levels of the ventricular system, the magnitude and duration of the resulting increases in plasma epinephrine and glucose were in the following rank order: the third ventricle greater than aqueduct much greater than fourth ventricle. These results suggest that the sites of action of histamine are located rostrally from the midbrain. Microinjections of histamine (1 microgram) into the hypothalamic nuclei including the medial preoptic area, paraventricular nucleus, ventromedial hypothalamic nucleus, posterior hypothalamic nucleus and mammillary body had no elevating effect on the plasma levels of epinephrine and glucose. Other brain regions, such as the lateral septum, medial amygdaloid nucleus and periaqueductal grey of the midbrain, were also excluded as possible sites of histamine action. From the present results, it seems that histamine stimulates plural sites close to the ventricular system to induce hyperglycemic responses.