Ultradian rhythm

In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day.

The Oxford English Dictionary's definition of Ultradian specifies that it refers to cycles with a period shorter than a day but longer than an hour.

Other ultradian rhythms include blood circulation, blinking, pulse, hormonal secretions such as growth hormone,[3] heart rate, thermoregulation, micturition, bowel activity, nostril dilation, appetite, and arousal.

[4] Recently, ultradian rhythms of arousal lasting approximately 4 hours were attributed to the dopaminergic system in mammals.

[5] When the dopaminergic system is perturbed either by use of drugs or by genetic disruption, these 4-hour rhythms can lengthen significantly into the infradian (> 24 h) range, sometimes even lasting for days (> 110 h) when methamphetamine are provided.

Leptin circadian cycle, interfered by three meals. One can see that leptin goes high during the day, then it falls off, before starting the cycle again. The line is a fitted curve to the experimental data, using polynomial expansion , in order to show the periodic behavior of the data.