title: Effects of corticosterone pellets on baseline and stress-induced corticosterone and corticosteroid-binding-globulin.
abstract: Exogenous administration of glucocorticoids is a widely used and efficient tool to investigate the effects of elevated concentrations of these hormones in field studies. Because the effects of corticosterone are dose and duration-dependent, the exact course of plasma corticosterone levels after exogenous administration needs to be known. We tested the performance of self-degradable corticosterone pellets (implanted under the skin) in elevating plasma corticosterone levels. We monitored baseline (sampled within 3min after capture) total corticosterone levels and investigated potential interactions with corticosteroid-binding-globulin (CBG) capacity and the endogenous corticosterone response to handling in Eurasian kestrel Falco tinnunculus and barn owl Tyto alba nestlings. Corticosterone pellets designed for a 7-day-release in rodents elevated circulating baseline total corticosterone during only 2-3 days compared to placebo-nestlings. Highest levels occurred 1-2days after implantation and levels decreased strongly thereafter. CBG capacity was also increased, resulting in a smaller, but still significant, increase in baseline free corticosterone levels. The release of endogenous corticosterone as a response to handling was strong in placebo-nestlings, but absent 2 and 8 days after corticosterone pellet implantation. This indicates a potential shut-down of the hypothalamo-pituitary-adrenal axis after the 2-3 days of elevated baseline corticosterone levels. 20 days after pellet implantation, the endogenous corticosterone response to handling of nestlings implanted with corticosterone pellets attained similar levels as in placebo-nestlings. Self-degradable pellets proved to be an efficient tool to artificially elevate circulating baseline corticosterone especially in field studies, requiring only one intervention. The resulting peak-like elevation of circulating corticosterone, the concomitant elevation of CBG capacity, and the absence of an endogenous corticosterone response to an acute stressor have to be taken into account.
authors.affiliation: Swiss Ornithological Institute, Luzernerstrasse, Sempach, Switzerland. claudia.mueller@vogelwarte.ch
authors.forename: Claudia
authors.initials: C
authors.lastname: Müller
authors.forename: Bettina
authors.initials: B
authors.lastname: Almasi
authors.forename: Alexandre
authors.initials: A
authors.lastname: Roulin
authors.forename: Creagh W
authors.initials: CW
authors.lastname: Breuner
authors.forename: Susanne
authors.initials: S
authors.lastname: Jenni-Eiermann
authors.forename: Lukas
authors.initials: L
authors.lastname: Jenni
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003345:Corticosterone / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D046093:Falconiformes; D013312:Stress, Physiological / Q000502:physiology*; D020305:Strigiformes; D014156:Transcortin / Q000378:metabolism*
chemical_list: D014156:Transcortin; D003345:Corticosterone