Continuous Infusion Of Growth Hormone Research Articles

Feminization of Male Mouse Liver by Persistent Growth Hormone Stimulation: Activation of Sex-Biased Transcriptional Networks and Dynamic Changes in Chromatin States.

ABSTRACTSex-dependent pituitary growth hormone (GH) secretory profiles—pulsatile in males and persistent in females—regulate the sex-biased, STAT5-dependent expression of hundreds of genes in mouse liver, imparting sex differences in hepatic drug/lipid metabolism and disease risk. Here, we examine transcriptional and epigenetic changes induced by continuous GH infusion (cGH) in male mice, which rapidly feminizes the temporal profile of liver STAT5 activity. cGH repressed 86% of male-biased genes and induced 68% of female-biased genes within 4 days; however, several highly female-specific genes showed weak or no feminization, even after 14 days of cGH treatment. Female-biased genes already in an active chromatin state in male liver generally showed early cGH responses; genes in an inactive chromatin state often responded late. Early cGH-responsive genes included those encoding two GH/STAT5-regulated transcriptional repressors: male-biased BCL6, which was repressed, and female-specific CUX2, which was induced. Male-biased genes activated by STAT5 and/or repressed by CUX2 were enriched for early cGH repression. Female-biased BCL6 targets were enriched for early cGH derepression. Changes in sex-specific chromatin accessibility and histone modifications accompanied these cGH-induced sex-biased gene expression changes. Thus, the temporal, sex-biased gene responses to persistent GH stimulation are dictated by GH/STAT5-regulated transcription factors arranged in a hierarchical network and by the dynamics of changes in sex-biased epigenetic states.

Circadian variation in the pharmacokinetics of steady state continuous subcutaneous infusion of growth hormone in adult growth hormone deficient patients

BackgroundPrevious studies in growth hormone (GH)-deficient (GHD) patients have indicated a possible diurnal variation in the pharmacokinetics (PK) of GH after subcutaneous (sc) GH administration. Thus, higher GH levels were observed during the night with continuous sc infusion, and increased GH bioavailability was reported following daily sc injections in the evening compared to morning. ObjectiveThe aim was to study whether diurnal variability in the PK of sc administered exogenous GH can be reproduced under standard conditions for all study participants, e.g. supine rest. Design and methodsEight male GHD patients (59.8±8years, body mass index 29.7±4.9kg/m2) received a continuous sc infusion of GH (3mg/24h) for 60h on two different occasions. Diurnal variation in PK of GH was studied during steady state in the last 24h of the infusion period. ResultsMedian GH levels were higher at night time (23:00h–07:00h) than during the day (10:00h–18:00h) for visit 1 [5.1 (4.5–7.2ng/ml/0.5h) vs. 4.6 (3.7–5.7ng/ml/0.5h); p<0.05], and reproducible results of diurnal GH variation were obtained during visit 2 [5.7 (4.6–7.4) ng/ml/0.5h vs. 4.6 (3.8–6.0) ng/ml/0.5h, p<0.05]. Reproducible results between days 1 and 2 were also obtained during 08:30h–20:30h and 20:30h–08:30h, respectively. ConclusionsPrevious findings of higher nocturnal GH levels were confirmed during steady state continuous sc GH infusion under standard conditions. The underlying mechanisms, e.g. whether GH absorption, distribution or elimination is primarily affected need to be further elucidated.

Unbiased, Genome-Wide In Vivo Mapping of Transcriptional Regulatory Elements Reveals Sex Differences in Chromatin Structure Associated with Sex-Specific Liver Gene Expression

We have used a simple and efficient method to identify condition-specific transcriptional regulatory sites in vivo to help elucidate the molecular basis of sex-related differences in transcription, which are widespread in mammalian tissues and affect normal physiology, drug response, inflammation, and disease. To systematically uncover transcriptional regulators responsible for these differences, we used DNase hypersensitivity analysis coupled with high-throughput sequencing to produce condition-specific maps of regulatory sites in male and female mouse livers and in livers of male mice feminized by continuous infusion of growth hormone (GH). We identified 71,264 hypersensitive sites, with 1,284 showing robust sex-related differences. Continuous GH infusion suppressed the vast majority of male-specific sites and induced a subset of female-specific sites in male livers. We also identified broad genomic regions (up to ∼100 kb) showing sex-dependent hypersensitivity and similar patterns of GH responses. We found a strong association of sex-specific sites with sex-specific transcription; however, a majority of sex-specific sites were >100 kb from sex-specific genes. By analyzing sequence motifs within regulatory regions, we identified two known regulators of liver sexual dimorphism and several new candidates for further investigation. This approach can readily be applied to mapping condition-specific regulatory sites in mammalian tissues under a wide variety of physiological conditions.

