Involvement of purinergic signaling in the Amazon fish Pterygoplichthys pardalis subjected to handling stress: Relationship with immune response

Stress has a considerable impact on the welfare and productivity of fish, and stress caused by transport and handling can result in mortality rates of up to 73%. Cortisol is the major corticosteroid produced by the hypothalamic-pituitary-interrenal axis (HPI) in several stressful conditions, and high plasma cortisol levels impair immune and inflammatory responses. However, the involvement of purinergic signaling, a system that might contribute to the fine tuning of inflammatory and immune responses caused by the stress response, remains unknown in fish subjected to handling stress. Thus, the aim of this study was to evaluate the involvement of purinergic signaling with the immune response of the Amazon fish bodo (Pterygoplichthys pardalis) to acute handling stress. Plasma cortisol levels were higher 240 min post-stress in fish subjected to handling than in the control group. Plasma triphosphate diphosphohydrolase (NTPDase) activity, using adenosine triphosphate (ATP) as a substrate, was upregulated 30 min post-stress in fish subjected to handling, whereas splenic NTPDase activity was downregulated 240 min post-stress compared to the control group. No significant difference was observed between the groups regarding plasma and spleen NTPDase (using adenosine diphosphate as substrate) and 5'-nucleotidase and adenosine deaminase (ADA) activities. The levels of nitric oxide metabolites (NOx) and ATP in the spleen were higher 240 min post-stress in fish subjected to handling, although no significant difference was observed in the plasma levels. Based on these results, purinergic signaling via regulation of extracellular ATP catabolism could be involved in the immunophysiological responses of bodo subjected to acute handling stress, exerting two different profiles. In plasma, this signaling contributes to a reduction in the systemic inflammatory response, however, inhibition of ATP hydrolysis in the spleen displayed a pro-inflammatory profile due to the excessive ATP levels in the extracellular milieu, which induced the release of pro-inflammatory mediators. Thus, NTPDase activity could be a pathway associated with the immunophysiological responses of bodo to acute handling stress.