SUPPRESSION OF LUTEINIZING-HORMONE PULSES BY RESTRICTION OF GLUCOSE AVAILABILITY IS MEDIATED BY SENSORS IN THE BRAIN-STEM

The availability of metabolic fuels such as glucose is known to influe nce reproductive function. Peripheral administration of 2-deoxyglucose (2DG), a competitive inhibitor of glycolysis, inhibits pulsatile LH s ecretion in the rat and growth-retarded lamb. We hypothesized that suc h glucoprivic suppression of LH secretion is mediated by the lower bra in stem, because studies of both ingestive and reproductive behavior i mplicate lower brain stem structures, such as the area postrema, as a site that is sensitive to glucose availability. In the present study, the effect of a 2DG infusion, targeted to the fourth ventricle, on pul satile LH secretion was examined in male rats. The males were castrate d or castrated and immediately implanted with testosterone. Blood samp les were collected through an indwelling atrial cannula every 6 min fo r 4 h for LH determination. After the first hour of blood sampling, 2D G (4 or 40 mg/kg) was infused into the fourth ventricle at a now rate of 0.2 mu l/min through a cannula that had been stereotaxically implan ted 1 week before sampling. The high dose of 2DG (40 mg/kg), but not t he low dose (4 mg/kg), suppressed pulsatile LH secretion and increased food intake in both castrated and testosterone-treated castrated rats . LH secretion and food intake were not affected by the infusion of xy lose (40 mg/kg) as an isoosmotic control. The site specificity of the 2DG treatment was confirmed by histological examination after an isovo lumetric infusion of dye (0.2 mu l/min). These results suggest that gl ucose availability could influence LH secretion as well as feeding thr ough a central sensor in the lower brain stem and are consistent with the idea that the area postrema might be an important glucosensor invo lved in the modulation of LH secretion.