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 a ccumulation of tele-methylhistamine (t-MH), a major metabolite of brai n HA, following administration of pargyline. Intraperitoneal injection of 1, 2, and 4 U/kg of insulin, which had no influence on steady-stat e levels of HA and t-MH, increased pargyline-induced accumulation of t -MH. Accumulation of t-MH due to pargyline was inversely related to th e concomitant plasma glucose concentration after different doses of in sulin. The level of t-MH accumulated by pargyline did not change compa red 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 cerebr oventricle. Intracerebroventricular infusion of 24 mu mol per rat of 2 -DG, which had no influence on steady-state levels of HA and t-MH, inc reased the level of t-MH enhanced by pargyline. The results indicate t hat an increase in hypothalamic HA turnover in response to glucoprivat ion may be involved in homeostatic regulation of energy metabolism in the brain.