Somatotropic and lactotropic receptors in transgenic mice expressing human or bovine growth hormone genes.
The somatotropic and lactotropic receptors were studied in liver microsomal preparations from transgenic mice carrying the human growth hormone (hGH) or bovine growth hormone (bGH) gene fused to mouse metallothionein-I (MT) or phosphoenolpyruvate carboxykinase promoter/regulator (PEPCK). Specificity studies indicated that, similarly to normal mice, liver microsomes from the transgenic animals possess a mixed population of somatotropic and lactotropic binding sites. In transgenic animals of both sexes, the binding capacity of somatotropic receptors was significantly increased without corresponding changes in affinity. Expression of the MT-hGH hybrid gene was associated with the induction of somatotropic receptors which was approximately twice as great as that measured in animals expressing the MT-bGH hybrid gene. The binding capacity of lactotropic receptors in liver microsomes (quantitated by the use of labelled ovine prolactin) was increased 2-3 fold in transgenic females and approximately 10-fold in transgenic males as compared to the respective normal controls. We conclude that lifelong excess of GH up-regulates hepatic GH and prolactin receptors, and that lactogenic activity of GH is not essential for induction of prolactin receptors in the liver of transgenic mice.
Aguilar
R C
RC
Instituto de Quimica y Fisicoquimica Biologicas (UBA-CONICET), Facultad de Farmacia y Bioquimica, Buenos Aires, Argentina.
Fernandez
H N
HN
Dellacha
J M
JM
Calandra
R S
RS
Bartke
A
A
Ghosh
P K
PK
Turyn
D
D
D000818:Animals; D002417:Cattle; D005260:Female; D005809:Genes, Regulator; D013006:Growth Hormone / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008297:Male; D008668:Metallothionein / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D008862:Microsomes, Liver / Q000378:metabolism*; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics; D011401:Promoter Regions, Genetic; D011981:Receptors, Prolactin / Q000378:metabolism*; D011986:Receptors, Somatotropin / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012016:Reference Values; D012727:Sex Characteristics
D011981:Receptors, Prolactin; D011986:Receptors, Somatotropin; D011993:Recombinant Fusion Proteins; D013006:Growth Hormone; D008668:Metallothionein; D010729:Phosphoenolpyruvate Carboxykinase (GTP)