Decreased expression of the growth hormone receptor and growth hormone binding protein in rat liver nodules

The growth hormone receptor (GHR) and growth hormone-binding protein (GH-BP) expression were characterized in liver nodules and hepatomas from male Wistar rats. The mRNA levels of GHR and GH-BP, studied by northern blot analysis and solution hybridization, were 35-50% (in nodules) and 2-6% (in hepatomas) of the level found in liver from untreated, age-matched rats. The binding of 125I-labeled human growth hormone to a low-density membrane fraction (LDMF) containing Golgi and endosome membranes in the presence of excess ovine prolactin was 75-80% lower in nodules than in liver. When endogenous ligand was removed, the binding increased in nodules but not in liver. Affinity cross-linking experiments revealed identical specific receptor-binding protein complexes at Mr of 95,000, 55,000, and 43,000 in both nodules and liver, assuming stochiometric binding of ligand. The in vivo endocytosis of 125I-labeled bovine growth hormone correlated with the level of GH binding and was thus reduced 75-80% in nodules, compared with liver. The level of insulin-like growth factor-I (IGF-I) mRNA was reduced by 50% in nodules; however, GH administration resulted in a twofold induction of IGF-I mRNA in both nodules and liver. It is concluded that the greater proportion of occupied GHR in nodules could result from an impaired dissociation of endogenous GH, which might explain the reduced GHR mRNA expression. Furthermore the low GHR mRNA expression may reflect a de-differentiated phenotype in nodules.

Regulation of insulin-like growth factor-I and growth hormone receptor gene expression by diabetes and nutritional state in rat tissues

Insulin-like growth factor-I (IGF-I) mRNA and GH receptor mRNA levels were analysed in different tissues from rats made diabetic with streptozotocin, fasted rats and rats fed with a protein-reduced diet. Diabetes decreased IGF-I mRNA levels in liver, heart, diaphragm, kidney and aorta, but not in brain. GH receptor mRNA levels were decreased in heart and diaphragm, but not in liver and kidney. Fasting decreased IGF-I mRNA in all tissues studied except brain, and decreased GH receptor mRNA in liver, heart and diaphragm, but not in kidney. A protein-reduced diet decreased hepatic IGF-I mRNA levels but did not significantly affect other tissues, while GH receptor mRNA levels were reduced in liver and diaphragm. In conclusion, both diabetes and limited nutrition affected IGF-I and GH receptor mRNA in different tissues, but the two mRNAs were not co-ordinately regulated in all tissues studied. While reduced GH receptor gene expression may thus be responsible for decreased IGF-I gene expression in some states and tissues, additional regulatory mechanisms may be of importance.

Growth hormone regulates the rodent hepatic epidermal growth factor receptor at a pretranslational level

Recent studies have implicated the involvement of pituitary factor(s) in the regulation of hepatic epidermal growth factor receptor (EGF-R) levels. In the present study the possible role of GH as a regulator of EGF-R has been examined by measuring hepatic EGF-R mRNA and EGF binding in intact and GH-deficient rats and mice before and after administration of GH. Using a human EGF-R probe, 10.5 and 6.0 kb transcripts were detected in mouse and rat liver by Northern gel analysis. EGF-R mRNA was quantified by solution hybridization, and EGF binding determined by incubation of 125I-labelled EGF with a low-density membrane fraction. Levels of hepatic EGF-R mRNA and binding of EGF in female rats were about two-thirds of those in male rats. GH-deficient (lit/lit) male and female mice had approximately 10 and 25% respectively of the levels of EGF-R mRNA and EGF binding of intact male and female mice. Furthermore, hypophysectomized rats exhibited a reduced level of EGF-R mRNA and EGF binding, corresponding to about 20% of the levels detected in intact male rats. When hypophysectomized male and female rats received recombinant human GH (hGH) either as intermittent injections or by continuous infusion using osmotic minipumps, the EGF-R mRNA and EGF binding levels increased to about half those of the intact male animals. No differences between intermittent or continuous administration of hGH on the induction of EGF-R mRNA or EGF binding could be seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of rat growth hormone receptor gene expression