Hormonal and nutritional regulation of alternative CD36 transcripts in rat liver – a role for growth hormone in alternative exon usage

BackgroundCD36 is a multiligand receptor involved in various metabolic pathways, including cellular uptake of long-chain fatty acids. Defect function or expression of CD36 can result in dyslipidemia or insulin resistance. We have previously shown that CD36 expression is female-predominant in rat liver. In the present study, hormonal and nutritional regulation of hepatic CD36 expression was examined in male and female rats. Since alternative transcription start sites have been described in murine and human Cd36, we investigated whether alternative CD36 transcripts are differentially regulated in rat liver during these conditions.ResultsSequence information of the rat Cd36 5'-UTR was extended, showing that the gene structure of Cd36 in rat is similar to that previously described in mouse with at least two alternative first exons. The rat Cd36 exon 1a promoter was sequenced and found to be highly similar to murine and human Cd36. We show that alternative first exon usage is involved in the female-predominant expression of CD36 in rat liver and during certain hormonal states that induce CD36 mRNA abundance. Estrogen treatment or continuous infusion of growth hormone (GH) in male rats induced CD36 expression preferentially through the exon 1a promoter. Old age was associated with increased CD36 expression in male rats, albeit without any preferential first exon usage. Intermittent GH treatment in old male rats reversed this effect. Mild starvation (12 hours without food) reduced CD36 expression in female liver, whereas its expression was increased in skeletal muscle.ConclusionThe results obtained in this study confirm and extend our previous observation that GH is an important regulator of hepatic CD36, and depending on the mode of treatment (continuous or intermittent) the gene might be either induced or repressed. We suggest that the effects of continuous GH secretion in females (which is stimulatory) and intermittent GH secretion in males (which is inhibitory) explains the sex-different expression of this gene. Furthermore, a female-specific repression of hepatic CD36 in response to food deprivation was found, which was in contrast to a stimulatory effect in skeletal muscle. This demonstrates a tissue-specific regulation of Cd36.

Growth Hormone Stimulates Bone Healing in a Critical-sized Bone Defect Model

Growth hormone plays an important role in bone metabolism. Treating bone deficits is a major topic in orthopaedic surgery. Our hypothesis was that local continuous growth hormone administration stimulates bone healing in a canine critical-sized bone defect model. Bone formation in the defects was quantified using densitometric image analysis and histomorphometry. After growth hormone treatment, expression levels of insulin-like growth factors-I and II, and growth hormone receptor were determined in the bone regenerate of the original defects. Circulating plasma concentrations of insulin-like growth factors-I and II, and insulin- like growth factor binding proteins-4, and 6 were measured during treatment. Growth hormone administration resulted in healing of bone defects but without an additional effect of local infusion. Expression of insulin-like growth factor-I in the bone regenerate was lower in the growth hormone-treated dogs, whereas insulin-like growth factor-II and growth hormone receptor expression were not increased. Growth hormone increased circulating insulin-like growth factor-I and growth factor-II plasma concentrations. Continuous infusion of growth hormone stimulated bone healing in a canine critical-sized bone defect model. Local delivery of growth hormone did not additionally enhance bone healing. Increased circulating plasma concentrations of insulin-like growth factors-I and II most likely induced bone formation.

Pulsatile growth hormone secretion decreases S-adenosylmethionine synthetase in rat liver.

