Elevation of plasma triglyceride levels due to 2-deoxy-D-glucose in conscious rats

Gold-thioglucose-induced hypothalamic lesions inhibit metabolic modulation of light-induced circadian phase shifts in mice

The circadian clock located in the suprachiasmatic nuclei is entrained by the 24-h variation in light intensity. The clock's responses to light can, however, be reduced when glucose availability is decreased. We tested the hypothesis that the ventromedial hypothalamus, a key area in the integration of metabolic and hormonal signals, mediates the metabolic modulation of circadian responses to light by injecting C57BL/6J mice with gold-thioglucose (0.6 g/kg) which damages glucose-receptive neurons, primarily located in the ventromedial hypothalamus. Light pulses applied during the mid-subjective night induce phase delays in the circadian rhythm of locomotor activity in mice kept in constant darkness. As previously observed, light-induced phase delays were significantly attenuated in fed mice pre-treated with 500 mg/kg i.p. 2-deoxy-D-glucose and in hypoglycemic mice fasted for 30 h, pre-treated with 5 IU/kg s.c. insulin or saline, compared to control mice fed ad libitum. In contrast, similar metabolic challenges in mice with gold-thioglucose-induced hypothalamic lesions did not significantly affect light-induced phase delays compared to mice treated with gold-thioglucose and fed ad libitum. These results indicate that destruction of gold-thioglucose-sensitive neurons in the ventromedial hypothalamus prevent metabolic regulation of circadian responses to light during shortage of glucose availability. Therefore, the ventromedial hypothalamus may be a central site coordinating the metabolic modulation of light-induced phase shifts of the circadian clock.

Dual 24-hour feeding response to 2DG in rats: daytime increase and nighttime decrease

Thirty-six rats were injected IP with 2DG (0, 250, or 500 mg/kg) at 7-day intervals, once at light onset (7 a.m.) and once at dark onset (7 p.m.), and postinjection food intake was monitored for 24 hours. Five hundred mg/kg 2DG caused food intake to rise above control levels during the first 6 hours of daylight, regardless of whether the injection had occurred that morning or the previous evening, whereas intake during the first 6 hours of darkness was consistently below control levels. In a second study, 24 rats were injected first at 7 a.m. (500 mg/kg 2DG or saline), and 7 days later at 7 p.m. (opposite drug), and food was withheld 12 hours until the light:dark period had changed. For 12 hours after food was returned, 2DG again decreased nighttime food intake (Injection 1) and increased daytime intake (Injection 2). 2DG's dual long-term effects cannot be accounted for either by malaise or by an initial action that later is compensated by its opposite. Rather, 2DG (500 mg/kg) appears to exert two independent, opposite alimentary effects which persist 18-24 hours and which change direction with phase changes in the light:dark cycle.

Effects of chronic administration of benfluorex to rats on the metabolism of corticosterone, glucose, triacylglycerols, glycerol and fatty acid

(1) Rats were fed on diets enriched with sucrose, beef tallow or corn oil and treated for 11-16 days with 50 mg of benfluorex per kg of body weight. By these times the growth rate and food intake were not significantly different from those of control rats. (2) Benfluorex approximately halved the concentration of circulating triacylglycerol in rats fed the beef tallow or sucrose diets. (3) It did not significantly alter the total lipoprotein lipase activity in diaphragm, heart and adipose tissue. (4) The clearance of triacylglycerols from chylomicrons exhibited two t 1/2 values of about 0.6 and 6.9 min in rats fed the beef tallow diet. Benfluorex did not significantly alter these values. (5) Benfluorex did not significantly alter the rate of appearance of triacylglycerol in the blood of rats injected with Triton WR 1339 to block triacylglycerol uptake. It did, however, decrease the rise in circulating glucose which presumably resulted from the stress of the procedure. (6) Benfluorex decreased the extent and duration of the rise in serum corticosterone when rats maintained on the corn oil diet were fed acutely with fructose. It also decreased the circulating concentrations of glycerol, triacylglycerol and glucose after fructose feeding. (7) Rats fed on the corn oil diet and then treated with benfluorex had lower concentrations of circulating glucose, triacylglycerol, glycerol and fatty acids after being injected with 2-deoxyglucose. (8) It is proposed that some of the long-term hypoglycaemic and hypotriglyceridaemic effects of benfluorex could be mediated indirectly through changes in endocrine balance, perhaps via the serotonergic system and in particular, by decreasing the effects of stress hormones relative to insulin. The implications of these findings are discussed in relation to controlling metabolism in stress conditions and for the management of obesity, diabetes and atherosclerosis.

Increased adenine nucleotides in liver mitochondria after mannoheptulose injection in vivo

In adult rats, mannoheptulose injection causes a transient decrease in the serum insulin-to-glucagon ratio and a concomitant increase in serum glucose concentration. These effects attain a maximum 1 h after the injection and then decline toward normal. Correlated with the hormone changes is a dramatic increase in the adenine nucleotide content (ATP + ADP + AMP) of liver mitochondria, which peaks to over 50% of control values at 1 h. The increase in mitochondrial adenine nucleotides must occur by uptake from the cytosol, because the adenine nucleotide content of the whole tissue remains constant. The accumulation of adenine nucleotides by the mitochondria probably occurs over the recently characterized carboxyatractyloside-insensitive transport pathway that allows exchange of ATP-Mg for Pi. The actual mechanism by which net uptake is regulated after mannoheptulose injection has not yet been elucidated; however, changes in the Km or Vmax of the carrier and an increase in the tissue ATP/ADP ratio were eliminated as possibilities. The increase in matrix adenine nucleotide content in response to hormone changes brought about by mannoheptulose was much greater and more reproducible than what is achieved with glucagon injection. Mannoheptulose treatment may therefore be preferable as a model for further study of hormone effects on mitochondrial function.