[Lipogenesis, lipolysis and feeding rhythms]

Recordings of rat's diurnal ad libitum feeding patterns and responses to short term food deprivation suggested that analysis of diurnal feeding rhythms could provide a clue for understanding mechanisms involved in control and regulation of food intake. A simultaneous recording of free feeding patterns and of respiratory exchanges showed that a nocturnal positive energy balance and hyperphagia were mainly due to a diversion of ingested nutrients to fat deposition while negative energy balance and hypophagia during daytime were an effect of fat mobilization and oxidation. Further it was demonstrated that a neuroendocrine diurnal cycle underlined the lipogenesis-lipolysis cycle with hyper-insulinism and glucose tolerance at night, hypoinsulinism and glucose intolerance during the day. Similar phenomena were found along with the human scheduled feeding. Negative correlations between nocturnal lipogenesis and subsequent daytime lipolysis and the diurnal cycle of free fed rats compared to experimentally induced and reversible obesity and to seasonal cycles of hibernators give evidence on the nature of the lipostatic mechanism and its monitoring by hypothalamic ventromedial nuclei.