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  • Author: L. M. Huybrechts x
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A. Vanderpooten, V. M. Darras, L. M. Huybrechts, P. Rudas, E. Decuypere and E. R. Kühn

ABSTRACT

The effects of hypophysectomy on GH binding to liver membranes of young chicks were studied 3 days and 1 week after surgery. Specific binding of 125I-labelled chicken GH (cGH) to MgCl2-treated liver microsomal fractions of hypophysectomized animals was two- to fivefold greater than to those of sham-operated or control (non-operated) birds. This effect was due to a rise in binding capacity rather than a change in binding affinity of the GH receptor. Two daily injections of cGH (20 μg/animal) returned the number of hepatic GH receptors from hypophysectomized chicks to the level of the sham-operated ones. Administration of GH to the latter group did not cause a significant lowering of specific binding or number of receptors. No positive correlation between GH binding and plasma concentrations of insulin-like growth factor-I (IGF-I) was observed; although GH binding increased, IGF-I levels were lower for the hypophysectomized group. Since the number of hepatic GH receptors and the plasma GH levels were inversely correlated, it was concluded that the GH receptors in the liver of the chicken can be down-regulated by GH. This possibly explains why GH binding is low in posthatch and young chicks, because circulating GH concentrations are high during this period.

Journal of Endocrinology (1991) 129, 275–281

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L. M. Huybrechts, D. B. King, T. J. Lauterio, J. Marsh and C. G. Scanes

ABSTRACT

The application of a human somatomedin-C radioimmunoassay for the determination of somatomedin-C in chicken plasma has been examined. Parallel inhibition of binding of 125I-labelled somatomedin-C to antisera raised against somatomedin-C was observed with acid-treated human and chicken plasma. The concentration of immunoreactive (IR)-somatomedin-C in the plasma of the domestic fowl appears to be GH dependent. Plasma concentrations of IR-somatomedin-C were reduced after hypophysectomy and partially restored by replacement therapy with chicken GH. The age/development pattern of circulating concentrations of IR-somatomedin-C has been determined in normal and dwarf strains of domestic fowl. Increases in the plasma concentration of IR-somatomedin-C were observed between 1 and 6 weeks of age in control male domestic fowl of either heavy (broiler type) or light (White Leghorn) strains. Thereafter, the plasma concentrations of IR-somatomedin-C remained constant in the heavy strain birds but declined in White Leghorn chicks. Plasma concentrations of IR-somatomedin-C were reduced in sex-linked dwarf chickens, in both light and heavy strains of fowl, but were unaffected in autosomal dwarf chickens.

J. Endocr. (1985) 104, 233–239

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J. Buyse, E. Decuypere, P. J. Sharp, L. M. Huybrechts, E. R. Kühn and C. Whitehead

ABSTRACT

Daily changes in the concentrations of plasma corticosterone, prolactin, thyroid hormones and somatomedin C were measured in 28-day-old fat and lean lines of broilers produced by selection for high and low concentrations of very low density lipoproteins (VLDL). The effects of daily injections of corticosterone on the concentrations of these hormones and on fattening were compared in the two lines. The selection procedure had no effect on the concentrations of any of the hormones. However, daily rhythms in concentrations of plasma corticosterone, tri-iodothyronine (T3) and prolactin were less often observed in the fat line than in the lean line. No differences were seen between lines in the daily rhythms in plasma thyroxine (T4) and somatomedin C. Daily injections of 2500 μg corticosterone/kg body weight, in both lines, depressed mean concentrations of plasma prolactin, T3 and somatomedin C and body weight. This dose of corticosterone also increased abdominal fat pad and liver weights expressed as a percentage of body weight. The liver and fat pad responses to 2500 μg corticosterone in both lines were greater when the steroid was injected at the end rather than towards the beginning of the 14-h daily photoperiod. There was no difference between the lines in the fattening response to corticosterone. Lower doses of 100 and 500 μg corticosterone per day did not induce fattening or affect concentrations of plasma prolactin. They did, however, depress concentrations of plasma T3. Concentrations of plasma T4 were increased in both lines treated with 2500, but not with 100 or 500 μg corticosterone, towards the beginning of the daily photoperiod. It is concluded that selection for low and high concentrations of VLDL does not affect mean levels of the hormones measured at 28 days of age or the fattening response to corticosterone. It does, however, alter the amplitude in the daily rhythm in concentrations of corticosterone, T3 and prolactin. The fattening response to corticosterone is associated with depressed concentrations of plasma prolactin, T3 and somatomedin C.

J. Endocr. (1987) 112, 229–237

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E. R. Kühn, A. Vanderpooten, L. M. Huybrechts, E. Decuypere, V. Darras and P. J. Sharp

ABSTRACT

Plasma GH, tri-iodothyronine (T3), thyroxine (T4) and liver 5′-monodeiodination (5′-D) activity were measured in 18-day-old chick embryos injected with thyrotrophin-releasing hormone (TRH) and human pancreatic growth hormone releasing factor (hpGRF). Injections of 0·1 and 1 μg TRH and 1·5 μg hpGRF increased the concentration of plasma GH while injection of 15 μg hpGRF had no effect. Concentrations of plasma T3 were raised after injection of TRH or hpGRF. Injections of TRH but not of hpGRF raised the concentration of plasma T4. The increases in concentration of plasma T3 after injection of TRH or hpGRF were parallelled by increases in liver 5′-D activity. An injection of 0·25 μg T4 significantly raised the concentration of T4 in plasma but had no effect on plasma T3 or liver 5′-D activity. It is concluded that the release of chicken GH by TRH or hpGRF is responsible for the observed increases in plasma concentration of T3 and liver 5′-D activity.

J. Endocr. (1988) 118, 233–236

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M. Tixier-Boichard, L. M. Huybrechts, E. Decuypere, E. R. Kühn, J.-L. Monvoisin, G. Coquerelle, J. Charrier and J. Simon

ABSTRACT

This study used a sex-linked dwarf mutant (SLD) chicken to evaluate growth-promoting and metabolic effects of recombinant human insulin-like growth factor-I (rhIGF-I) treatment. The SLD chicken is characterized by a 30% reduction in body weight and by high plasma GH levels, low plasma IGF-I and triiodothyronine (T3) levels and very low GH binding on liver membranes, suggesting reduced functional GH receptors compared with normal chickens. The effects of a continuous s.c. infusion by osmotic mini-pump of 0·1 mg rhIGF-I/kg per day from 4 to 8 weeks of age on body weight, bone growth and body composition were investigated in female SLD and normal chicks. In addition, half of the birds received a dietary supplement of T3 (0·1 parts per million). Plasma levels of IGF-I, GH, T3, thyroxine and insulin were followed during the treatment. In normal chicks, rhIGF-I infusion had no effect on growth and little effect on plasma hormone levels except for a decrease in plasma insulin. In dwarf chicks, rhIGF-I infusion slightly increased body weight but had no effect on longitudinal bone growth. In addition, plasma GH levels were decreased and T3 levels remained lower than in normal chicks. Normal and dwarf chicks showed a decrease in abdominal fat after both IGF-I administration and T3 supplementation, the treatments having additive effects in dwarf chicks only. The combined rhIGF-I and T3 treatment restored a quasi-normal hormonal pattern in dwarf chicks, except for insulin which remained lower than in normal chicks. These results suggest that IGF-I in the chicken has no direct endocrine effect on statural growth.

Journal of Endocrinology (1992) 133, 101–110