A cDNA encoding the growth hormone (GH) receptor was cloned from rat liver. Both the nucleotide and translated amino acid sequence share greater than 70% similarity with the GH receptors from rabbit and human. An RNA probe was generated from this sequence for use in a solution hybridization assay to quantitate GH receptor mRNA expression in rat tissues. Expression was detected in 9/12 tissues examined, with the highest levels observed in the liver. Expression in liver, kidney, heart and muscle was developmentally regulated, being low at birth and rising to adult levels in 5 weeks. No difference was observed between hepatic expression in males and females, although livers from pregnant rats had elevated levels. Hypophysectomy and GH treatment did not affect hepatic GH receptor mRNA levels.

Developmental and steroid hormonal regulation of insulin-like growth factor II expression

We have investigated the influence of steroid hormones on insulin-like growth factor II (IGF-II) expression. Hepatic IGF-II mRNA decreased gradually during postnatal development, reaching adult levels at 3 weeks of age. Treatment of 1-day-old rats for 4 days with 10 micrograms/day of the glucocorticoid dexamethasone (DEX) reduced IGF-II mRNA levels 10-fold in liver and inhibited body weight gain. Estradiol and testosterone did not affect IGF-II expression. A dose-response relationship between IGF-II mRNA levels and the different amounts of DEX injected was seen. IGF-II levels remained low after withdrawal of DEX, indicating an irreversible effect. Albumin expression was increased in newborn rat livers after DEX treatment. Our results suggest that glucocorticoids play an important role in the regulation of IGF-II expression. The mechanism for glucocorticoid-induced reduction of IGF-II mRNA is still unclear; however, our findings indicate that DEX inhibits IGF-II by causing premature differentiation of the liver.

Regulation of sexual differentiation in drug and steroid metabolism

Certain members of the cytochrome P-450 family are expressed at different levels in the livers of male and female rats. Although little is known of the functional significance of these sex differences, progress has been made towards the understanding of the endocrine control of hepatic sex differences in cytochrome P-450 levels. Jan-Ake Gustafsson and colleagues describe a subpopulation of hepatic sexually differentiated P-450s that is regulated by sex differences in growth hormone (GH) secretory pattern. This secretory pattern is in turn regulated by gonadal steroids. These studies demonstrate a novel action of GH and suggest that the hormonal secretory rhythm is pivotal in determination of biological effects.

Regulation of uterine insulin-like growth factor I mRNA and insulin-like growth factor II mRNA by estrogen in the rat

IGF-I and IGF-II are peptides with mitogenic properties. In this study mRNA for IGF-I and IGF-II was analysed in rat uterine tissue after different endocrine manipulations and the possibility of an estrogenic regulation of IGF expression was investigated. Both IGF-I and IGF-II mRNA were present in uterine tissue. The level of IGF-I mRNA, but not IGF-II mRNA, was reduced following ovariectomy. Administration of estradiol (2.5 micrograms/day for 4 days) to ovariectomized rats increased IGF-I mRNA 8-fold to levels seen in intact animals. In adult animals hepatic IGF-I mRNA did not appear to be increased by estrogen treatment. Low levels of IGF-II mRNA were detected in the uterus, but showed no dependence on estrogen. The inductive effect of estrogen on uterine IGF-I mRNA could not be substituted for by growth hormone administration (0.5 mg/100 g, ip for 6 h). The present results suggest IGF-I as a potential candidate for a mediator of estrogen-induced growth. Both estrogen and GH induce IGF-I mRNA and a tissue specificity for these hormones is indicated where GH regulates hepatic and estrogen uterine IGF-I mRNA.

