Purification of maturational gonadotropin from Atlantic croaker (Micropogonias undulatus) and development of a homologous radioimmunoassay.

The isolation of a maturational gonadotropin from pituitaries of Atlantic croaker (Micropogonias undulatus), a marine teleost belonging to the order perciformes, is described. A radioimmunoassay has been developed for the measurement of this hormone in blood samples and validation of the assay is presented. The hormone measured is an acidic isoform of GTH and can be detected in the plasma at concentrations from 25 to 0.05 ng/ml. At least one other gonadotropic fraction was detected during the purification. The acidic form of GTH is released from croaker pituitaries after stimulation with luteinizing hormone-releasing hormone analog (LHRHa), both in vivo and in vitro. The GTH is steroidogenic, is active in an in vitro oocyte germinal-vesicle breakdown assay, and is elevated in the blood of fish undergoing LHRHa-induced ovulation.