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O G Isaksson

Publications and source records attributed to O G Isaksson.

At least 55 records · Page 3Linked to original sources
PubMed1990

Regulation by GH of insulin-like growth factor-I mRNA expression in rat epiphyseal growth plate as studied with in-situ hybridization.

Expression of insulin-like growth factor I (IGF-I) mRNA and its dependence on GH was studied in rat epiphyseal growth plate by in-situ hybridization. Methodological aspects of the technique were first evaluated on fixed sagittal cryosections from 28-day-old rat epiphyseal growth plates to ascertain specific hybridization. In-situ hybridization was compared on sections from 10- and 28-day-old rats and the GH-dependence was studied in 35-day-old hypophysectomized rats. Expression of IGF-I mRNA was apparent in chondrocytes of the proliferative, hypertrophic and early degenerative zones of the growth plate of 28-day-old rats. The epiphyseal growth plate from 10-day-old rats showed a weak hybridization signal compared with 28-day-old rats. In contrast, the mesenchymal cells of the periosteum of 10-day-old rats showed a rather strong hybridization signal. Hypophysectomy resulted in a reduction in hybridization signal and cell number of the growth plate compared with 35-day-old age-matched normal rats. GH-Replacement therapy (200 micrograms GH s.c. every 4 h for 24 h) resulted in partially restored expression of IGF-I mRNA. The present study has shown that the IGF-I gene is expressed in the rat epiphyseal growth plate chondrocytes and that the expression is dependent on GH. The results support a paracrine/autocrine role of IGF-I for the expression of the stimulatory effect of GH on longitudinal bone growth.

Animals↗
PubMed1989

Growth hormone regulates the level of insulin-like growth factor-I mRNA in rat skeletal muscle.

Levels of mRNA for the insulin-like growth factor-I (IGF-I) in rat heart and skeletal muscle and its dependence on GH were investigated using a solution hybridization assay. Levels of IGF-I mRNA decreased following hypophysectomy, and replacement therapy with human GH (hGH) normalized heart and skeletal muscle levels. The stimulatory effect of hGH was dose-dependent, the lowest effective dose being 100 micrograms. A significant increase of IGF-I mRNA was observed 60 min after s.c. administration of 100 micrograms hGH and the maximum increase was apparent 6-12 h after hGH injection. Administration of 200 micrograms IGF-I or 11 micrograms insulin did not significantly change levels of IGF-I mRNA. The results show that GH regulates the level of IGF-I mRNA in rat heart and skeletal muscle and give further support to the hypothesis that locally produced IGF-I might be a local mediator for the direct stimulatory effect of GH on the growth and development of heart and skeletal muscle.

Animals↗
PubMed1989

Demonstration of growth hormone receptors in cultured rat epiphyseal chondrocytes by specific binding of growth hormone and immunohistochemistry.

Growth hormone has been reported to exert direct effects on rat and rabbit epiphyseal chondrocytes in vitro, indicating that GH interacts with specific receptors on these cells. To investigate this possibility, binding of GH to cultured rat epiphyseal chondrocytes was studied under various experimental conditions. Chondrocytes were isolated enzymatically from epiphyseal growth plates of the proximal tibia of 20-day-old male rats and were cultured in monolayer in Ham's F-12 medium supplemented with 10% calf serum and 1% of a serum substitute. The cells were seeded at various densities (25,000-200,000 cells/well) and cultured for 5-16 days. Twenty-four hours before binding experiments, the medium containing calf serum was changed for one containing serum obtained from hypophysectomized rats, in order to avoid binding of GH present in the calf serum. Binding was studied by incubating 125I-labelled human GH (hGH) with the cells in the presence or absence of various concentrations of unlabelled hGH, bovine GH (bGH), rat GH (rGH) and ovine prolactin (oPRL). Specific binding could be demonstrated in cells cultured for 5-16 days. Binding was dependent upon time and temperature, and maximal binding was obtained by incubating the labelled hormone for 4-6 h at 24 degrees C. An increase in binding was noted between 7 and 12 days in culture. In cells cultured for 12 days, addition of unlabelled hGH, bGH or rGH caused a dose-dependent displacement of 125I-labelled hGH, whereas oPRL was ineffective. Scatchard analysis resulted in a linear plot, and the number of binding sites/cell was approximately 5700, with a dissociation constant of 0.46 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

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.

