Abstract

Simple SummaryDuring the course of evolution, animals have evolved biological rhythms that are associated with changes in the lighting and temperature of their environment. Females in most breeds of sheep are seasonal breeders, with ovulatory cycles occurring in the autumn and winter and anovulation in the spring and summer. Secretion of gonadotropin releasing hormone and luteinizing hormone, the main hormones regulating reproduction in females, displays a circadian pattern; however, data concerning the day/night differences in their secretion in ewes are incomplete. The aim of the undertaken study was to determine the day/night differences in the secretion of gonadotropin releasing hormone and luteinizing hormone in follicular phase and anestrous ewes. It was demonstrated that secretion of investigated hormones is subject to diurnal and seasonal changes. The observed reduction in luteinizing hormone release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase. It could be concluded that the nocturnal suppression of luteinizing hormone secretion in follicular phase ewes may be a mechanism moving this hormone surge to the early morning.Secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) displays a circadian pattern. Data concerning differences in daily GnRH/LH secretion during different seasons in sheep are fragmentary. The aim of the study was to determine day/night differences in GnRH/LH secretion in the follicular phase and in the anestrous ewes. The studies were performed on Blackhead ewes (n = 24). Ewes from each season were divided into two groups of six animals (day and night group). The animals were euthanized 5 h after sunset or 5 h after sunrise and blood was taken to determine LH and melatonin concentrations. In the hypothalamus, the expression of GnRH and gonadotropin releasing hormone receptor (GnRHR) was determined. In the anterior pituitary, the expression of mRNA encoding subunit β of LH (LHβ) and GnRHR was assayed. Our study showed that GnRH/LH secretion is subject to diurnal and seasonal changes. The observed reduction in LH release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase, when the processes occurring at the hypothalamus are more equivocal. It could be concluded that the nocturnal suppression of LH secretion in follicular phase ewes may be a mechanism moving the LH surge to the early morning.

Highlights

  • The main neurohormone regulating the processes of reproduction is gonadotropin releasing hormone (GnRH)—a neuropeptide released in a pulsatile manner to ensure maintenance of luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from the pituitary

  • The study performed on the day-active rodent Arvicanthis niloticus showed that the LH surge occurs just before the active period, which was preceded by the accumulation of GnRH peptide in the hypothalamus [25]

  • Summarizing, our study showed that GnRH/LH secretion is subject to diurnal and seasonal changes

Read more

Summary

Introduction

As a result of evolution, animals have developed biological rhythms, thanks to which physiological processes run in a rhythmic manner. These rhythmic changes are related to changes in lighting and ambient temperature [1]. Seasonal reproduction is the consequence of profound changes in reproductive neuroendocrine activity. The regulation of reproductive activity is maintained by the hypothalamic-pituitary-gonadal axis (HPG). The main neurohormone regulating the processes of reproduction is gonadotropin releasing hormone (GnRH)—a neuropeptide released in a pulsatile manner to ensure maintenance of luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from the pituitary. GnRH is synthesized in neuros, which perikarya are, among others, in the preoptic area (POA), and a majority of these neurons send projections to the median eminence (ME), where GnRH is released [3]

Objectives
Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call