Changes in the distribution of insulin-like growth factor I, thioredoxin, thioredoxin reductase and ribonucleotide reductase during the development of the retina

The postnatal development of the rat retina offers good opportunities to follow migration and differentiation of neuroectodermal cells. In this study we have analyzed, by immunohistochemical methods, the distribution of several protein antigens and the trophic peptide insulin-like growth factor I (IGF-I; somatomedin-C). The latter contains disulfide bonds, which in vitro are reduced by the thioredoxin system, i.e. thioredoxin, thioredoxin reductase and NADPH. Ribonucleotide reductase provides growing cells with deoxyribonucleotides, necessary for DNA synthesis, and thioredoxin is an in vitro hydrogen donor. By immunofluorescence IGF-I immunoreactivity was observed throughout the Müller neuroglial cells in the developing retina, but only to a very small extent in the mature retina. Nerve cells showed transient expression of IGF-I during their development. The IGF-I immunoreactivity is likely to be due to local synthesis, since we could demonstrate retinal IGF-I mRNA. Treatment with the transport-blocking agent colchicine caused the Müller glial cells and the retinal pigment epithelium cells to become IGF-I immunoreactive. Thioredoxin and thioredoxin reductase immunoreactivities are confined to neurons and photoreceptor cells in the developing retina. Ribonucleotide reductase subunit M1 immunoreactivity was only observed during the first postnatal week in proliferating neuroectodermal cells. In conclusion, IGF-I and ribonucleotide reductase subunit M1 immunoreactivities are transiently expressed by neuroectodermal cells in the developing rat retina. In contrast, the proteins of the thioredoxin system are demonstrable also in the mature retina.

Somatomedin C in the pancreas of young and adult, normal and obese, hyperinsulinemic mice

Immunocytochemical, immunochemical and RNA-hybridization techniques were used to map the distribution of somatomedin C (Sm-C; insulin-like growth factor I; IGF-I) in the pancreas of young and adult lean and obese mice. The D cells in the islets of Langerhans showed intense cytoplasmic Sm-C immunoreactivity, extending into their processes. Only slight Sm-C immunoreactivity was seen in A and B cells, apparently confined to the plasma membranes. In the exocrine pancreas scattered duct cells were immunopositive. Starvation increased, while feeding decreased the Sm-C immunoreactivity in B cells. RNA-hybridization analyses revealed that roughly the same number of Sm-C mRNA molecules, as calculated per DNA amount in the pancreas, could be demonstrated in young and adult, lean and obese mice. Radioimmunoassay (RIA) determinations of total Sm-C showed that there were about equal concentrations in the pancreas of lean and obese mice. There were marked differences between the liver and the pancreas, in that the RIA Sm-C values for the former were twice those in the latter while, in contrast, the corresponding values for the Sm-C mRNA, i.e. the agent determining the synthesis of Sm-C, were about 100 times higher in the liver as compared to that in the pancreas. We interpret our results as follows: The D cells in the islets form and secrete Sm-C in both young and adult, lean and obese mice, while A and B cells bind, but do not necessarily synthesize this peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of insulin-like growth factor I messenger ribonucleic acid during regeneration of rat skeletal muscle

Expression of insulin-like growth factor I (IGF-I) was studied in regenerating skeletal muscle. Irreversible damage to muscle cells was induced in the extensor digitorum longus muscle of adult rats by ischemia, preceded by glycogen depletion. IGF-I mRNA levels during the regeneration process were studied for periods up to 10 days after injury using a solution hybridization assay. Increased IGF-I mRNA levels could be demonstrated within 24 h after injury; maximum levels were achieved in 3 days and decreased to approximately normal levels by 10 days. Changes in IGF-I mRNA levels could not be seen in undamaged contralateral extensor digitorum longus muscles during the experimental period. An increase in IGF-I mRNA was also evident in injured muscles of hypophysectomized animals. In situ hybridization at the time of maximum induction showed the presence of IGF-I mRNA in proliferating myoblasts and in satellite cells. IGF-I, thus, may act as a locally produced non-GH dependent trophic factor during regeneration of skeletal muscle after injury.

Hormonal regulation of estrogen receptor messenger ribonucleic acid in T47Dco and MCF-7 breast cancer cells

