Cyclic changes in cortisol across the estrous cycle in parous and nulliparous Asian elephants

Abstract

In the context of reproduction, glucocorticoids (GCs) are generally considered to have negative effects. However, in well-studied model species, GCs fluctuate predictability across the estrous cycles, and short-term increases promote healthy ovarian function. Reproductive challenges have plagued captive elephant populations, which are not currently self-sustaining. Efforts to understand reproductive dysfunction in elephants have focused on the suppressive effects of cortisol, but the potential permissive or stimulatory effects of cortisol are unknown. In this study, we provide a detailed examination of cortisol patterns across the estrous cycle in Asian elephants (Elephas maximus). Time series analysis was used to analyze cortisol and progesterone data for a total of 73 cycles from eight females. We also compared cortisol profiles between females that successfully conceived and females that failed to conceive despite repeated mating attempts. Our results revealed that cortisol fluctuates predictably across the estrous cycle, with a peak during the second half of the follicular phase followed by low levels throughout the luteal phase. Furthermore, this pattern was significantly altered in nulliparous females; cortisol concentrations did not decline during the luteal phase to the same extent as in parous females. This study highlights the complexity of cortisol signaling and suggests future directions for understanding the role of cortisol in reproductive dysfunction.

Parasites, stress and reindeer: infection with abomasal nematodes is not associated with elevated glucocorticoid levels in hair or faeces

“…First, analysis revealed what appears to be a 21 day cyclic pattern in faecal cortisol levels that was not present in faecal corticosterone levels. Glucocorticoid levels may fluctuate in response to the oestrous cycle (von der Ohe and Servheen, 2002; Fanson et al ., 2014), which is ~20 days in reindeer (Ropstad, 2000). However, our study was conducted in summer, during anoestrus.…”

Does the degree of endocrine dyscrasia post-reproduction dictate post-reproductive lifespan? Lessons from semelparous and iteroparous species

“…In iteroparous species, chronic stresses such as starvation (caloric restriction) that moderately elevate circulating cortisol (Qiu et al 2012) extend, not shorten, lifespan. The upregulation of glucocorticoids during the estrous cycle, pregnancy, and lactation also supports a critical role for these steroids in reproductive success (Fanson et al 2014). This post-reproductive corticosteroid response also is seen in humans later in post-menopause (Rozenberg et al 1988), and has been postulated as the cause of death in other semelparous species such as the dasyurid and didelphid marsupials (Fisher et al 2013;Fisher et al 2006;Oakwood et al 2001;Schmidt et al 2006).…”

hormLong: An R package for longitudinal data analysis in wildlife endocrinology studies

“…The package includes functions allowing for exploratory graphical analysis (including mass production of longitudinal profiles, box plots, and overlaying multiple hormones), iterative baseline calculation, and AUC calculation. To demonstrate the utility of this package, we analysed a previously published hormone dataset (Fanson et al 2014). This study looked at changes in circulating cortisol across the estrous cycle (i.e., relative to progesterone) in Asian elephants.…”