Detalle de: Homologous growth hormone (GH) binding in gilthead sea bream ( Sparus aurata ). Effect of fasting and refeeding on hepatic GH‐binding and plasma somatomedin‐like immunoreactivity

Specific binding of gilthead sea bream growth hormone (sbGH) to liver membrane preparations was a time and temperature dependent process, and was saturable by increasing amounts of membrane proteins. Scatchard analysis evidenced a single class of high‐affinity and lowcapacity binding sites. Ovine prolactin, recombinant tilapia prolactin, carp gonadotropin and chinook salmon gonadotropin did not compete for the 125 I‐sbGH binding sites, while recombinant trout GH, bovine GH and human GH displaced iodinated sbGH in a dose dependent‐manner. IGF‐I‐like immunoreactivity was detected after acidification of plasma and removal of IGF‐I binding activity. A parallel displacement to the rhIGF‐1 standard was observed with extracted plasma samples. Free and total hepatic GH‐binding decreased during long‐term starvation (3–9 weeks), returning to control values during the refeeding period. Plasma IGF‐I‐like immunoreactivity showed a similar trend. To our knowledge, this is the first report that indicates a coordinated regulation of GH‐binding and plasma somatomedin‐like activity in a typical marine fish.