Characterization and subcellular distribution of somatogenic receptor in rat liver.
Binding of [125I]iodobovine GH [( 125I]iodo-bGH) to rat liver microsomes and Golgi/endosomal fractions isolated from male and female rats has been characterized. Binding of bGH to a pure somatogenic site was suggested by the finding that 50% inhibition of [125I]iodo-bGH binding required 5-130 ng bGH, rGH, or hGH/incubation, while around 500 ng rat PRL/incubation were needed to obtain the same effect. Binding of [125I]iodo-bGH to microsomes and Golgi/endosomes was time, temperature, and protein dependent. Maximal specific binding occurred at 15-16 and 15-20 h at 22 C in Golgi and microsomal membranes, respectively. Subcellular distribution studies demonstrated in the Golgi/endosomal fractions compared to the total particulate fraction, while residual microsomes devoid of Golgi/endosomal-derived components were approximately 2-fold enriched. Low levels of somatogenic receptors were detected in lysosome-enriched fractions. Removal of endogenous ligand by treating Golgi/endosomal membranes with 3 M MgCl2 increased specific binding of bGH about 2- to 3-fold. These results indicate that approximately 50% of specific somatogenic binding sites in the low density fractions represent internalized ligand-receptor complexes. The level of rat liver somatogenic receptors did not show a pronounced sex differentiation; however, an endocrine dependence of somatogenic receptor levels is suggested by the finding that livers from rats in the late stages of pregnancy had a level of somatogenic receptors exceeding that of nonpregnant rats.
Husman
B
B
Andersson
G
G
Norstedt
G
G
Gustafsson
J A
JA
D000818:Animals; D005260:Female; D006056:Golgi Apparatus / Q000032:analysis; D013006:Growth Hormone / Q000378:metabolism; D007457:Iodine Radioisotopes; D008099:Liver / Q000032:analysis*; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D008297:Male; D008862:Microsomes, Liver / Q000032:analysis; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000187:drug effects; D011986:Receptors, Somatotropin; D012737:Sex Factors
D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D011986:Receptors, Somatotropin; D015636:Magnesium Chloride; D013006:Growth Hormone; D008274:Magnesium