Experimental Manipulation of Corticosterone Does Not Influence the Clearance Rate of Plasma Testosterone in Birds

Abstract

In vertebrates, exposure to acute stressors stimulates the secretion of adrenal glucocorticoids such as corticosterone, and in some situations this hormone plays an important role in orchestrating the trade-off that exists between reproduction and self-maintenance. Stressful conditions often lead to a decrease in plasma levels of sex steroids such as testosterone in males, and it has been hypothesized that corticosterone contributes to this decrease. Generally supporting this proposition, glucocorticoids can inhibit the reproductive axis activity at multiple levels, including direct effects on testicular endocrine function. Here we tested for the first time the additional hypothesis that stress-induced glucocorticoids are associated with an increased clearance rate of circulating testosterone. To test this hypothesis, we performed two experiments comparing changes in plasma testosterone as a function of time (6-60 min) after a single injection of this hormone into captive male house finches (Haemorhous mexicanus) that either were intact (controls) or were pharmacologically adrenalectomized by administration of the glucocorticoid synthesis inhibitor mitotane. Control finches rapidly elevated their plasma corticosterone in response to handling, whereas mitotane treatment abolished this response by approximately 95%. Contrary to our prediction, we found no clear evidence that control birds eliminated exogenous testosterone from circulation at a different rate than pharmacologically adrenalectomized finches. These findings do not support the hypothesis that, during acute stress, elevated plasma glucocorticoids stimulate the clearance rate of testosterone. The rapid inhibitory effect of stress on plasma testosterone may rather result from direct actions of glucocorticoids on the gonadal production of the androgen or involve a glucocorticoid-independent mechanism.

Wildfire affects circulating hormone levels and the expression of male sexual plumage in a tropical songbird

“…In addition, this limited sampling window could have kept us from detecting diminished fat stores following fire (Table 1). Finally, we did not find a relationship between corticosterone and testosterone in our dataset ( Figure S1), thus adding to a growing list of studies in birds suggesting an absence of antagonism between these two hormones (Davies et al 2016, Deviche et al 2017, Abolins-Abols et al 2018.…”

The effect of chronic and acute stressors, and their interaction, on testes function: an experimental test during testicular recrudescence

“…This suggests that testes in acutely stressed birds may be less sensitive to downregulation by glucocorticoids, such as corticosterone, but more sensitive to another important hormone -GnIHthat has an inhibitory effect on reproductive physiology (Tsutsui et al, 2010). Indeed, while corticosterone levels increased following the acute handling stressor (Hanauer, 2017), other studies have shown that corticosterone is unlikely to be the cause for rapid decrease in testosterone in response to acute stress in birds (Davies et al, 2016;Deviche et al 2017). Testosterone and corticosterone levels in birds are often either unrelated or positively correlated (Klukowski et al, 1997;Buchanan et al, 2003), showing that corticosterone and testosterone do not covary in a way that is consistent with testosterone suppression by corticosterone.…”

“…Testosterone levels can be suppressed by both psychological (Deviche et al, 2010;Moore and Mason, 2000) as well as physical Nelson et al, 1989) stressors. This decrease may be mediated via suppressive effects of stressors on GnRH or LH secretion (Breen and Karsch, 2006;Breen et al, 2007;Nikolarakis et al, 1986), or by direct action of components of the physiological stress response, such as the hypothalamic-pituitary-adrenal (HPA) axis, on gonads (Deviche et al, 2012(Deviche et al, , 2017Lynn et al, 2015;McGuire et al, 2013).…”

Glucocorticoids mediate egg rejection in a brood parasite host

“…Mitotane is a glucocorticoid synthesis inhibitor that has been shown to consistently reduce baseline 63 [21,22] and stress-induced [22][23][24] corticosterone levels in birds, often to non-detectable levels. We first 64 tested if the effect of mitotane on corticosterone levels in American robins parallels that seen in other 65 species.…”

“…No. 416855000, dosage 400 mg/kg), following guidelines for the maximum mitotane dosage used in 71 other species [21,22]. Four sham females were injected with a pure peanut oil vehicle (400 µl).…”