Using a combination of hormone-binding assays, immunologic techniques, and mRNA hybridizations we have measured the estrogen receptor (ER) content and studied the hormonal regulation of ER mRNA in one estrogen responsive and one estrogen unresponsive breast cancer cell line, MCF-7 and T47Dco, respectively. Estradiol binding could be detected in cytosol from MCF-7 cells but not in T47Dco cells. However, when measured by an enzyme-linked immunosorbent assay, T47Dco cells were found to contain approximately 15 fmol ER/mg cytosolic protein or 10% of the ER content in MCF-7 cells. Immunologically reactive ER in T47Dco cells was indistinguishable in size (approximately equal to 68 KD) from the ER in MCF-7 cells, as shown by Western blotting using a monoclonal antihuman ER antibody. Quantification of ER mRNA in MCF-7 and T47Dco cells indicated that T47Dco cells contained approximately 50% of the ER mRNA levels found in MCF-7 cells. This basal level of ER mRNA in T47Dco cells was not decreased by estradiol treatment, as opposed to in MCF-7 cells where estradiol caused 40-60% decrease in the ER mRNA expression. Also, estradiol did not increase the progesterone receptor (PR) mRNA levels in T47Dco cells whereas in MCF-7 cells an approximately 5-fold increase of the PR mRNA levels occurred after estradiol treatment. However, incubation of the cells with the synthetic progestin R5020 decreased the ER mRNA levels to approximately the same degree in both cell lines. In conclusion, we have shown that estrogen down-regulates ER mRNA and up-regulates PR mRNA in MCF-7 cells. Neither of these estrogenic effects were seen in T47Dco cells. It appears that the steroid-resistance in T47Dco cells does not occur as a consequence of a complete absence of ER mRNA or protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular distribution of somatogenic receptors and insulin-like growth factor-I mRNA in the rat liver

Parenchymal and non-parenchymal cell fractions isolated from rat liver were analysed for the distribution of somatogenic receptors and for insulin-like growth factor-I (IGF-I) mRNA. The effect of hypophysectomy either alone or in combination with a single injection of human GH (hGH) on the levels of IGF-I mRNA was also studied in the two cell fractions. The contamination of parenchymal cells in the non-parenchymal cell fraction was in the range of 2-3%. Somatogenic receptors were found only in the parenchymal cell fraction. IGF-I mRNA was detected in both cell fractions, although the level of this mRNA was about fivefold higher in parenchymal cells. When RNA was studied by Northern gel analysis no major differences were observed in the size distribution of IGF-I transcripts in the two cell fractions. In hypophysectomized animals, the IGF-I mRNA level was decreased to 10 and 30% of control values in the parenchymal and non-parenchymal cell fractions respectively. Treatment of hypophysectomized animals with a single dose of hGH restored IGF-I mRNA in parenchymal and in non-parenchymal cells to the extent found in intact animals. In conclusion, our data indicate that somatogenic receptors are exclusively, and IGF-I mRNA predominantly, expressed in liver parenchymal cells compared with a total non-parenchymal cell fraction. The most marked effect of GH, correlating with the presence of somatogenic receptors, was seen in the parenchymal cells. The minor non-GH dependent expression of IGF-I mRNA suggests that this peptide may elicit effects in addition to the well-established GH-dependent activity.

Human calpactin II (lipocortin I) messenger ribonucleic acid is not induced by glucocorticoids

Studies were carried out to examine the effect of glucocorticoids on human calpactin II (lipocortin I) mRNA expression. A cRNA probe for human calpactin II (hCPII) was used in a solution hybridization assay to study the effect of dexamethasone on hCPII mRNA levels in human skin fibroblasts, peripheral lymphocytes, pulmonary alveolar macrophages, and HeLa S3 cells. As a positive control, human metallothionein II (hMTII) mRNA levels were measured since hMTII is known to be regulated by glucocorticoids and heavy metals, both of which induce transcriptional activity of the gene. Dexamethasone treatment of these human cell types caused a dose-dependent increase in hMTII mRNA levels, whereas no effect on hCPII mRNA levels was observed. These findings were confirmed in time course studies, where 10(-6) M dexamethasone treatment caused a maximal 2- to 5-fold increase in hMTII mRNA levels after 6-8 h of treatment but no increase in hCPII mRNA levels was observed at any time point up to 24 h. A human glucocorticoid sensitive lymphoid cell line, CEM C7, and a glucocorticoid resistant mutant, ICR-27, isolated from CEM C7, were included in order to confirm the requirement of a functional glucocorticoid receptor (GR) in the induction of glucocorticoid-regulated genes. Dexamethasone (10(-6) M) induced hMTII but not hCPII mRNA in CEM C7 cells, whereas neither hMTII nor hCPII mRNA was induced in ICR-27 cells. In conclusion, our data suggest that glucocorticoids do not induce calpactin II (lipocortin I) mRNA in the human cell types studied.

