[The effect of ganglionectomy and cold exposure on the ventromedial hypothalamic nucleus, blood glucose and liver glycogen in regard to circadian rhythms].

To analyse the importance of the ventromedial hypothalamic nucleus (VMH) for the circadian regulation of the carbohydrate metabolism rats were investigated after bilateral cervical sympathetic ganglionectomy (SCGx) 30 d earlier and exposure to cold (10 degrees C) 72 h earlier. In order to assess the circadian rhythms of nuclear volume oscillations of the VMH, blood glucose, and liver glycogen 4 times a day (light-dark cycle: 14L:10D, light on 05.00 h) rats were sacrificed at midlight and middark as well as 1 h after the onset of the light and dark periods. The circadian curves were calculated in a model-free way by the procedures of locally adjusted polynomial approximation. Ganglion removal and exposure to cold resulted in an increase of blood sugar and of nuclear volume of the VMH, but only of its lateral part. The liver glycogen decreased. Additionally, both the coordination between the circadian curves of the nuclear volume and of the blood glucose as well as of the inverse curves of the liver glycogen was destroyed after SCGx. These results are in agreement with the conviction that the enhanced blood glucose activates the VMH. The augmentation of blood glucose was discussed in connection with influences of the likewise increased thyrotropin-releasing hormone and thyrotropin on the increased plasma levels of catecholamines, with secondary increased plasma levels of glucagon as well as decreased insulin levels after SCGx and exposure to cold. The sympathetic denervation of the pineal gland (SCGx) produced the mentioned desynchronization of the curves. At the present we are not able to explain the approximate restitution of the circadian rhythms after additional exposure to cold.