Actins↗
PubMed1988

Pulsatile intravenous growth hormone (GH) infusion to hypophysectomized rats increases insulin-like growth factor I messenger ribonucleic acid in skeletal tissues more effectively than continuous GH infusion.

In this study we have investigated a possible functional role of the plasma pattern of GH in regulation of insulin-like growth factor I (IGF-I) mRNA in liver, skeletal muscle, and rib growth plate of the rat. Hypophysectomized male rats given T4 and glucocorticoid replacement therapy were equipped with indwelling jugular venous cannulae attached via swivels to a multichannel pumping system programmed to deliver human GH in a continuous or pulsatile (one pulse per 3 h) pattern for 5 days. At the end of the experiment, skeletal muscle, rib growth plates, and liver from intact and hypophysectomized rats were homogenized, and total nucleic acid was prepared. IGF-I mRNA was quantitated by solution hybridization assay using a RNA probe radiolabeled with [35S]UTP. Pulsatile treatment with GH in a dose of 1.5 U/kg.day induced a 3- to 5-fold increase in the levels of IGF-I mRNA in skeletal muscle and rib growth plates. In contrast, continuous infusion with GH was much less effective in these tissues. In the liver both continuous and pulsatile GH infusion significantly elevated the amount of IGF-I mRNA, and there was no significant difference between these two treatments. In the tissues studied similar results were obtained with a higher dose of GH (3.0 U/kg.day). Pulsatile GH treatment stimulated longitudinal bone growth more effectively than continuous GH treatment, confirming earlier studies. It is concluded that pulsatile GH treatment is more effective than continuous GH infusion in increasing IGF-I mRNA levels in rib growth plate and skeletal muscle, i.e. two major target organs for the anabolic effects of GH.

Animals↗
PubMed1987

Differential effects of growth hormone and insulin-like growth factor I on colony formation of epiphyseal chondrocytes in suspension culture in rats of different ages.

The effect of human GH (hGH) and insulin-like growth factor I (IGF-I) on the colony formation of rat epiphyseal chondrocytes was studied in suspension culture. Chondrocytes from epiphyseal growth plates of the proximal tibia of 7-, 20-, and 28-day-old normal male rats were enzymatically isolated and cultured in the presence of 10% newborn calf serum in suspension stabilized with 0.5% agarose. The cloning efficiency (number of formed colonies per 1000 seeded cells) was 13.7 +/- 1.9, 3.2 +/- 0.6, and 3.5 +/- 0.4 for chondrocytes isolated from 7-, 20- and 28-day-old rats and cultured for 14 days, respectively. The colonies were classified according to size (colony diameter), and the number of colonies was estimated as a function of colony size (distribution of cloning efficiency). IGF-I (25-200 ng/ml) increased the total colony number among chondrocytes isolated from the three different age groups and particularly increased the number of small colonies. However, IGF-I did not significantly change the distribution of cloning efficiency as compared to the control group. hGH potentiated colony formation at concentrations of 10-80 ng/ml, but no stimulatory effect of hGH was apparent at a concentration of 160 ng/ml. GH caused an assymetric distribution of cloning efficiency that was significantly different from the control group due to an increased number of large colonies (diameter exceeding 80 microns). The differential effects of GH and IGF-I were apparent after an extended period of culture (28 days) at various concentrations of the peptides. These results show that GH as well as IGF-I induced colony formation among epiphyseal chondrocytes in suspension culture, although the effects of GH and IGF-I are different in terms of distribution of cloning efficiency. The observation that GH particularly potentiated the formation of large size colonies suggests that GH promotes the differentiation of prechondrocytes, or young chondrocytes as suggested earlier. The finding that IGF-I stimulation resulted in a higher proportion of small size chondrocyte colonies, compared to the control group, suggests that IGF-I stimulates epiphyseal chondrocytes at a later stage of differentiation.

