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Biomedical subjects

A Lindahl

Publications and source records attributed to A Lindahl.

At least 73 records · Page 4Linked to original sources
PubMed1990

Human growth hormone in the blood of athymic mice grafted with cultures of hormone-secreting human keratinocytes.

An established line of human epidermal keratinocytes was permanently transformed by transfection with plasmid vectors bearing the human growth hormone gene under the control of two different promoters. Suitable selection permitted the isolation of clones secreting abundant growth hormone in culture. When such cultures were grafted to athymic mice, human growth hormone could be detected in the blood of the mice at concentrations in the physiological range for more than 4 weeks. Retrograde transfer from epithelial cells should be studied further as a possible means of introducing exogenous gene products into the circulation of humans.

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↗
PubMed1987

Effects of unilateral arterial infusion of GH and IGF-I on tibial longitudinal bone growth in hypophysectomized rats.

We have studied the effect of local arterial infusion of bacterially produced human growth hormone (hGH), insulinlike growth factor I (IGF-I), or pituitary-derived ovine prolactin (oPRL) on longitudinal bone growth of hypophysectomized rats. The substances were infused during a 14-day period by osmotic mini-pumps through a catheter which was implanted into the femoral artery of one hindlimb. Longitudinal bone growth was measured by the intravital marker tetracycline. Infusion of 1 microgram hGH per day stimulated bone growth only of the treated limb and not of the uninfused contralateral limb. Infusion of 10 micrograms hGH per day also stimulated unilateral longitudinal bone growth, but the uninfused contralateral limb also showed a significant growth response, probably because local administration of GH at this dose caused a significant elevation of GH in the systemic circulation. As a result, the differential growth response between the GH-treated and untreated limbs decreased compared to rats that were infused with 1 microgram hGH per day. Unilateral arterial infusion of 5 micrograms human IGF-I or 10 micrograms oPRL per day did not produce a significant growth response. The results of the present study confirm the observation by Schlechter and co-workers, who demonstrated that unilateral arterial infusion of GH maintained tibial cartilage width following hypophysectomy in the rat. The results of Schlechter and coworkers and the results of the present study show that GH in vivo stimulates epiphyseal cartilage growth directly. However, an increased local production of insulinlike growth factors is probably of importance for the expression of the direct effect of GH on longitudinal bone growth.(ABSTRACT TRUNCATED AT 250 WORDS)

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↗
PubMed1987

Effects of age, obesity and growth-hormone on adipogenic activity in human plasma.

The potential was examined for insulin, growth hormone and insulin-like growth factor (IGF-1) alone or in combinations to stimulate glycerophosphate dehydrogenase (GPDH) activity, a sensitive marker of differentiation of adipose precursor cells in primary culture. Insulin, but not growth hormone or IGF-1, stimulated GPDH in the presence of fetal calf serum and cat serum. The content of growth hormone in adult rat heparinised plasma seemed, however, important for such stimulation, but was also dependent on feeding status of the plasma donor, and was abolished by hypophysectomy of the cell donor. GPDH activity was then analysed in heparinised plasma in the over-night fasting state in humans to examine a potential influence of age, obesity and pregnancy. In comparison with non-obese adults, GPDH-stimulatory activity was higher in plasma from infants and small children. A similar trend was seen in plasma from teenagers. This activity was probably partly dependent on growth hormone, because this increase of activity could be inhibited by excess of anti-human growth hormone antiserum. Obesity in adulthood or among teenagers was not associated with any difference in plasma activity to stimulate cellular differentiation, and plasma from women during late pregnancy had a low stimulating capacity. Simultaneous analyses of the potential of plasma to stimulate lipid accumulation in adipose precursor cells was proportional to the triglyceride concentration. Overall, the inhibitory effect of antihuman growth hormone antiserum on the differentiating capacity of human plasma was small or non-existing. It is therefore suggested that in human plasma, factors other than growth hormone might be important for the differentiation of adipocyte precursor cells.

Adipose Tissue↗
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

Effect of insulin treatment of hypophysectomized rats on adipose tissue responsiveness to insulin and growth hormone.

The effects of insulin treatment and dietary glucose on the responsiveness of adipose tissue to insulin and GH after hypophysectomy were studied. Male rats, 130-150 g, were hypophysectomized. Glucose metabolism was measured by determining the production of CO2 from [14C]glucose and the incorporation of glucose into lipids in the epididymal fat pad. Basal levels of glucose oxidation as well as the response to insulin were markedly decreased 7 days after hypophysectomy. In hypophysectomized animals given drinking water containing 10% glucose, insulin responsiveness was partially restored, and an enhanced response to the insulin-like effect of GH was observed. Plasma insulin levels decreased after hypophysectomy. Additional glucose caused a significant increase in plasma insulin levels, but these levels were still lower than those in sham-operated animals. To examine the possibility that endogenous insulin levels are important for the capacity of adipose tissue to metabolize glucose and respond to insulin and GH, hypophysectomized rats were injected with different, progressively increasing doses of insulin for 7 days, beginning on the day after the operation. Basal levels of glucose oxidation were decreased in hypophysectomized control animals and gradually increased in a dose-dependent manner in insulin-treated animals. Basal levels were normalized when the total dose of insulin injected was 16.5 U. In these animals, the response to insulin was enhanced, and there was an increase in the magnitude of the response to GH. Similar results were obtained when glucose incorporation into lipids was determined. The decrease in basal and insulin-stimulated glucose oxidation levels after hypophysectomy were most pronounced when measured at a high glucose concentration (50 mM), when glucose transport is not rate limiting. The results indicate that the changes in glucose metabolism and hormonal responsiveness of adipose tissue after hypophysectomy are, at least in part, dependent upon the decrease in endogenous insulin levels.

Adipose Tissue↗
PubMed1983

Relationship between the biological and immunological activities of growth hormone circulating in normal rats.

The ability of GH to induce refractoriness to its own insulin-like effect in adipose tissue is highly specific for GH. Moreover, refractoriness to the insulin-like action of GH can be induced with low concentrations of GH in the range of 10 ng/ml. In the present study, the ability of plasma from normal rats to induce refractoriness to the effect of GH on the production of 14CO2 from [14C]glucose in epididymal fat pads from hypophysectomized rats was examined as a measure of a GH-specific biological effect of the plasma. Plasma levels of GH were measured by RIA. Without exception, preincubation of fat pads with plasma having immunoreactive rat GH (rGH) levels over 50 ng/ml induced refractoriness to GH, whereas plasma having immunoreactive rGH levels below 15 ng/ml did not exert this effect. In fat pads preincubated with plasma having immunoreactive rGH levels between 10-50 ng/ml, the effect of a second exposure to GH varied in a dose-dependent manner. Also, plasma pools that were diluted with buffer or plasma from hypophysectomized rats were unable to induce refractoriness when the calculated or measured levels of immunoreactive rGH were below 15 ng/ml. The results suggest that in terms of the ability of GH to induce refractoriness to the insulin-like effect of the hormone, a very good correlation exists between the biological and immunological activities of GH in plasma from normal undisturbed rats.

Adipose Tissue↗