Insulin-like growth factor I in the pancreas of normal and diabetic adult rats

Insulin-like growth factor I (IGF-I, somatomedin C) was mapped by immunocytochemistry in the pancreas of normal and experimentally influenced rats. The polyclonal IGF-I antiserum K 37 was characterized and demonstrated to be specific. In the exocrine pancreas some duct cells showed IGF-I immunoreactivity, other components being negative. The three main endocrine cell types in the islets of Langerhans were IGF-I immunoreactive, most strikingly the D cells. Hypophysectomy resulted in loss of IGF-I immunoreactivity in all three endocrine cell types, i.e. D, A and B cells, while the levels of somatostatin, glucagon and insulin, respectively, remained unchanged. Starvation seemed to increase and feeding to decrease the IGF-I immunoreactivity in the B cells. Cysteamine pre-treatment reduced the normally intense IGF-I and somatostatin immunoreactivities in the D cells. In rats made diabetic with alloxan or streptozotocin, the B cells were irreversibly damaged and lost both their insulin and IGF-I immunoreactivities, while the IGF-I immunoreactivity was increased in A cells; the D cells remained unchanged. The concentrations of IGF-I mRNA in the pancreas were almost equal in normal and alloxan diabetic rats as were the concentrations of extractable IGF-I. We conclude that IGF-I immunoreactive material can be demonstrated in adult animals in all endocrine islet cells, most prominently in the D cells. The expression of IGF-I immunoreactivity is in part under pituitary control. In the adult rat only one islet cell type synthesizes IGF-I immunoreactive material, i.e. the D cells, while, in contrast, the B cells are likely to be a major IGF-I source in fetal and neonatal islets.

Regulation of insulin-like growth factor messenger ribonucleic acid in rat growth plate by growth hormone

The mechanism of action for the stimulatory effect of GH on longitudinal bone growth is not yet clarified. Several recent reports indicate that GH has a direct effect at the site of the epiphyseal growth plate, as opposed to the somatomedin hypothesis which holds that the effect of GH is mediated by circulating insulin-like growth factors (IGFs). Using a RNA probe in a solution hybridization assay we investigated the presence of IGF-I mRNA in rat rib growth plate. Hypophysectomy resulted in a decrease in the number of IGF-I mRNA copies compared to that in normal rats. Replacement treatment with GH restored the number of transcripts in a specific and dose-dependent manner. The results show that GH regulates the level of IGF-I mRNA in rat rib growth plate and give further support to the hypothesis that locally produced IGF-I might contribute to the stimulatory effect of GH on longitudinal bone growth.

Expression of insulin-like growth factor I (IGF-I) and IGF-II mRNA during hepatic development, proliferation and carcinogenesis in the rat

Insulin-like growth factor I (IGF-I) and IGF-II are peptides that presumably are required for normal fetal and postpubertal growth. The production of IGFs is developmentally regulated and the liver appears to be a major site of production. By analysing mRNA levels for IGF-I and IGF-II in the rat liver we have attempted to further study the expression of these growth factors during development and regeneration as well as during the course of hepatic carcinogenesis. Fetal livers are characterized by a high level of IGF-II mRNA and a low level of IGF-I mRNA, while in adult livers the opposite situations occur, i.e. a high level of IGF-I mRNA and a non-measurable level of IGF-II mRNA. During the course of experimentally induced hepatic cancer, IGF-I mRNA was consistently reduced and in a majority of cancers analysed (6/9) IGF-II mRNA was increased, i.e. a fetal type of IGF expression can be switched on in some experimentally induced hepatocellular carcinomas. The onset of IGF-II production during hepatic carcinogenesis appears to be a late phenomenon since liver nodules, preceding the development of hepatocellular cancer, were found not to contain IGF-II mRNA. Furthermore, during hepatic regeneration following partial hepatectomy no marked change in IGF-I or IGF-II mRNA levels was noted. The above results suggest that the fetal growth factor IGF-II could have a role in hepatic cancer.