S-adenosylmethionine synthetase (AdoMet synthetase) is responsible for the synthesis of the major methyl donor S-adenosylmethionine. The AdoMet synthetase gene was identified by subtractive suppressive hybridization as being expressed at higher levels in the liver of rats continuously exposed to growth hormone (GH) than in rats intermittently exposed to the hormone. Further studies on the regulation of AdoMet synthetase showed that the activity and mRNA levels were higher in female than in male rats. Hypophysectomy increased AdoMet synthetase mRNA in both male and female rats. Combined thyroxine and cortisol treatment of hypophysectomized rats had no effect on AdoMet synthetase mRNA levels. Two daily injections of GH for 7 days, mimicking the male secretory pattern of GH, decreased AdoMet synthetase activity and mRNA levels. A continuous infusion of GH, mimicking the female secretory pattern of GH, had small or no effects on AdoMet synthetase activity and decreased the mRNA levels to a lesser degree than two daily injections. It is concluded that the lower AdoMet synthetase activity in male rats is due to an inhibitory effect of the male characteristic pulsatile secretory pattern of GH on AdoMet synthetase mRNA expression.

The female plasma lipoprotein pattern induced by continuous growth hormone infusion in male rats is estrogen receptor-dependent

The female plasma lipoprotein pattern induced by continuous growth hormone infusion in male rats is estrogen receptor-dependent

Sex Difference in the Daily Rhythm of Hepatic P450 Monooxygenase Activities in Rats Is Regulated by Growth Hormone Release

Daily fluctuations have been observed in the hepatic cytochrome P450 monooxygenase activities of rodents. It was confirmed in our previous study that the P450 activities assessed by measurement of 7-alkoxycoumarin O-dealkylase (ACD) showed obvious daily fluctuations in male rats with high values during the dark period. However, there is still very little information about the daily fluctuation of P450 activities in female rats. In the first experiment of the present study, the daily fluctuation of ACD activities in female rats was examined. The results indicated the absence of any apparent daily fluctuation in the hepatic ACD activities of the females, so the study confirmed a sex difference in the daily rhythm of the ACD activities. In the second experiment using hypophysectomized (Hpx) rats, it was investigated whether this sex difference in daily rhythm was attributable to growth hormone (GH) release, an activity which is known to affect the sex difference in the expression of P450 isoforms. It was found that the Hpx rats, given subcutaneous injections of GH twice during the light period to mimic a male pattern of GH secretion, showed obvious light–dark fluctuation in ACD activities with high values in the dark period, and similar results were obtained in sham-operated males. Conversely, the Hpx rats given continuous infusion of GH to mimic a female pattern of GH secretion did not show the light–dark fluctuation in ACD activities, and similar results were obtained in sham-operated females. In conclusion, there is a sex difference in the daily rhythm of the hepatic P450 activities in rats and this difference is apparently influenced by the difference in the patterns of GH secretions.

Growth hormone and insulin-like growth factor-I enhance β-glucuronidase gene activation by androgen in mouse kidney

β-Glucuronidase (GUS) is a lysosomal enzyme that, in mouse kidney, is subject to control by multiple hormones: androgen, which increases GUS transcription; estrogen, which antagonizes androgen-mediated stimulation of GUS; and growth hormone (GH), which appears to be necessary for the full androgen effect. Neither estrogen nor GH affects GUS in the absence of androgen. In hypophysectomized or pituitary dwarf mice the reduced androgen stimulation of GUS can be partially restored with GH treatment. Androgen-induced GUS mRNA increased significantly with intermittent GH, compared to no GH or continuous GH. Intact mice subjected to continuous infusion of GH showed a depressed androgen effect on GUS similar to that seen in GH-deficient mice. Thus, pulsatile GH is required for the full androgen response. Insulin-like growth factor-I (IGF-I) also restored GUS induction by androgen in GH-deficient mice. We conclude that GH enhances the effect of androgen on the GUS gene via IGF-I. Using transgenic mice, we have also identified a genetic variant of the GUS gene that is insensitive to GH enhancement of the androgen effect.

Expression of hepatocyte nuclear factor 6 in rat liver is sex-dependent and regulated by growth hormone.

