A new member of the gonadotropin-releasing hormone family in teleosts: catfish gonadotropin-releasing hormone.

Two forms of immunoreactive gonadotropin-releasing hormone (GnRH) were detected in extracts of brain-pituitary tissue from the African catfish, Clarias gariepinus. Catfish I GnRH eluted first from reverse-phase HPLC and was present in larger amounts compared with catfish II GnRH. Chromatographic and immunological studies with four antisera provide evidence that catfish I GnRH is unique compared with identified GnRHs from mammal, chicken, salmon, and lamprey. Catfish II GnRH elutes in the same position as chicken II GnRH and the forms cannot yet be distinguished. GnRHs extracted from female and male catfish tissue appear to be similar in terms of the number of peaks eluted, elution position, quantity, and cross-reactivity with the antisera. The results of the HPLC and radioimmunoassay studies suggest that catfish I GnRH is likely to be 10 amino acids in length, and have an amide at the C terminus similar to the other family members. In addition, catfish I GnRH is probably different in the 5 to 10 amino acid region compared with mammalian GnRH. Finally, catfish I GnRH is likely to have a lysine or arginine residue as it is the most hydrophilic family member. The lack of the salmon form of GnRH and the presence of a unique GnRH form constitute another example of the considerable evolutionary variation that has occurred in the catfish family compared with other teleosts.