Prolactin and growth hormone in temperate basses (genus Morone): Purification, characterization, bioassay and reproductive effects in vivo and in vitro

Prolactin (PRL) and two variants of growth hormone (GH) were purified from pituitaries of striped bass (Morone saxatilis) and its hybrid with white bass (M. saxatilis X M. chrysops) which appear identical between species. Both GHs (I and II) appeared as single bands ({dollar}rm Msb{lcub}r{rcub} simeq 23,000{dollar}) after SDS-PAGE, as did the purified PRL (M{dollar}rmsb{lcub}r{rcub}simeq 24,000{dollar}), and the molecular weights of GH n and PRL determined by gas chromatography and mass spectrometry were 21.2 KDa and 21.3 KDa, respectively. Heterologous antisera specifically recognized Morone PRL or GH I and II in Western blots, and amino acid sequencing revealed that Morone PRL (29 residues), GH I(40 residues), and GH II (45 residues) are highly homologous to PRLs and GHs of other teleosts. Biological activity of striped bass (sb) GH II was confirmed in a heterologous in vitro assay for insulin-like growth factor mRNA production, while the biological activity of sbPRL was confirmed in a homologous in vivo hypophysectomy and prolactin replacement bioassay using fresh water-adapted, juvenile hybrid striped bass (hsb). Antisera raised against purified hsbPRL and hsbGH II immunostained white perch (M. americana) pituitary lactotrophs and somatotrophs, and was used to develop highly specific, homologous RIAs. During the reproductive cycle of striped bass, plasma PRL and GH levels were elevated during or after the spawning season, and a significant increase in mean plasma PRL was measured during final oocyte maturation (FOM) in adult, female white perch. Steroidogenic effects of hsbGH and hsbPRL on vitellogenic or preovulatory follicles from white perch were measured, and rates of germinal vesicle breakdown were altered in vitro. Our results demonstrate that PRL and GH may have important roles in Morone reproduction.