Contrasting effects of transdermal and implant corticosterone treatments in the American bullfrog wound healing

Abstract

Glucocorticoid (GC) release is triggered by adverse stimuli that activate the hypothalamus-pituitary-adrenal/interrenal axis. Glucocorticoids may enhance or suppress immune functions depending on the level of elevation. In this study, we investigated the effects of transient and chronic increase of corticosterone (CORT) on the wound healing of the American bullfrog. Frogs were submitted to a daily transdermal hormonal application that acutely elevated CORT plasma levels, or vehicle as a control. Other frogs were surgically implanted with a silastic tube filled with CORT that resulted in chronic elevation of CORT plasma levels or received empty implants as a control. A dermal biopsy was performed to create a wound and was photographed every 3 days. Individuals treated with transdermal CORT started healing faster than their control 32 days after the biopsy. Frogs that received CORT implants tended to heal slower than control subjects. Plasma bacterial killing ability was not affected by treatment, which reinforces the constitutive nature of this innate immune trait. By the end of the experiment, frogs from the acute CORT treatment had smaller wounds compared with those receiving the CORT-filled implants, highlighting the differential effects of acute (immunoenhancing) and chronic (immunosuppressive) elevation of CORT plasma levels. This article is part of the theme issue ‘Amphibian immunity: stress, disease and ecoimmunology’.

Introduction to the special issue Amphibian immunity: stress, disease and ecoimmunology

“…Regarding corticosterone experimental manipulation, [ 73 ] in this special issue shows that increase in plasma corticosterone levels by transdermal application for 48 days induced faster wound-healing when compared with controls in bullfrogs ( Lithobates catesbeianus ), pointing to the immune-enhancing effect of acute daily increases in corticosterone. The authors also show that frogs implanted with corticosterone (1 cm silastic tube filled with powdered corticosterone for 48 to 61 days) tended to heal more slowly than controls (with empty silastic tube), suggesting that the chronic increase in corticosterone can show immunosuppressive effects in these animals [ 73 ]. In addition, [ 53 ] tested the hypothesis that short- and long-term corticosterone treatment modulates the immune system in a salamander model ( N. viridescens ).…”

Phytochemicals: a promising approach to control infectious bursal disease

“…As a result, fewer antibodies are produced, cell-mediated immunity is compromised, and the body is more vulnerable to other diseases ( 41 ). The injured birds are more susceptible to secondary infections and immunosuppressive effects can last for several weeks ( 42 ). Chicken with immunosuppression and low immunity are more susceptible to disease and vaccine failure.…”