Experimental increase in baseline corticosterone level reduces oxidative damage and enhances innate immune response

Abstract

Glucocorticoid (GC) hormones are significant regulators of homeostasis. The physiological effects of GCs critically depend on the time of exposure (short vs. long) as well as on their circulating levels (baseline vs. stress-induced). Previous experiments, in which chronic and high elevation of GC levels was induced, indicate that GCs impair both the activity of the immune system and the oxidative balance. Nonetheless, our knowledge on how mildly elevated GC levels, a situation much more common in nature, might influence homeostasis is limited. Therefore, we studied whether an increase in GC level within the baseline range suppresses or enhances condition (body mass, hematocrit and coccidian infestation) and physiological state (humoral innate immune system activity and oxidative balance). We implanted captive house sparrows Passer domesticus with either 60 days release corticosterone (CORT) or control pellets. CORT-treated birds had elevated baseline CORT levels one week after the implantation, but following this CORT returned to its pre-treatment level and the experimental groups had similar CORT levels one and two months following the implantation. The mass of tail feathers grown during the initial phase of treatment was smaller in treated than in control birds. CORT implantation had a transient negative effect on body mass and hematocrit, but both of these traits resumed the pre-treatment values by one month post-treatment. CORT treatment lowered oxidative damage to lipids (malondialdehyde) and enhanced constitutive innate immunity at one week and one month post-implantation. Our findings suggest that a relatively short-term (i.e. few days) elevation of baseline CORT might have a positive and stimulatory effect on animal physiology.

Insulin-like growth factor 1 induces oxidative damage, but does not affect survival in a songbird

“…[17]), whereas treatment effects 146 disappeared by day 4 in our avian model, which indicates either a fast biodegradation of the 147 microspheres or a strong negative feedback in reedlings (birds). This parallels findings of 148 steady release hormone pellets that also have faster depletion in birds than in mammals [18]. 149…”

Oxidative stress and mitochondrial responses to stress exposure suggest that king penguins are naturally equipped to resist stress

“…Interestingly, similar findings in captive house sparrows linking acute restraint-stress 19 and experimental chronic elevation of GC hormones ( i.e . CORT implant) 63 to reduced oxidative damage have been recently documented. In penguins, part of this resistance to oxidative stress might be related to physiological adaptations to marine life and long-term fasting as recently shown in this species 64 .…”

Moulting season corticosterone correlates with winter season bodyweight in an Arctic migrant bird

“…A negative CORT–weight relationship has been observed in aviary enclosure tests of captive House Sparrow Passer domesticus (Vágási et al . 2018), Gambel’s White‐crowned Sparrow Zonotrichia leucophrys gambelii (Busch et al . 2008) and Starling Sturnus vulgaris (Awerman & Romero 2010).…”

“…2017, Vágási et al . 2018) but could also negatively impact, for example, future reproductive investment (Kouwenberg et al . 2013, Crossin et al .…”

“…2018, Vágási et al . 2018). In contrast, chronically elevated CORT can negatively affect overall body condition (Harms et al .…”