Aging↗
PubMed1987

Growth hormone in vivo potentiates the stimulatory effect of insulin-like growth factor-1 in vitro on colony formation of epiphyseal chondrocytes isolated from hypophysectomized rats.

The effect of GH pretreatment in vivo on the colony formation of epiphyseal chondrocytes from hypophysectomized rats and the subsequent responsiveness to insulin-like growth factor (IGF-I) was studied in vitro. Chondrocytes from epiphyseal growth plates of the proximal tibia of 36-day-old hypophysectomized rats were enzymatically isolated and cultured in suspension, stabilized with agarose (0.5%) in Ham's F-12 medium and serum supplement. After 14 days the cultures were terminated and screened for cloning efficiency (number of colonies with a diameter greater than 56 microns/1000 seeded cells) and for distribution of cloning efficiency as a function of colony size. Pretreatment with human GH in vivo for 24 h (10 micrograms X 3) increased the cloning efficiency during the subsequent culture period (control, 1.5 +/- 0.1; human GH, 4.4 +/- 0.3). Addition of IGF-I to the chondrocyte cultures from control rats caused a slight increase in cloning efficiency (control, 1.5 +/- 0.1; IGF-I, 2.2 +/- 0.3) but caused a marked increase in chondrocyte cultures from GH-pretreated rats (control, 4.4 +/- 0.4; IGF-I, 8.2 +/- 0.9). The cloning efficiency was increased 12 and 24 h, but not 4 h, after start of GH-treatment in vivo. The increased responsiveness to IGF-I in vivo showed a similar time course after GH pretreatment. The distribution of cloning efficiency was altered in cultures of chondrocytes isolated from the GH-pretreated rats; large colonies were overrepresented in the GH-treated group. Colonies with a diameter exceeding 180 microns were only seen in cultures of chondrocytes isolated from the GH-pretreated animals. Addition of IGF-I in vitro did not alter the distribution of cloning efficiency, but increased the mean colony size of all colonies. Pretreatment of the rats with two different doses of IGF-I in vivo for 24 h (5 micrograms X 3 or 50 micrograms X 3) had a slight stimulatory effect on subsequent colony formation, but no potentiation of IGF-I in vitro was demonstrated. The results of the present study show that pretreatment of hypophysectomized rats with GH, but not with IGF-I, promotes the formation of chondrocyte colonies and make the chondrocytes susceptible to IGF-I in vitro. The results suggest that GH induces colony formation by IGF-I-independent mechanisms and that IGF-I is a second effector in GH action as previously shown for cultured 3T3-preadipose cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Effects of growth hormone and insulin-like growth factor-I on colony formation of rabbit epiphyseal chondrocytes at different stages of maturation.

The effect of human GH (hGH) and insulin-like growth factor-I (IGF-I) on colony formation of rabbit epiphyseal tibial chondrocytes at different stages of maturation was studied in suspension culture. The epiphyseal growth plate from the proximal tibia of 8-week-old male rabbits was dissected and divided into three different (proximal, intermediate and distal) zones, each zone representing an enrichment of chondrocytes from the germinative, proliferative and hypertrophic cell layers respectively. Chondrocytes from these three zones were isolated by collagenase digestion and cultured in the presence of 10% (v/v) newborn calf serum in suspension stabilized with 0.5% (w/v) agarose for 14 days. The colonies were classified according to diameter and the number of colonies was estimated as a function of colony size (distribution of cloning efficiency). Cell clusters with a diameter of 56 micron or more were classified as colonies. The cloning efficiency (number of colonies formed per 1000 seeded cells) was 10.1 +/- 0.7 and 6.0 +/- 0.8 for chondrocytes isolated from the proximal and intermediate zones respectively. Insulin-like growth factor-I (25-200 ng/ml) increased the number of colonies in chondrocytes isolated from the proximal zone (122 +/- 9.0-156 +/- 8.4%; control value, 100%) and from the intermediate zone (136 +/- 14.0-191 +/- 29%). Low concentrations of hGH (10-40 ng/ml) stimulated colony formation in chondrocytes isolated from the proximal zone (125 +/- 6.4-137 +/- 7.9%) whereas a high concentration of hGH (160 ng/ml) was ineffective. Chondrocytes isolated from the intermediate zone showed no response to low concentrations of hGH (10-20 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Regulation by growth hormone of number of chondrocytes containing IGF-I in rat growth plate.

