Nature and distribution of gonadotropin-releasing hormone (GnRH) in the brain, and GnRH and GnRH binding activity in serum of the spotted dogfish Scyliorhinus canicula.

The distribution of different molecular forms of gonadotropin-releasing hormone (GnRH) in the brain and serum of the spotted dogfish, Scyliorhinus canicula, was investigated by an indirect immunofluorescence method, using antisera against salmon (s-), chicken-II (cII-) and mammalian (m-) GnRHs, and by reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with radioimmunoassays. Five GnRH molecular forms were demonstrated on the basis of the retention time in the RP-HPLC system. The characteristics of four of these GnRH peptides are consistent with those of m-, cII-, dogfish (df-), and sGnRH. The fifth form appears to be novel. Immunoreactive sGnRH structures were confined to the diencephalon; whereas cIIGnRH and mGnRH were found in the telencephalon and diencephalon. cIIGnRH- and dfGnRH-like molecules were detected in the serum. Moreover, a specific, low-affinity GnRH binding protein (GnRH-BP) was found in the serum of the spotted dogfish. The binding of [125I]sGnRHA to the serum GnRH-BP was dependent on incubation time, equilibrium being reached within 1 hr at 4 degrees; binding was rapid and completely reversible. Scatchard analysis yielded a linear plot with a Kd of 7.9 x 10(-7) M. The presence of a GnRH-BP in spotted dogfish serum suggests a probable action of GnRH via the general circulation.