Episodic and seasonal rhythms of cortisol secretion in male Eld's deer (Cervus eldi thamin)

Abstract

Episodic and seasonal rhythms of cortisol secretion were evaluated in six adult Eld's deer (Cervus eldi thamin) stags. Plasma cortisol was measured in serial blood samples collected via remote catheterization every 10 min for 10 h within 2 weeks of the summer solstice (21 June), autumn equinox (22 September), winter solstice (21 December) and spring equinox (20 March), and in weekly blood samples collected from sedated stags. Cortisol was secreted episodically at a rate of approximately 0.6 peaks/h. Based on quantitative peak detection analyses of each 10-h data series, no overall seasonal differences (P > 0.05) were detected in the number of peaks (mean range, 5.7-6.2), maximal peak height (mean range, 30.1-40.8 nmol/l), mean peak height as per cent increase (mean range, 158-168%), mean interval between peaks (mean range, 80.1-88.6 min), mean peak width (mean range, 55.1-65.1 min) and mean peak area under the curve (mean range, 675-816 nmol/l min). Based on weekly blood sampling, spring cortisol concentrations were elevated (P < 0.05) compared with summer and autumn concentrations. However, when mean cortisol concentrations derived from the 10-h quarterly data sets were analysed, no seasonal differences (P > 0.05) were detected. The present study represents the first detailed confirmation of episodic cortisol secretion in any cervid. Results (1) indicate that Eld's deer stags lack a distinct seasonal rhythm of cortisol secretion and (2) clearly illustrate the need for frequent blood sampling in fully conscious individuals to ensure accurate assessment of adrenal status in cervids.

Ultradian, circadian and seasonal rhythms in cortisol secretion and adrenal responsiveness to ACTH and yarding in unrestrained red deer (Cervus elaphus) stags

“…Significant pulses in cortisol concentration occurred on average every 72 min, a frequency (0·8 peaks/h) similar to that reported for Eld's deer (0·6 peaks/h (Monfort et al 1993)), and other ruminant species including cattle (0·5 peaks/h (Ladewig & Schmidt 1989, Lefcourt et al 1993), sheep (0·8-1·2 peaks/h (Fulkerson & Tang 1979)) and non ruminant species such as the horse (0·6 peaks/h (Irvine & Alexander 1994)). This pulsatile release of cortisol during periods of normal undisturbed activity may function to prevent down regulation of the adrenal axis, thereby maintaining the ability of the axis to respond maximally to stressors.…”

“…Studies in a variety of species including human (Veldhuis et al 1990), cattle (Ladewig & Smidt 1989), sheep (Kennaway et al 1981) and deer (Monfort et al 1993) have shown that the HPA axis exhibits variations over time in basal activity and responsiveness, distinct from that following the imposition of a stressor. This variation can form a consistent rhythm which fluctuates within or about 24 h (ultradian and circadian rhythms respectively) or can be of longer duration, with variations occurring on an annual basis (seasonal or circannual rhythms).…”

“…Such pulsatile secretion is thought to prevent down-regulation of the HPA axis while maintaining its ability to respond to stress (Monfort et al 1993). In deer, episodic secretion of cortisol, the predominant glucocorticoid (van Mourik et al 1985, Smith & Bubenik 1990, has been investigated in Eld's deer (Cervus eldi thamin) (Monfort et al 1993) but there appears to be no information on cortisol secretory dynamics in red deer (Cervus elaphus).…”

“…This rhythm is entrained by feeding (Saito et al 1989) and activity/sleep wake cycles (Born et al 1997). There is no evidence from studies of deer for a circadian rhythm in HPA axis activity (white-tailed deer (Odocoileus virginianus) (Bubenik et al 1983); rusa deer (Cervus timorensis) (van Mourik & Stelmasiak 1984); Eld's deer (Monfort et al 1993)). However, in these studies the deer were subjected to either handling or indoor housing, factors known to attenuate circadian rhythms in other species (Irvine & Alexander 1994).…”

“…Evidence for a seasonal rhythm in adrenal activity or responsiveness in deer varies between species and studies, with seasonal changes reported in white-tailed deer (Bubenik et al 1983), reindeer (Rangifer tarandus) (Nilssen et al 1985), axis deer (Axis axis) (Chapple et al 1991) and red deer (Suttie et al 1995, Cassidy 1996 but not in Eld's deer (Monfort et al 1993) or in another study on axis deer (Bubenik & Brown 1989).…”