Whether growth hormone stimulates longitudinal bone growth by a direct effect at the site of the growth plate or indirectly by increasing the concentration of circulating somatomedins (insulin-like growth factors) has been the subject of controversy. Immunohistochemical methods were used to explore the localization and distribution of insulin-like growth factor I (IGF-I) immunoreactivity in the epiphyseal growth plate of the proximal tibia of male rats. Cells in the proliferative zone of the growth plate of normal rats exhibited a bright immunofluorescence, whereas cells in the germinal and hypertrophic zones stained only weakly. In rats subjected to hypophysectomy, the number of fluorescent cells was markedly reduced. When the hypophysectomized rats were treated with growth hormone, either systemically or at the site of the growth plate, the number of IGF-I-immunoreactive cells in the proliferative zone was increased. The results show that IGF-I is produced in proliferative chondrocytes in the growth plate and that the number of IGF-I-containing cells is directly regulated by growth hormone. These findings suggest that IGF-I has a specific role in the clonal expansion of differentiated chondrocytes and exerts its function locally through autocrine or paracrine mechanisms.

Animals↗
PubMed1986

Effects of local administration of GH and IGF-1 on longitudinal bone growth in rats.

The effect of local administration of growth hormone (GH) and insulinlike growth factor 1 (IGF-1) on longitudinal bone growth was studied in the proximal tibia of hypophysectomized rats, by using the tetracycline method. Human GH (hGH) stimulated local bone growth when administered into the epiphysial growth plate, into the epiphysis through an implanted cannula, or into the knee joint intraarticularly. In contrast, hGH administration into the metaphysis did not cause such a stimulation. The effect of hGH was dose dependent, and the lowest daily dose of hGH that caused a stimulation was 50 ng. hGH produced by cloned bacteria was as effective as pituitary-derived hGH, excluding the possibility of a pituitary growth factor being the active compound. GH from other mammalian species (rat GH, ovine GH, and bacterially produced bovine GH) also stimulated local bone growth. Ovine prolactin (oPRL) stimulated local bone growth but the threshold dose of oPRL was approximately 100 times higher than that of hGH, suggesting that contamination of this preparation by GH may account for the stimulation. Reduced carboxymethylated human GH, that has a greatly reduced anabolic activity, did not stimulate local bone growth. Local administration of 5 micrograms of bacterially produced human IGF-1 per day produced a small but significant effect on unilateral bone growth. Simultaneous administration of hGH had no additive effect with, nor did it potentiate, the stimulatory effect of IGF-1. The present study confirms and extends earlier investigations, showing that local injection of GH at the site of the epiphysial growth plate stimulates unilateral bone growth. The study also shows that local administration of IGF-1 stimulates longitudinal bone growth.

Animals↗
PubMed1986

Growth hormone potentiates colony formation of epiphyseal chondrocytes in suspension culture.