Growth hormone (GH) binding to its receptor modulates gene transcription by influencing the amount or activity of transcription factors. In the rat, GH exerts sexually dimorphic effects on liver gene transcription through its pattern of secretion which is intermittent in males and continuous in females. The expression of the CYP2C12 gene coding for the female-specific cytochrome P450 2C12 protein is dependent on the continuous exposure to GH. To identify the transcription factor(s) that mediate(s) this sex-dependent GH effect, we studied the interactions of the CYP2C12 promoter with liver nuclear proteins obtained from male and female rats and from hypophysectomized animals treated or not by continuous GH infusion. GH treatment induced the binding of a protein that we identified as hepatocyte nuclear factor (HNF) 6, the prototype of a novel class of homeodomain transcription factors. HNF-6 competed with HNF-3 for binding to the same site in the CYP2C12 promoter. This HNF-6/HNF-3 binding site conveyed both HNF-6- and HNF-3-stimulated transcription of a reporter gene construct in transient cotransfection experiments. Electrophoretic mobility shift assays showed more HNF-6 DNA-binding activity in female than in male liver nuclear extracts. Liver HNF-6 mRNA was barely detectable in the hypophysectomized rats and was restored to normal levels by GH treatment. This work provides an example of a homeodomain-containing transcription factor that is GH-regulated and also reports on the hormonal regulation of HNF-6.

A Specific Loss of Growth Hormone Abolished Sex-Dependent Expression of Hepatic Cytochrome P450 in Dwarf Rats: Reversal of the Profiles by Growth Hormone-Treatment

A spontaneous dwarf rat derived from a colony of Sprague–Dawley (SD) strain has no detectable level of growth hormone (GH) in pituitary, although it contained other hormones like prolactin and ACTH. Hepatic profile of cytochrome P450 (P450) differed clearly between dwarf and normal SD rats. A male-specific form of P450, CYP2C11, was detected in dwarf male rat livers, while the level was one-third of the normal SD livers. This P450 was also detected in dwarf females. Other male-specific CYP3A2 and CYP3A18 were also contained in both sexes of dwarf rats, whereas a female-specific form, CYP2C12, was not detectable in dwarf females. Phenobarbital-inducible CYP2B1 and CYP2B2 were constitutively expressed in dwarf rats, although substantially absent in normal SD rats. To assess the role of GH on hepatic P450 expression, GH was given to dwarf rats for 7 to 9 days. The intermittent injection (mimicking the male secretory pattern) resulted in the elevation of CYP2C11 to a level as observed in normal SD males. Continuous infusion of GH (mimicking the female secretory pattern) evoked CYP2C12 in livers of both sexes of dwarf rats, whereas the treatment decreased levels of CYP3A2, CYP3A18, and CYP2B1. These results clearly demonstrate that specific defect of GH, but not pituitary, cause the clear changes in hepatic P450 forms including sex-specific forms. The present study provides evidence further to strengthen the principal role of GH on the regulation of expression of P450 in rat livers.

Which route of growth hormone administration serves best? An invited commentary.

In the 1960s pharmacotherapy with pituitary-derived human growth hormone (GH) preparations was introduced into clinics for the treatment of children with severely impaired longitudinal bone growth (1). Initially, the generally accepted route of GH administration was deep intramuscular injections. It was not until the advent of recombinant growth hormone preparations in the 1980s that subcutaneous injection of GH proved to be at least equally effective and was propagated widely (2). The less traumatic subcutaneous injection then facilitated investigation of effectiveness as a function of number of injections per week. With respect to the promotion of longitudinal bone growth in children and adolescents, daily subcutaneous injection was shown to be more effective than administration of the same weekly dose by injection thrice weekly. Extrapolation of these findings promoted further studies in animals and humans that unanimously demonstrated the superior effectivity of continuous GH infusion as compared to administration of the same dose in up to eight pulses (2. 3).

Two weeks of daily injections and continuous infusion of recombinant human growth hormone (GH) in GH-deficient adults: 1. effects on insulin-like growth factor-I (IGF-I), GH and IGF binding proteins, and glucose homeostasis