Differing expression of insulin-like growth factor I in the developing and in the adult rat cerebellum

Insulin-like growth factor I (IGF-I; somatomedin C) is a trophic peptide of importance for the development of several tissues and organs. In the present study we have mapped the cellular distribution and dynamic changes of IGF-I immunoreactivity in the rat cerebellum from its postnatal development to maturity. In vitro hybridization of IGF-I mRNA was used to demonstrate that the IGF-I immunoreactive material was synthesized in the cerebellum during a limited time period of cerebellar differentiation. IGF-I immunoreactivity was absent in primordial nerve cells but was present in neuroglial cells during the first two days after birth and then rapidly increased in intensity in the latter during the next few days. Proliferative nerve cells in the external granular layer did not express IGF-I immunoreactivity, while migrating and differentiating nerve cells as well as neuroglial cells showed intense labelling. Starting about 2 weeks postnatally, the IGF-I immunoreactivity declined, first in the neuroglial cells and eventually in the nerve cells. No IGF-I immunoreactivity could be demonstrated in the normal adult cerebellum. Colchicine pretreatment did, however, enable demonstration of IGF-I immunoreactivity in adult cerebellar nerve cells but not in neuroglial cells. In vitro hybridization revealed IGF-I mRNA in the developing cerebellum but only at very low levels in the adult cerebellum. It is concluded that IGF-I is likely to be a factor of importance for the development and maturation of nerve cells and neuroglial cells in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone induction of insulin-like growth factor I messenger RNA in primary cultures of rat liver cells

Primary liver cells from adult rats were used to study the hormonal regulation of mRNA coding for insulin-like growth factor I (IGF-I). IGF-I mRNA could be detected at a low concentration in liver cells prepared from hypophysectomized rats and cultivated for 3 days. When these cells were exposed to GH on the second day, a dose-dependent increase in IGF-I mRNA was observed. The continuous presence of serum was not a prerequisite for this response, since GH also induced IGF-I mRNA in a defined hormone-supplemented medium. It is concluded that GH can induced IGF-I mRNA in the liver by a direct mechanism.

Induction of prolactin receptors in the liver is more closely related to the growth-promoting than to the lactogenic potency of peptides

The sex differentiated binding 125I-human prolactin (PRL) to rat liver membranes was studied and the present results extend our previous studies on induction of hepatic PRL receptors by growth hormone (GH). In prepubertal female rats, PRL receptor levels are low compared with those in mature female rat livers. Infusion of hGH during one week to 17-day-old female rats resulted in a receptor level typical of adult female rats. The time course of receptor disappearance in male rats treated with hGH was also studied. When the receptor-inducing hormone was removed, receptor levels in hGH-treated male rats returned to the normal level characteristic of male rats after approximately 96 h. The specificity of various GH-like and PRL-like hormones in PRL receptor induction was studied in hypophysectomized rats. The PRL-like hormones were identified by measuring their potency to displace 125I-hPRL from a receptor preparation obtained from female rat livers, and the GH-like hormones were identified by their potency to increase body weight in hypophysectomized rats. Using similar doses of hormones it was found that in vivo administration of growth-promoting peptides (rGH, hGH, bGH) induced PRL receptors, whereas lactogenic hormones (rPRL, hPL) had a very small or no effect on PRL receptor induction. This suggests that binding to a type of GH receptor is the first step in PRL receptor induction.

Regulation of insulin-like growth factor I gene expression by growth hormone

Recombinant clones containing exon 3 of the insulin-like growth factor I (IGF-I) gene were isolated from a mouse genomic library. These sequences were used to generate an RNA probe, which was used in a solution hybridization assay to quantitate IGF-I mRNA in various murine tissues as a function of growth hormone status. The liver is the major site of IGF-I synthesis and the level of IGF-I mRNA is regulated about 10-fold by growth hormone in the growth hormone-deficient lit/lit mouse. Nuclear run-on assays were used to show that growth hormone regulation is manifested in part at the transcriptional level. Growth hormone also affects the size distribution of hepatic IGF-I mRNAs. Pancreas showed the highest non-hepatic expression, but every tissue analyzed contained some IGF-I mRNA. Expression was not growth hormone-dependent in most non-hepatic tissues.

