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E. Decuypere and E. R. Kühn

ABSTRACT

The influence of an intravenous injection of ovine prolactin on the liver monodeiodinase activity and serum concentrations of thyroid hormones and corticosterone was studied in Hisex embryos and chicks after hatching. An injection of 1 and 10 μg ovine prolactin into 18-day-old chick embryos increased serum concentrations of tri-iodothyronine (T3) five-and eightfold respectively after 2 h. At the same time serum concentrations of thyroxine (T4) and reverse T3 (rT3) were decreased in the chick embryo, but only with 10 μg prolactin. This was accompanied by a doubling of the liver monodeiodinase activity. Serum concentrations of corticosterone, however, were not influenced by the prolactin injections. In the 5-day-old chicken, serum concentrations of T3, rT3, T4 and liver T4-5′-monodeiodinase activity were not influenced by 1 or 10 μg prolactin. Serum concentrations of corticosterone after injection of 1 or 10 μg prolactin were doubled compared with controls. These results are compatible with a prolactin-induced shift from a T4-5-monodeiodination into a T4-5′-monodeiodination in the liver at the end of incubation. This effect, however, is not mediated through a prolactin-induced corticosterone release.

J. Endocr. (1985) 104, 363–366

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E. J. Nouwen and E. R. Kühn

ABSTRACT

Adult male frogs (Rana ridibunda) were subjected to several volumetric and osmometric stimuli and the influence on circulating concentrations of arginine vasotocin (AVT) and mesotocin was studied by the use of highly specific radioimmunoassays. During progressive blood withdrawal (haemorrhage group) urine flow decreased to zero, whereas no change occurred in the plasma and urine osmolality. Control levels of 34·3±7·3 pmol AVT/1 gradually increased up to 638·3±179·1 pmol/l (P<0·001) after a blood loss of up to 50–60% of the blood volume. Plasma mesotocin concentrations also increased from 42·4±9·2 to 70·8±12·0 pmol/l (n = 7). Hypervolaemia, produced by the repeated intravenous injection of isotonic Ringer solution, increased the urine flow and osmolality compared to controls but had no influence on the plasma levels of AVT and mesotocin. Hypernatraemia without volume change profoundly increased the urine osmolality but the urine flow was not affected; the plasma concentrations of AVT and mesotocin remained at the control level. Finally, during a 1-h immobilization stress a pronounced antidiuresis occurred in the presence of a constant plasma and urine osmolality and control plasma levels of AVT and mesotocin.

It is concluded that the release of AVT and, to a smaller extent, of mesotocin is under volumetric control.

J. Endocr. (1985) 105, 371–377

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E. R. Kühn, M. Bollen and V. Darras

Pregnant rats were subcutaneously injected daily with 10 μg oestradiol benzoate (OB) and/or 1 mg bromocriptine starting on day 15 of gestation. After treatment with OB, but not bromocriptine, lower fetal body weight, fetal length and placental weight were observed. The administration of bromocriptine did not influence maternal plasma levels of prolactin, but fetal levels were decreased on day 22 of gestation. Oestradiol benzoate raised prolactin concentrations in maternal plasma on days 20 and 22, whereas fetal plasma levels were raised on day 22. This increase was counteracted by simultaneous administration of bromocriptine and OB, whereas impairment of fetal growth remained after treatment. A slight decline in fetal plasma levels of insulin was observed once, but thyroid content of triiodothyronine and thyroxine (T4) was decreased to a quarter and a third respectively of control levels in male and female fetuses of OB-treated rats, fetal circulating levels of T4 were also depressed. Maternal and fetal plasma glucose levels were decreased. A close correlation between T4 and placental or fetal weight was always present on day 22 of gestation. It was concluded that OB injected into pregnant rats will reach the fetal circulation as judged by increases in fetal plasma levels of prolactin. The observed fetal growth retardation after the OB injection was associated with thyroid deficiency, whereas plasma levels of prolactin and insulin were either not at all or only slightly altered. A direct effect of OB on placental blood flow and hence on the fetal food supply cannot, however, be excluded.