Recombinant human growth hormone (GH) is routinely administered as daily subcutaneous injections to patients with GH deficiency (GHD). However, in the hypophysectomized rat, pulsatile and continuous infusion of GH has been shown to differ in terms of the magnitude of effect on longitudinal bone growth, serum insulin-like growth factor-I (IGF-I) concentrations, and hepatic metabolism. The aim of the present study was to compare the effects of daily injections and continuous infusion of GH in GHD adults on previously well-documented GH-dependent factors. Recombinant human GH (0.25 U/kg/wk) was administered to nine men with GHD for 14 days in two different ways, ie, as a daily subcutaneous injection at 8 pm and as a continuous subcutaneous infusion, with 1 month of washout between treatments. Blood samples and tests were performed in the morning after an overnight fast before the start of GH treatment (day 0) and on day 2 and day 14 of treatment. An oral glucose tolerance test (OGTT) was performed on day 0 and day 14. Daily injections and continuous infusion of GH exerted similar effects in terms of body weight and body composition. The two modes of administration resulted in similar daily urinary GH excretion and similar serum GH concentrations in the morning. GH binding protein (GHBP) concentrations did not change significantly during the various treatment periods. Serum IGF-I and IGF-I binding protein (IGFBP)-3 concentrations increased to a greater degree during continuous infusion of GH versus daily injections. Serum IGFBP-1 concentrations decreased to a similar degree during the two modes of administration. Serum concentrations of free triiodothyronine and total triiodothyronine (T 3) increased and free thyroxine (T 4) decreased to a similar degree, independent of the mode of administration. However, total T 4 concentrations were unchanged during both modes of treatment. Serum thyrotropin (TSH) concentrations decreased during continuous infusion, and there was a similar nonsignificant decrease during daily injections of GH. Fasting free fatty acid (FFA) levels increased during treatment with one daily injection of GH, but there was no significant effect from continuous infusion. Results of measurements of fasting concentrations of blood glucose and oral glucose tolerance (OGT) indicated a more impaired glucose tolerance after daily injections of GH versus continuous infusion. In conclusion, continuous infusion and daily injections of GH have similar effects on the variables described, but the magnitude of the effects differs.

Two weeks of daily injections and continuous infusion of recombinant human growth hormone (GH) in GH-deficient adults. II. Effects on serum lipoproteins and lipoprotein and hepatic lipase activity

Recombinant human growth hormone (GH) administered as daily subcutaneous (SC) injections has been shown to affect serum lipoproteins in GH-deficient subjects. However, the effects of continuous infusion of GH on serum lipoproteins have not been investigated in GH-deficient adults. The aim of the present study was to compare effects of daily injections and continuous infusion of GH on lipoprotein metabolism. Recombinant human GH (0.25 U/kg/wk) was administered to nine GH-deficient adult men during a period of 14 days in two different ways, ie, as a daily SC injection at 8:00 pm and as a continuous SC infusion, with 1 month of washout between the treatments. Blood samples and tests were performed in the morning after an overnight fast before the start of GH treatment (day 0) and on day 2 and day 14 of treatment. Abdominal SC adipose tissue lipoprotein lipase (LPL), postheparin plasma LPL, and hepatic lipase (HL) activity were measured 120 minutes after the intake of 100 g glucose. Adipose tissue LPL activity decreased and postheparin plasma HL activity increased after 14 days of GH treatment irrespective of the mode of GH administration, whreas GH treatment had no effect on postheparin plasma LPL activity. Serum triglyceride and very-low-density lipoprotein (VLDL) triglyceride concentrations increased during GH treatment. However, VLDL triglyceride concentrations increased to a greater degree during treatment with daily GH injections than during continuous infusion of GH. Serum apolipoprotein (apo) B and low-density lipoprotein (LDL) cholesterol concentrations decreased during treatment with daily GH injections, but were not significantly affected by continuous GH infusion. Thus, apo B and LDL cholesterol concentrations were lower after daily GH injections versus continuous GH infusion. Serum lipoprotein(a) [Lp(a)] and apo E concentrations increased during both modes of GH treatment. However, continuous infusion of GH resulted in a more marked increase in Lp(a) and apo E concentrations than daily GH injections. Minor effects were observed on serum apo A-I concentrations, but high-density lipoprotein (HDL) cholesterol concentrations were not affected. In conclusion, GH treatment of GH-deficient men influenced adipose tissue LPL and postheparin plasma HL activity, as well as serum lipoprotein concentrations. Moreover, continuous GH infusion and daily GH injections differed with respect to the magnitude of effects on several lipoprotein fractions including VLDL triglycerides, LDL cholesterol, apo B, apo E, and Lp(a) concentrations.