The effect of human GH (hGH) on colony formation of rat epiphyseal plate chondrocytes was studied in suspension culture. Chondrocytes were isolated enzymatically from epiphyseal plates of the proximal tibia of 28-day-old normal male rats, and were cultured in a suspension stabilized with 0.5% agarose. After approximately 7 days of culture in the presence of 10% newborn calf serum (NCS), chondrocyte colonies developed consisting of varying numbers of cells in matrix. No colonies developed in the absence of NCS, and the number of formed colonies was proportional to the concentration of NCS (5-20%) in the medium. hGH potentiated the formation of large size colonies (diameter greater than 90 microns) after a culture period of 10 or 14 days. The lowest effective concentration of hGH was 10 ng/ml, while 40 ng/ml hGH gave a maximal stimulatory effect (40-50%). Higher concentrations of hGH (80 and 160 ng/ml) showed reduced potentiation of colony formation. The stimulatory effect of hGH was expressed at 10-15% of NCS at 14 days of culture. There was a linear relation between the number of seeded cells and the number of colonies formed, both in the absence and presence of hGH. These results show that GH potentiates colony formation in chondrocytes of the epiphyseal growth plate, providing further support for the contention that GH exert a direct stimulatory effect on epiphyseal cartilage and thus stimulates longitudinal bone growth directly. The finding that GH preferentially potentiated the formation of large size colonies suggests that GH promoted the differentiation of early proliferative chondrocytes or stem cell chondrocytes with an inherent high capacity to proliferate.

Animals↗
PubMed1985

Mode of action of pituitary growth hormone on target cells.

Normal postnatal somatic growth becomes progressively dependent on GH with time. In contrast to other hormones, GH is the only hormone known to produce a dose-dependent stimulation of postnatal growth. Most of the effects attributed to GH action appear to be the result of a direct effect of GH on cells in different peripheral tissues, including cartilage. In addition to the growth-stimulating effect, GH has the intrinsic properties of being able to exert both insulin-like and insulin-antagonistic effects in adipose tissue and skeletal muscle. These two apparently antagonistic effects seem to be explained by the stage of responsiveness of the target cells to GH, which is determined by the previous influence of endogenous GH. An inhibition of adenylate cyclase with a concomitant decrease in intracellular cAMP might be an important early cellular event in the course of GH action, but it is not known whether or how this change in nucleotide metabolism relates to the various expressed effects of the hormone. The recognition that GH directly interacts with chondrocytes in cartilage suggests that alterations in the concentration of circulating somatomedins cannot be the only factor regulating skeletal growth. The recent discovery by Green and coworkers (42) demonstrating that GH specifically stimulates the differentiation of cloned preadipose cells and myoblasts in tissue culture may be a major breakthrough in the understanding of the mechanism of action of the growth-promoting effect of GH. Green (42) has proposed that GH directly stimulates terminal differentiation of cells in many different tissues including epiphyseal plate cartilage. The finding that GH binds specifically to cells in the resting cell zone but not to differentiated chondrocytes in the growth plate suggests that prechondrocytes in the growth plate are the target cells for GH action. If it is correct that GH directly stimulates the differentiation of prechondrocytes, we suggest that, during the process of chondrocyte differentiation in the growth plate, the genes that code for growth factors of the somatomedin class, such as IGF-I, are expressed. As a consequence, the clonal expansion of the chondrocytes in the proliferative zone of the growth plate that occurs in vivo during the process of normal growth is the result of this local production of growth factors.

Animals↗
PubMed1985

Growth hormone (GH)-releasing factor (GRF) pretreatment enhances the GRF-induced GH secretion in rats with the pituitary autotransplanted to the kidney capsule.

The long term in vivo effects of the recently characterized human pancreas GH-releasing factor, hpGRF (1-44) were studied in chronically cannulated unrestrained rats. In order to minimize the influence of endogenous hypothalamic GRF and somatostatin on the pituitary, the experiments were carried out in rats with the pituitary autotransplanted to the kidney capsule. The integrated GH release (mean +/- SE) in response to an iv injection of hpGRF (4 micrograms/kg) was markedly enhanced (P less than 0.01) by iv pretreatment with hpGRF every 8 h for 3 days (182 +/- 47 h X ng/ml) as compared to saline-pretreated controls (36 +/- 4 h X ng/ml). TRH pretreatment did not potentiate the effect of hpGRF (47 +/- 9 h X ng/ml). It is concluded that multiple administrations of hpGRF enhance the GH response to a subsequent hpGRF injection in the rat. Moreover, autotransplantation of the pituitary to the kidney capsule may supply a useful in vivo model for further studies on the effects of different modes of GRF administration on GH secretion.

