Vasopressin (VP) production in the Suprachiasmatic Nucleus (SCN) is influenced by the rhythm of clock genes and the light-dark cycle. The circadian production and release of VP from SCN terminals is one of the core signals via which the biological clock imposes its rhythm on its target structures. It is a critical element in the circadian regulation of corticosterone secretion, reproductive cycle, and metabolism in rodents. All these circadian variables are regulated within very narrow boundaries at a specific time of the day, indicating the need for an elaborate feedback system to inform the SCN about the actual levels reached during the circadian cycle. Here, we emphasize its role in glucose and Corticosterone secretion with the question of how the SCN is informed about their actual levels in circulation.Both corticosterone and glucose have their daily nadir at the beginning of the sleep phase, induced by increased SCN-VP neuron activity. Both corticosterone and glucose levels in the general circulation are sensed in the arcuate nucleus (ARC), which is vital for their circadian regulation. To explore this feedback mechanism, we injected a small dose of corticosterone or glucose into the general circulation at the beginning of the sleep phase in free-moving animals. In line with the observation that increased SCN-VP neuronal activity reduces corticosterone and glucose levels, the injection of corticosterone increases the activity of SCN-VP neurons. However, in contrast with corticosterone, glucose injection lowers VP neuron activity in the SCN. This seemingly contradictory result will be discussed during the presentation.