Continuous infusion versus daily injections of growth hormone (GH) for 4 weeks in GH-deficient patients.

Endogenous GH secretion is pulsatile. Animal studies indicate that GH administered in a pulsatile manner induces growth and insulin-like growth factor I (IGF-I) generation more effectively than continuous administration. Short term human studies, however, have reported similar metabolic effects with constant and pulsatile GH delivery. This study was carried out to compare the metabolic effects of longer term continuous infusion vs. daily injections of GH. Thirteen GH-deficient patients were studied in a cross-over design. The patients were randomized to receive GH as a continuous sc infusion by means of a portable pump for 1 month and as daily sc injections (at 1900 h) for another month. An average daily GH dosage (+/- SEM) of 3.15 +/- 0.27 IU was administered during both periods. Steady state 24-h profiles of GH, IGF-I, IGF-binding proteins (IGFBPs), insulin, glucose, lipid intermediates, and other metabolites were monitored after each treatment period. At the end of each study period (at 0800 h), an oral glucose tolerance test was performed. The mean (+/- SEM) integrated levels of serum GH (micrograms per L) were higher after GH injection [2.51 +/- 0.54 (injection) vs. 1.77 +/- 0.35 (infusion); P < 0.02]. Continuous infusion induced higher nighttime than daytime GH levels (P = 0.01), indicating a diurnal variation in the absorption or clearance of GH. Serum IGF-I levels (micrograms per L) were slightly higher (P < 0.05, by analysis of variance) after continuous GH infusion [312.5 +/- 50.2 (injection) and 334.6 +/- 46.6 (infusion)]. Similarly, constant GH delivery induced higher IGFBP-3 levels (P < 0.05, by analysis of variance). Serum IGFBP-1 levels were similar on the two occasions. Daily GH injections increased daytime insulin levels (P < 0.05), whereas 24-h levels were similar (P = 0.14). The trend toward increased insulin levels after GH injections was also found during the oral glucose tolerance test (P = 0.07). Blood glucose levels were identical on the two occasions. Nocturnal levels of nonesterified fatty acids were higher (P < 0.05) after GH injection. We conclude that continuous sc infusion of GH induced serum IGF-I and IGFBP-3 levels more effectively than daily sc injections. The constant appearance of GH in the circulation did not impair glucose tolerance, but resulted in a less physiological diurnal pattern of nonesterified fatty acids. Our data do not support the concept that a pulsatile GH pattern is of critical physiological significance.

Hormonal regulation of the mRNA level of male-dominant cytochrome P450 (CYP2C27) in hamster livers

Hormonal regulation in the expression of CYP2C27, a male-predominant form of cytochrome P450 in the hamster, was investigated. The mRNA level of CYP2C27 was five-fold higher in male than in female livers. The mRNA level was suppressed by both gonadectomy and hypophysectomy in male, while the mRNA level was increased by the same treatment in female, resulting in the disappearance of sex difference. In both sexes, treatment of the gonadectomized animals with testosterone induced the cytochrome over the level of shamoperated males. Treatment of the hypophysectomized animals with testosterone elevated the level in females. On the other hand, oestradiol did not show any effects on either the gonadectomized or the hypophysectomized animals of both sexes. Twice-daily injection of growth hormone to hypophysectomized animals restored the level in males. Continuous infusion of growth hormone to hypophysectomized animals suppressed the level in both sexes. These results indicate that the expression of CYP2C27 in hamsters is under the control of endocrine factors and suggest that the gonadal-pituitary axis pathway is a control mechanism as proposed in rats and mice.

One class of growth hormone (GH) receptor and binding protein messenger ribonucleic acid in rat liver, GHR1, is sexually dimorphic and regulated by GH.

