Immunomodulation by testosterone and corticosterone in toads: Experimental evidences from transdermal application.

Androgens and glucocorticoids play important roles in vertebrate's reproduction and display complex immunomodulatory functions that may affect survival. In anurans, testosterone and corticosterone are correlated to sexual behavior, reproduction, and immune function. Male toads (Rhinella jimi) were treated with acute doses of testosterone (T) and corticosterone (CORT) and immune variables (plasma bacterial killing ability [BKA], swelling after phytohemagglutinin [PHA] injection and the time point of maximum PHA swelling response) were measured. Transdermal T and CORT application increased androgen (T-DHT) and CORT plasma levels after 1 h of treatment, respectively, without a dose-specific effect. Transdermal T treatment did not affect BKA or PHA swelling response. Individuals treated with transdermal CORT showed an earlier maximum PHA swelling response and a tendency of lower BKA 15 h after treatment. Our results indicated that an acute experimental increase of CORT plasma levels diminished time for inflammatory resolution and suppressed non-cellular innate response.

Captivity effects on immune response and steroid plasma levels of a Brazilian toad (Rhinella schneideri).

Stressors can increase plasma glucocorticoid (GC) levels and decrease plasma androgen levels in different species of vertebrates. GCs can have immune-enhancing or immunosuppressive effects, which are dependent upon stress duration and intensity. The worldwide decline in amphibian populations is strongly linked to an array of different stressors. The impacts of stress on GCs, androgens, and the immune response are important to clarify and should lead to the better development of conservation strategies. The present study in adult male toads of Rhinella schneideri investigated the effects of captivity (7, 30, and 60 days) on plasma corticosterone (CORT) and plasma testosterone (T), as well as innate immune responses, specifically humoral and cell mediated responses, as indicated by bacterial killing ability (BKA) and phagocytosis by peritoneal cells, respectively. Captivity increased CORT threefold and decreased T versus controls. CORT maintained a threefold elevation throughout the captivity period, while body mass and T gradually decreased with time in captivity. BKA was lower at day 30, versus days 7 and 60, while peritoneal cell phagocytic efficiency decreased after day 30, remaining low at day 60. Moreover, phagocytosis efficiency was positively associated with T and body condition, suggesting that the effects of chronic stress on reproductive potential and immune response might be associated with the state of energetic reserves.