# Endogenous circannual rhythm in LH secretion: insight from signal analysis coupled with mathematical modelling

**Authors:** Alexandre Vidal, Claire Médigue, Benoit Malpaux, Frédérique Clément  
**arXiv:** [0903.1698](https://arxiv.org/abs/0903.1698)  
**Date:** 2009-03-10  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/0903.1698v1/

## Key points

- Sheep reproduction is timed by the annual photoperiodic cycle characterized by changes in daylength
- Photoperiodic information is translated into a circadian profile of melatonin secretion that impacts GnRH secretion, which controls ovarian cyclicity
- The pattern of GnRH secretion is mirrored into that of LH secretion, whose plasmatic level can be easily measured
- The authors investigate whether there exists an endogenous circannual rhythm in LH secretion in a tropical sheep population that exhibits clear seasonal ovarian activity when subjected to temperate latitudes
- The authors used time-frequency signal processing methods and designed a mathematical model of LH plasmatic level accounting for the effect of experimental sampling times to extract hidden rhythms from the data
- Their findings reveal the existence of an endogenous circannual rhythm and shed light on the action mechanism of photoperiod on the pulsatile pattern of LH secretion (control of interpulse interval)
- The high frequency component observed in their signals is mainly due to the experimental sampling protocol
- This study provides valuable insights into how photoperiod influences reproductive cycles in sheep
- Importance of considering experimental design when analyzing hormonal time series data

## Summary

The seasonal pattern of reproduction in sheep, as in many vertebrates, is timed by the annual photoperiodic cycle characterized by changes in daylength. This photoperiodic information is translated into a circadian profile of melatonin secretion that impacts gonadotrophin releasing hormone (GnRH) secretion, which controls ovarian cyclicity. The pattern of GnRH secretion is mirrored into that of luteinizing hormone (LH) secretion, whose plasmatic level can be easily measured. In this study, the authors investigate whether there exists an endogenous circannual rhythm in LH secretion in a tropical sheep population that exhibits clear seasonal ovarian activity when subjected to temperate latitudes. The authors based their analysis on LH time series collected over three years from ewes subjected to a constant photoperiodic regime. Due to intra- and inter-animal variability and unequal sampling times, the existence of an endogenous rhythm was not straightforward. To extract hidden rhythms from the data, they used time-frequency signal processing methods and designed a mathematical model of LH plasmatic level accounting for the effect of experimental sampling times. Their findings reveal the existence of an endogenous circannual rhythm and shed light on the action mechanism of photoperiod on the pulsatile pattern of LH secretion (control of interpulse interval). They also conclude that the high frequency component observed in their signals is mainly due to the experimental sampling protocol. This study provides valuable insights into how photoperiod influences reproductive cycles in sheep and highlights the importance of considering experimental design when analyzing hormonal time series data. The authors' approach combining signal processing techniques with mathematical modeling provides a powerful tool for investigating complex physiological systems such as those involved in reproductive cycles.