Does the Glucocorticoid Stress Response Make Toads More Toxic? An Experimental Study on the Regulation of Bufadienolide Toxin Synthesis.

Chemical defense is a crucial component of fitness in many organisms, yet the physiological regulation of defensive toxin synthesis is poorly understood, especially in vertebrates. Bufadienolides, the main defensive compounds of toads, are toxic to many predators and other natural enemies, and their synthesis can be upregulated by stressors, including predation risk, high conspecific density, and pollutants. Thus, higher toxin content may be the consequence of a general endocrine stress response in toads. Therefore, we hypothesized that bufadienolide synthesis may be stimulated by elevated levels of corticosterone (CORT), the main glucocorticoid hormone of amphibians, or by upstream regulators that stimulate CORT production. To test these alternatives, we treated common toad tadpoles with exogenous CORT (exoCORT) or metyrapone (MTP, a CORT-synthesis inhibitor that stimulates upstream regulators of CORT by negative feedback) in the presence or absence of predation cues for 2 or 6 days, and subsequently measured their CORT release rates and bufadienolide content. We found that CORT release rates were elevated by exoCORT, and to a lesser extent also by MTP, regardless of treatment length. Bufadienolide content was significantly decreased by treatment with exoCORT for 6 days but was unaffected by exposure to exoCORT for 2 days or to MTP for either 6 or 2 days. The presence or absence of predation cues affected neither CORT release rate nor bufadienolide content. Our results suggest that changes in bufadienolide synthesis in response to environmental challenges are not driven by CORT but may rather be regulated by upstream hormones of the stress response.

The influence of L-ascorbic acid on the antibacterial-toxic activity of aflatoxins on adsorbent layer.

AIMS: To substantiate the role of formaldehyde (HCHO) and its reaction products in the mechanism of the antibacterial-toxic effect of aflatoxins B1 (AFB1), B2, G1 and G2. MATERIALS AND RESULTS: Toxins were separated by overpressured layer chromatography, which was followed by biological evaluation directly on the adsorbent layer (BioArena system with Pseudomonas savastanoi pv. phaseolicola indicator bacteria). HCHO formed in this system was eliminated with exogenously added capturer molecule dimedone and L-ascorbic acid (AA) and measured as the adduct of dimedone and HCHO. The amount of HCHO was higher in the toxin-containing spots, particularly in the most toxic AFB1 spot, compared to a toxinless background. 0.1 mg ml(-1)AA augmented, 0.2 mg ml(-1) dimedone or 0.5 and 1 mg ml(-1) AA reduced the antibacterial effect of all four aflatoxins. CONCLUSION: The antibacterial-toxic effect of aflatoxins may be mediated by HCHO (and/or its reaction products) generated from bound HCHO forms in the bacterial cells. Basis of antibacterial-toxic activity of the four aflatoxins appears the same. SIGNIFICANCE AND IMPACT OF THE STUDY: Involvement of HCHO as a key molecule in the effect of aflatoxins indicates a totally new mechanism of action of these dangerous molecules. The BioArena system is useful to dissect the mode of action of antimicrobial compounds from different biological matrices.

Experimental training model of pancreas transplant.

UNLABELLED: Pancreas transplant (Ptx) is the gold standard for the treatment of type I diabetes, mainly when associated with renal failure. The number of Ptx is increasing worldwide, but in developing countries, such as Brazil, the number of centers is small and transplant surgeons need to practice the technique. METHODS: For this model, 21 pancreas harvestings were performed in patient corpses after death from extra-abdominal causes, without pancreatic disease and peritoneal or systemic infection. The vessels of the grafts were prepared on the backtable according to the usual practice in humans. The pancreas was implanted in the inferior vena cava and aorta of mixed breed dogs, with 10 exocrine-bladder drainage and 11 duodenum-ileal anastomosis. RESULTS: There were anastomotic strictures of the portal vein in dogs 1 and 2. There was no arterial stricture or large bleeding. None of the animals died until the revascularization of the graft. Dogs 2, 5, and 8 died during the exocrine anastomosis. The arterial flow was initially high, but at the end of the procedure there were thromboses of small arteries. CONCLUSION: The experimental surgical technique model is feasible, repeating the stages of clinical pancreatic transplantation and allowing the training of surgeons.