Novel function of recombinant pituitary adenylate cyclase-activating polypeptide as stimulator of innate immunity in African catfish (Clarias gariepinus) fry

There are several studies that clearly indicate a close bidirectional communication between the neuroendocrine and immune systems. In this sense, hypothalamic releasing hormones, besides their neuroendocrine role, have been shown to influence immune functions. Despite studies developed in mammals, there is, as yet, no information available about the role of the pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP-related peptide (PRP) in the fish innate immune system. The present study has evaluated the effect of PACAP and PRP administered by bath immersion, on important parameters of innate immunity and antioxidant defenses in African catfish (Clarias gariepinus) fry. We have shown, for the first time, that administration of recombinant C. gariepinus PACAP not only promotes growth but also increases lysozyme, nitric oxide synthase-derived metabolites and antioxidant defenses in treated fry. From our results, PACAP appears to act as a regulator of the teleostean immune system, in addition to its physiological role in controlling growth of fish.