Characterization of growth hormone binding sites in the goldfish,Carassius auratus: effects of hypophysectomy and hormone injection.

A recombinant carp growth hormone (rcGH) was used to develop for a GH radioreceptor binding assay in the goldfish (Carassius auratus). Specific binding of(125)I-rcGH to goldfish liver membranes was a pH, time, temperature, and membrane protein dependent process. Scatchard and LIGAND analysis indicated a single class of high affinity and low capacity binding site, with an association constant (Ka) of 1.9×10(10) M(-1) and a maximum binding capacity (Bmax) of 9 fmol mg(-1) protein. Liver tissue displayed the highest(125)I-rcGH binding of all the tissues examined. Displacement of(125)I-rcGH with various unlabeled teleost and mammalian GHs and prolactins revealed that the goldfish hepatic binding site was highly specific for teleost GH. Intraperitoneal administration of 0.1, 1.0, and 10 μg rcGH g(-1) body weight to hypophysectomized goldfish resulted in a 27, 52, and 68% decrease in total binding sites, respectively. Injection of a high dose of rat prolactin (rPRL) (5 μg rPRL g(-1) body weight) also resulted in a 32% decrease in total binding sites. These results suggest that endogenous GH may have a role in the regulation of its own receptors in the goldfish.