Effect of anterior hypothalamic deafferentation and continuous growth hormone infusion on the hepatic synthesis of alpha 2u-globulin in the male rat

Anterior hypothalamic deafferentation and infusion of human GH (hGH) in the normal male rat caused a marked reduction in the hepatic concentration of alpha 2u-globulin, an androgen-dependent protein. Although s.c. injections of hGH (twice-daily) resulted in more than a 50% reduction in the hepatic level of alpha 2u-globulin, the same dose of hGH when administered continuously through osmotic minipumps caused a threefold greater inhibition. The decreased hepatic concentration of alpha 2u-globulin after hGH administration was associated with corresponding changes in the hepatic level of translatable alpha 2u-globulin messenger RNA. Continuous infusion of hGH through osmotic minipumps and removal of the anterior hypothalamic influence on GH secretion by deafferentation also caused a marked reduction in the cytoplasmic androgen-binding activity of the rat liver. These results suggest that alterations in the level and pattern of GH secretion may influence hepatic androgen-binding activity and alpha 2u-globulin synthesis.

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.

The mode of growth hormone administration is of major importance for the excretion of the major male rat urinary proteins

Male and female urinary proteins were analysed using chromatofocusing. Male rat urine had a higher protein content (measured as UV absorbance), particularly in the pI range 5.0-5.5, where female rat urine seemed to lack UV-absorbing material. The molecular weight of the major male rat urinary protein(s) is approximately 16 000 according to sodium dodecylsulphate (SDS)-polyacrylamide gel electrophoresis. The regulation of the major male rat urinary protein(s) (pI 5.3; MRUP) was studied in normal male rats and hypophysectomized rats treated for 1 week with various hormones. Urine was collected during the last day of hormone treatment and analysed by chromatofocusing and SDS-polyacrylamide gel electrophoresis. It was found that estrogen treatment of male rats suppressed the appearance of MRUP. This 'feminizing' effect was also observed following continuous infusion for 1 week of human growth hormone (hGH) or rat growth hormone (rGH) in male rats. Single injections of hGH, however, given once daily for 1 week and supplemented with glucocorticoid, thyroid hormone and androgen had an opposite effect and induced MRUP in hypophysectomized male rats. It is concluded that the mode of administration of GH is of great importance for the effects of the hormone and that continuous, as compared to intermittent, administration of GH may result in suppression or induction, respectively, of major male rat urinary protein(s).

Growth hormone induction of lactogenic receptors at intracellular sites in male rat liver

Male and female rat livers were fractionated by density gradient centrifugation into Golgi I (mainly secretory vesicles), Golgi II (mainly cisternal elements), and lysosomes. Estimations of fraction purity and representativity were made by marker enzyme and electron microscopic analyses. The binding of [125I]iodo-human GH ( [125I]iodo-hGH) to different subcellular liver fractions were studied. In Golgi I and II the binding specificity was similar in both sexes and indicated that [125I] iodo-hGH binds to a lactogenic receptor. Scatchard analysis showed a larger number of binding sites in female Golgi I (5600 fmol/mg protein), Golgi II (3400 fmol/mg), and lysosomes (1300 fmol/mg) than in male Golgi I (240 fmol/mg), Golgi II (200 fmol/mg), and lysosomes (230 fmol/mg). The apparent dissociation constant was within a similar range (0.6-0.7 X 10(-9) M) in all fractions. Administration of hGH to male rats by continuous infusion (infusion rate, 5 micrograms/h) resulted, after 5 days of treatment, in an increase in the number of lactogenic binding sites in Golgi I and II to levels similar to the binding in the corresponding female Golgi fractions. When rat GH was given to hypophysectomized male rats (infusion rate, 10 micrograms/h) for 1 week, the binding of [125I]iodo-hGH in lysosomal and Golgi fractions was increased to a female level. The present results suggest that lactogenic receptors are located in the Golgi complex as well as the lysosomal compartment and that these receptors can be induced at these intracellular sites with both a somatotropic-lactogenic hormone (human GH) and a pure somatotropic hormone (rat GH).