Threshold levels of 2-deoxy-D-glucose for the hyperglycemic response: dog and goat compared

Relevance of hyperglycemia to dieldrin toxicity in suckling and adult rats

Acute exposure to dieldrin (HEOD) causes hyperglycemia and death in the adult rat. Whether the hyperglycemia contributes to the mortality was studied in 10- and 60-day-old Wistar rats given an LD50 dose of the insecticide (pups, 28 mg/kg p.o. and adults, 63 mg/kg p.o.). HEOD elevated blood glucose 2-fold in the adult but had no effect in the pup. d-Glucose (6 g/kg p.o., 0, 3, 6 and 18 h post HEOD) reduced by 79% the 24-h mortality the insecticide caused in the 10-day-old rat. Thus, hyperglycemia in the immature rat protects against dieldrin toxicity. Conversely, the 24-h mortality was not significantly affected in adult rats whose HEOD-induced hyperglycemia was increased with either d-glucose (6 g/kg p.o., every 2 h post HEOD) or 2-deoxyglucose (1 g/kg s.c., concomitant with the HEOD). Phenobarbital (40 mg/kg i.p., concomitant with the insecticide) significantly decreased both the hyperglycemia (23%) and the 24-h mortality (86%) in HEOD-treated adult rats. The administration of d-glucose (6 g/kg p.o., 0, 3, 9 and 18 h post HEOD) to phenobarbital and HEOD-treated animals restored the hyperglycemia and returned the 24-h mortality to that found in animals given dieldrin alone. Thus, in the adult rat HEOD-induced hyperglycemia is a component of dieldrin toxicity.

Alloxan-induced glucoprivic feeding deficits are blocked by D-glucose and amygdalin

Intracerebroventricular injection of alloxan, a pancreatic beta (B) cell cytotoxin, impairs glucoprivic feeding in rats. The goal of this experiment was to determine whether alloxan-induced impairment of glucoprivic feeding can be attenuated by agents which antagonize alloxan's toxicity in the B cell. Therefore, alloxan was co-administered into the fourth ventricle alone or in combination with D-glucose, L-glutamine, or amygdalin, all known antagonists of alloxan's B cell toxicity, or with L-glucose, which does not antagonize B cell toxicity. We found that alloxan produced deficits in glucoprivic feeding which were not attenuated by co-administration with L-glucose or L-glutamine. Alloxan/L-glucose treated rats ate 11% and 14% of control intake, respectively, after systemic administration of 2-deoxy-D-glucose (2DG, 250 mg/kg) and fourth ventricular 5-thioglucose (5TG, 120 micrograms/5 microliter). Alloxan/L-glutamine rats ate 20% and 22% of control intake after 2DG and 5TG, respectively. In contrast, D-glucose and amygdalin (15 mM) completely blocked alloxan-induced impairment of glucoprivic feeding and amygdalin (10 mM) exerted a partial protective effect. These behavioral results may indicate that in the brain, susceptibility to alloxan toxicity depends upon cellular characteristics shared with the B cell.

Insulin-induced elevation of hypothalamic norepinephrine turnover persists after glucorestoration unless feeding occurs

We employed a delayed feeding paradigm to assess regional brain catecholamine changes associated with insulin-elicited glucoprivic feeding. This paradigm makes use of the recent discovery that glucoprivic challenges significantly enhance food intake even when food is withheld until other signs of glucoprivation have abated. Using this paradigm we attempted to temporally dissociate the neurochemical events associated with the ingestive response from other potentially confounding consequences of insulin or glucoprivation. We found a high degree of congruence between elevated hypothalamic norepinephrine (NE) turnover (estimated by the change in transmitter concentration after synthesis inhibition) and the persistence of hunger, both during and after apparent glucoprivation. In the absence of food, hypothalamic NE turnover was enhanced during insulin-induced glucoprivation and this increase persisted into the postglucoprivic period. A brief feeding bout, either during glucoprivation or postglucoprivically, rapidly normalized NE turnover rates. Moreover, brief access (30 min) to a limited quantity of food (2.5 g) during glucoprivation abolished both the elevated turnover and the feeding response otherwise observed postglucoprivically. Turnover of catecholamines in the telencephalon was also enhanced after insulin, but the increased activity did not persist into the postglucoprivic period and, in addition, was not altered in any consistent manner by food intake. These findings strengthen the view that hypothalamic NE neurons are involved in the mediation of glucoprivic feeding.

Differential effects of 2-deoxy-D-glucose on plasma glucose, free fatty acids and feeding during the light and dark cycle in rats

The effects of 2-deoxy-D-glucose (2-DG) combined with 0 to 6 hr of food deprivation on plasma glucose (PG), plasma free fatty acid (PFFA) levels and feeding were compared during the 2 parts of the diurnal cycle. In one group, PG and PFFA were measured prior to the injection of either 2-DG or saline and 90 min after injections without restoration of access to food. In a second group, food was reintroduced following injection and intake was measured. At night, PG and PFFA measured prior to injections decreased and increased with respect to the length of food deprivation. Ninety minutes after 2-DG, PG and PFFA were elevated above control levels as a function of previous deprivation. During the day, fasting time did not affect PG and PFFA 90 min after a saline injection; but, after 2-DG, PG increased and PFFA decreased irrespective of the previous deprivation period. At night, food intake increased after saline and 2-DG as a function of fast duration, but increases were significantly lower after 2-DG. During the day, the duration of food deprivation did not affect food intake after 2-DG and saline; but irrespective of previous food deprivation, the cumulative intake of the first 2 hr was higher after 2-DG. Results are discussed in relation to the dual activation by 2-DG of facilitatory and inhibitory mechanisms of food intake.