Animals↗
PubMed1984

Influence of gonadal steroids on age- and sex-related secretory patterns of growth hormone in the rat.

The influence of sex steroids on the pulsatile GH-secretory pattern was investigated in male and female rats of different ages. Neonatal and prepubertal gonadectomy was performed when the rats were 0-1 and 25 days old, respectively. Determinations of plasma GH levels were made in blood samples obtained from the tip of the tail or from a chronic intracardiac venous cannula. After blood sampling from the tip of the tail, maximum and minimum plasma GH levels were determined in individual rats in order to evaluate pulse height and baseline plasma GH levels. In the chronically cannulated rats the GH pulse height and plasma GH baseline levels in individual rats were determined by means of a pulse analysis computer program. Neonatal gonadectomy of male and female rats did not affect the increase in plasma GH that is observed during late prepubertal life in both sexes. However, the pulsatile, sexually differentiated, secretory pattern of GH seen in sexually mature male and female rats was modulated by gonadectomy. In adult male rats, GH was secreted in regular episodes at 3- to 4-h intervals, baseline levels being low or undetectable. After neonatal or prepubertal gonadectomy, GH baseline levels increased in comparison to the sham-operated controls. Replacement therapy with testosterone completely reversed this effect, indicating that a continuous presence of testosterone is necessary for maintaining the low baseline GH levels in adult male rats. Neonatal, but not prepubertal, gonadectomy decreased GH pulse height in male rats during adult life, suggesting that neonatal androgen secretion is a determinant for the pulse height in adult male rats. In female rats, GH pulse height was lower and baseline levels were higher than in male rats. Neonatal gonadectomy resulted in higher plasma GH pulses during puberty and decreased GH baseline levels postpubertally. There were no apparent differences in the GH-secretory patterns between male and female rats after neonatal gonadectomy. Neonatal gonadectomy of male rats decreased body weight gain as well as longitudinal bone growth, as measured in the proximal tibia by the tetracycline method. In contrast, neonatal gonadectomy of female rats resulted in a stimulation of body weight gain and longitudinal bone growth. The present results demonstrate that gonadal steroids influence GH secretion in the rat. We suggest that the sexual differentiation of the GH secretory pattern may be important for the difference in body growth between male and female rats.

Age Factors↗
PubMed1983

Specific binding of growth hormone to isolated chondrocytes from rabbit ear and epiphyseal plate.

Chondrocytes were isolated from rabbit ear, epiphyseal and rib cartilage, and their ability to bind 125I-labeled human growth hormone (hGH) was investigated. The total binding of hormone to ear chondrocytes increased with time until 4-6 h, whereas non-specific binding did not increase. Total binding was 1-3% of total counts added, and non-specific binding was 10-20% of total binding. Unlabeled hGH, bGH and oPRL competed with the binding of labeled hGH in a dose-dependent manner with half-maximal binding at concentrations of 10-20 ng/ml (hGH) and 100 ng/ml (bGH and oPRL). The two latter hormones displaced almost all specific binding of hGH at higher concentrations. Ear chondrocytes from newborn to 4 week old rabbits all showed specific binding of hGH with no clear age dependence. Rib chondrocytes, on the other hand, showed very little specific binding. Epiphyseal chondrocytes from newborn animals yielded intermediate binding values. The finding of specific hGH binding by cultured chondrocytes supports the concept of a direct effect of GH on chondrocytes.

Animals↗
PubMed1982

Growth hormone stimulates longitudinal bone growth directly.

Local administration of human growth hormone in vivo to the cartilage growth plate of the proximal tibia of hypophysectomized rats resulted in accelerated longitudinal bone growth. This finding suggests that growth hormone directly stimulates the cells in the growth plate, and does not support the theory that the increase in the plasma concentration of somatomedin that follows growth hormone administration is the cause of this stimulation.

Animals↗