In the rat, alternatively spliced messenger RNA (mRNA) species encode GH receptor (GHR) and GH-binding protein (GHBP). Additionally, these mRNAs are alternatively spliced in the 5'-untranslated region, resulting in at least two classes of GHR and GHBP mRNA with distinct first exons and identical coding regions. These alternative first exons define two unique classes of GHR and GHBP mRNA (called GHR1 and GHR2). The GHR1 class of RNA is expressed only in the liver, is far more abundant in females than males, and is particularly abundant during pregnancy. GHR1 RNA is induced later in development than is GHR2. Additional classes of GHR and GHBP RNA may also exist. The genomic structure of the GHR1 first exon reveals a putative promotor region with no TATA box, CAAT box, or other sequence elements suggesting specific responses. An in vivo approach was used to investigate the regulation of GHR1 expression. In female rats, gonadectomy was found to reduce the percentage of steady state GHR1 RNA levels in the liver, whereas male castration resulted in an induction of GHR1 RNA. However, short-term treatment with estrogen or testosterone had little effect, suggesting that direct regulation of GHR1 expression may occur through effector(s) other than gonadal steroids. Hypophysectomy abolished GHR1 RNA in females. Treatment of hypophysectomized females and castrated males with GH by single injection did not significantly induce GHR1 RNA, but treatment by continuous infusion of GH did. Little change in non-GHR1 RNA levels was observed for each of these treatments. The results suggest that: 1) the sexual dimorphism observed in total GHR and GHBP RNA in rat liver is attributable to the sexually dimorphic expression of the GHR1 class of RNA; 2) the sexually dimorphic pattern of GH release in rats regulates the GHR1 class of RNA; 3) changes in GHR and GHBP expression observed on gonadectomy, hypophysectomy, GH treatment, and pregnancy are best attributed to GHR1 regulation; and 4) since GHR1 is liver specific, the observed increases in serum GHBP concentration in response to sex steroids, GH pattern, and pregnancy are likely to originate from the liver.

One class of growth hormone (GH) receptor and binding protein messenger ribonucleic acid in rat liver, GHR1, is sexually dimorphic and regulated by GH

In the rat, alternatively spliced messenger RNA (mRNA) species encode GH receptor (GHR) and GH-binding protein (GHBP). Additionally, these mRNAs are alternatively spliced in the 5'-untranslated region, resulting in at least two classes of GHR and GHBP mRNA with distinct first exons and identical coding regions. These alternative first exons define two unique classes of GHR and GHBP mRNA (called GHR1 and GHR2). The GHR1 class of RNA is expressed only in the liver, is far more abundant in females than males, and is particularly abundant during pregnancy. GHR1 RNA is induced later in development than is GHR2. Additional classes of GHR and GHBP RNA may also exist. The genomic structure of the GHR1 first exon reveals a putative promotor region with no TATA box, CAAT box, or other sequence elements suggesting specific responses. An in vivo approach was used to investigate the regulation of GHR1 expression. In female rats, gonadectomy was found to reduce the percentage of steady state GHR1 RNA levels in the liver, whereas male castration resulted in an induction of GHR1 RNA. However, short-term treatment with estrogen or testosterone had little effect, suggesting that direct regulation of GHR1 expression may occur through effector(s) other than gonadal steroids. Hypophysectomy abolished GHR1 RNA in females. Treatment of hypophysectomized females and castrated males with GH by single injection did not significantly induce GHR1 RNA, but treatment by continuous infusion of GH did. Little change in non-GHR1 RNA levels was observed for each of these treatments. The results suggest that: 1) the sexual dimorphism observed in total GHR and GHBP RNA in rat liver is attributable to the sexually dimorphic expression of the GHR1 class of RNA; 2) the sexually dimorphic pattern of GH release in rats regulates the GHR1 class of RNA; 3) changes in GHR and GHBP expression observed on gonadectomy, hypophysectomy, GH treatment, and pregnancy are best attributed to GHR1 regulation; and 4) since GHR1 is liver specific, the observed increases in serum GHBP concentration in response to sex steroids, GH pattern, and pregnancy are likely to originate from the liver.

