| Abstract: | The effects of bilateral lesions of the ventromedial hypothalamus (VMH) on daily rhythms of the activity of a gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), in the liver and kidney of rats were examined. PEPCK activity in the liver was considerably lowered by VMH lesions, but its rhythm remained similar to that of control liver. In contrast, PEPCK activity in the kidney was markedly elevated by the lesions. From these findings, it is suggested that the VMH is not the site of the master biological clock of the rhythm of PEPCK activity. Although these results do not exclude the possibility that hyperphagia and hyperinsulinemia associated with VMH lesions induce changes in the levels of PEPCK activities, they support the hypothesis that suppression of the sympathetic nervous system causes the changes in PEPCK activity through direct or indirect mechanisms. These findings also suggest that the reciprocal change in PEPCK activities in the liver and kidney after VMH lesions is related to complementary functions of the two organs in maintenance of homeostasis of blood glucose. |
