[Importance of ultradian rhythms in endocrinology]

Biological rhythms have been reported for a long time in endocrinology. However, their real study started in the late 60's when the possibility of repeatedly measuring the hormonal signal directly in blood over extended periods of time became available. Although episodic secretory fluctuations have been reported for the majority of hormones, and more specifically peptidic hormones, in mammals, organised secretory episodes on a regular or quasi-regular ultradian basis are less common. Their importance, which is directly connected to the number and the processing of the corresponding receptors on the target cells, is illustrated by the paradigm of the pulsatile release of the gonadotropin hormones. Hormonal ultradian rhythms should be considered both from the nosological and therapeutical point of view.