The hormonal regulation of the oestrogen receptor in rat liver: an interplay involving growth hormone, thyroid hormones and glucocorticoids

The regulation of the formation of the hepatic oestrogen receptor (ER) in adult female rats was studied by assaying steady state levels of ER and ER messenger RNA under different endocrine conditions. Hypophysectomy (HX) drastically reduced ER levels from 67.5 +/- 7.9 to 8.4 +/- 0.5 (means +/- S.E.M.) fmol/mg cytosolic protein. Continuous infusion of growth hormone (GH) to HX animals tripled ER and doubled ER mRNA levels. Treatment with triiodothyronine (T3) in a high dose (10 micrograms/day) doubled ER mRNA levels. The effects of T3 were dose-dependent, since a lower dose (1 microgram/day) increased neither ER nor ER mRNA levels. ER mRNA concentrations were increased by GH to 481 +/- 44% and by T3 to 372 +/- 35% of HX control levels 4 h after single injections of the hormones in HX animals. The glucocorticoid dexamethasone (DEX) alone increased neither ER nor ER mRNA levels in HX animals. DEX and GH in combination increased ER 5-fold and ER mRNA 2-fold compared with control levels in HX animals, whereas DEX and T3 in combination increased neither ER nor ER mRNA levels. Treatment with prolactin affected neither ER nor ER mRNA levels in HX rats. Insulin-like growth factor I (IGF-I) mRNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels were measured. GAPDH mRNA levels were increased 2.5-fold in HX rats by DEX and T3 in combination and almost 2-fold by DEX and GH in combination. IGF-I mRNA levels in HX rats were increased 4.5-fold by continuous infusion of GH alone, 6-fold by GH and T3 in combination, and 2.5-fold by GH and DEX in combination. These data indicate that both GH and T3 act directly on the liver to increase ER mRNA levels. GH, the most important of these hormones, also acts at the translational and/or post-translational level to increase ER protein levels. DEX treatment suppresses the stimulatory effects of T3, but not of GH.

Administration of growth hormone (GH), but not insulin-like growth factor-I (IGF-I), by continuous infusion can induce the formation of the 150-kilodalton IGF-binding protein-3 complex in GH-deficient rats.

In the adult circulation, 70-90% of the serum insulin-like growth factors (IGFs) are carried by IGF-binding protein-3 (IGFBP-3), which exists as part of a 150-kilodalton (kDa) ternary complex including IGF and an acid-labile subunit (ALS). We have examined the hormonal regulation and molecular distribution of IGFBP-3 in the circulation of a uniquely GH-deficient (GHD) rat model. For 7 days, GHD rats were given GH by either twice daily injections (1 mg/kg) or continuous infusion (2.4 mg/kg.day) or IGF-I by continuous infusion (1.4 mg/kg.day). Each day, weight and feed and water intake were monitored, and on day 7, liver, kidney, spleen, heart, and lung were weighted, and sera were collected. Serum IGF-I was analyzed by immunoassay, and the molecular distribution of the IGFBPs was determined by neutral size-exclusion chromatography combined with Western ligand blot and Western immunoblot. The GHD rats were 40-60% lighter than their normal littermates, and all organs examined were proportionately smaller. Serum IGF-I and IGFBP-3 levels were less than 10% of those in normal rats. Incubation of serum from GHD rats with [125I]IGF-II showed that radiolabel was incorporated only into a 44-kDa IGFBP region that contained the smaller IGFBPs. IGFBP-3 eluted around 60 kDa. No 150-kDa IGFBP region was detected. The administration of GH or IGF-I to GHD rats resulted in significant increases in weight gained, although food and water intake remained unaltered. Weight gain was observed in all three treatments groups. Both GH treatment regimens significantly increased liver, spleen, and lung weight, whereas IGF-I therapy increased spleen, kidney, and heart. Administration of GH twice daily did not increase serum IGF-I or IGFBP-3 concentrations, and the molecular distribution of IGFBP-3 remained unchanged. In contrast, continuous infusion of GH resulted in 5-fold increases in serum IGF-I and increases in IGFBP-3 levels. Size-exclusion chromatography combined with Western ligand blot analysis revealed that radioligand was incorporated into 150- and 60-kDa regions, and that IGFBP-3 was detectable in both regions. Thus, GH infusion was able to induce formation of the 150-kDa ternary complex by increasing circulating levels of IGF-I, IGFBP-3, and presumably ALS. Administration of IGF-I also increased serum IGF-I and IGFBP-3 levels, although the increase in IGFBP-3 was only in the 60-kDa region of the chromatograph, suggesting that IGF-I can induce neither ALS nor formation of the 150-kDa complex.(ABSTRACT TRUNCATED AT 400 WORDS)