Effect of fasting on myocardial glucose uptake in rabbits

In the present study, the effect of fasting on myocardial glucose uptake was studied. Two different techniques were used, namely cardiac muscle slices [0.5 mm thick] and the isolated heart perfusion using Langendorff's coronary technique. The effect of fasting for 1, 2, 3 and 4 days on glucose uptake was studied in both groups of experiments and the results were compared with control fed animals. The present results showed that in both groups of experiments [slices and isolated heart perfusion], fasting caused a significant increase in glucose uptake, an effect which was potentiated by increasing the duration of fasting. These results differed from previous studies which reported decreased glucose uptake by starvation. This difference could be explained by the difference in the substrate used, since previous studies used glucose and free fatty acids in the used solution or injected radioactive glucose in vivo then measured radioactivity after killing the animals, while in the present study glucose only was used as a substrate. The increase in glucose uptake could, also, be explained by its use for glycogen synthesis in cardiac muscle

Age-related differences in metabolic responses to acute immobilizatin stress

The purpose of this study was to determine whether responses of acutely stressed rats would vary as a function of age between animals having no previous experience of immobilization [stress naive] and those trained to immobilization [IMO] for 3 days [stress trained]. Adult young [4 months old] and aged [22 months old] male albino rats were used. The results presented no evidence of age related difference in resting plasma glucose [PGL], insulin [INS] or free fatty acids [FFA]. IMO stress, however, resulted in hyperglycemia, hypoinsulinemia and increased FFA levels in both young and aged rats. Stress induced hyperglycemia reached a higher level and decreased at a slower rate in old compared with young rats. Stress-trained young rats showed significantly higher PGL compared to stress na‹ve rats at 15 min. and 1 of IMO, whereas no such difference was observed in aged rats. PGL was significantly higher in young trained rats at 15 min. of IMO compared to old trained rats. Regarding the hypoinsulinemia observed, young rats showed a greater stress-induced insulin suppression than old rats. Stress-trained young rats showed a significantly lower insulin levels as compared to corresponding age matched stress naive rats at 15 min. of IMO, but no such difference was observed in old rats. Moreover, young trained rats showed significantly lower INS levels compared to corresponding old rats. The rise of FFA was more pronounced in old than young rats at 15 min. of IMO, while no difference was observed between the two age groups at 1 hour of IMO. On the other hand, trained young rats showed significantly higher FFA levels as compared to age matched stress na‹ve group at both periods of IMO, while in old trained rats there was a significant decrease in FFA at 15 min. and no difference at 1 hour of IO compared to stress na‹ve age matched rats. Young trained rats showed significantly higher FFA levels compared to old trained rats. These findings support the following conclusions: 1] there is no age-related difference in resting PGL, INS and FFA levels. 2] Acute IMO stress results in hyperglycemia, hypoinsulinemia and rise in FFA levels. 3] These stress-induced metabolic responses differ according to age training of the animal. 4] Young but not aged rats show a rapid modulation of adaptive metabolic responses to short term receptivity IMO