Neuronal Glucoprivation Enhances Hypothalamic Histamine Turnover in Rats

: Histamine (HA) turnover in the rat hypothalamus following insufficient energy supply due to glucoprivation was examined after administration of insulin or 2‐deoxy‐d‐glucose (2‐DG). HA turnover was assessed by accumulation of tele‐methylhistamine (t‐MH), a major metabolite of brain HA, following administration of pargyline. Intraperitoneal injection of 1, 2, and 4 U/kg of insulin, which had no influence on steady‐state levels of HA and t‐MH, increased pargyline‐induced accumulation of t‐MH. Accumulation of t‐MH due to pargyline was inversely related to the concomitant plasma glucose concentration after different doses of insulin. The level of t‐MH accumulated by pargyline did not change compared with that of controls, when a euglycemic condition was maintained or insulin at a dose of 6 mU per rat was infused into the third cerebroventricle. Intracerebroventricular infusion of 24 µmol per rat of 2‐DG, which had no influence on steady‐state levels of HA and t‐MH, increased the level of t‐MH enhanced by pargyline. The results indicate that an increase in hypothalamic HA turnover in response to glucoprivation may be involved in homeostatic regulation of energy metabolism in the brain.