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E. J. Nouwen, E. Decuypere, E. R. Kühn, H. Michels, T. R. Hall and A. Chadwick

ABSTRACT

Serum concentrations of arginine vasotocin (AVT), mesotocin and prolactin were determined by radioimmunoassay in Rhode Island Red chickens during and after dehydration, haemorrhage and oviposition. During dehydration increased circulating levels of AVT, mesotocin and prolactin were found. As water deprivation proceeded, marked differences were observed. After an initial rise in serum AVT, mesotocin and prolactin levels during mild and moderate dehydration, concentrations of both AVT and prolactin tended to normalize during continued water deprivation, while those of mesotocin remained high throughout the whole dehydration experiment with the highest at the end of the water-deprivation period. Removal of 5 ml blood at intervals of 10 min during six consecutive time-periods did not affect serum osmolality and circulating levels of AVT and prolactin, but slightly increased mesotocin. These results suggest an osmoregulatory role for AVT and prolactin, whereas mesotocin may be involved in volume control. Finally, 1 min after oviposition, control values of 19·5 ±3·4 pmol AVT/1 (n=9) were raised more than sevenfold to 142·9±12·5 pmol/l (n=11). Thereafter, a decline occurred with a half-life for AVT of 13 min with raised serum levels up to 31 min after oviposition. In contrast, the serum concentrations of mesotocin and prolactin remained unaffected by oviposition.

J. Endocr. (1984) 102, 345–351

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R. Peeters, N. Buys, D. Vanmontfort, J. Van Isterdael, E. Decuypere and E. R. Kühn

ABSTRACT

The influence of TRH and TSH injections on plasma concentrations of tri-iodothyronine (T3) and thyroxine (T4) was investigated in neonatal (injection within 0·5 h after delivery) and growing lambs and in normal, pregnant and lactating adult ewes (all 2 years old and originating from Suffolk, Milksheep and Texal cross-breeds). Neonatal lambs had higher levels of T3, T4 and GH compared with all other groups, whereas prolactin and TSH were higher in lactating ewes. In all animals, injections of TRH increased plasma concentrations of prolactin and TSH after 15 min but not of GH at any time. Small increases in T3 and T4 were observed in neonatal lambs, without any effect on the T3 and T4 ratio, after prolactin administration, whereas prolactin did not influence plasma concentrations of T3 or T4 in all other experimental groups. Similar results for thyroid hormones were obtained after TRH or TSH injections. It was therefore concluded that the effects observed after TRH challenge were mediated by the release of TSH. With the possible exception of neonatal lambs, plasma concentrations of T3 after administration of TRH or TSH were always increased before those of T4; the increase in T3 occurred within 0·5–1 h compared with 2–4 h for T4 in all experimental groups. This resulted in an increased ratio of plasma T3 to T4 up to 4 h after injection. It is concluded that, in sheep, TRH and TSH preferentially release T3 from the thyroid gland probably by a stimulatory effect of TSH on the intrathyroidal conversion of T3 to T4.

Journal of Endocrinology (1992) 132, 93–100

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L. R. Berghman, J. van Beeumen, E. Decuypere, E. R. Kühn and F. Vandesande

ABSTRACT

The immunization of mice with an affinity-purified glycoprotein preparation from chicken pituitary tissue yielded several monoclonal antibodies towards the recently described glycosylated variant of chicken GH. As all these antibodies recognize the classical (non-glycosylated) GH molecule equally well, they provide a suitable tool for the development of both a specific immunoadsorbent and an assay method. This paper deals with the surprising purification power of the immunoadsorbent that was produced with one of the monoclonal antibodies. The resulting preparation was more than 99% pure as assessed by reversed phase high-performance liquid chromatography and sodium dodecyl sulphate-polyacrylamide gel electrophoresis, so that no further purification steps were needed before the determination of the amino acid sequence of the material. The efficiency of the purification protocol as determined by a homologous, monoclonal antibody-based radioimmunoassay was virtually absolute. Moreover, the affinity-purified GH preparation was a mixture representing the multiple molecular forms of pituitary chicken GH, including both oligomeres and glycosylated GH. The purified preparations were finally used to demonstrate the hepatic 5′-monodeiodinase-stimulating activity of GH in the chicken embryo (results not shown), in order to prove that the biological activity of the molecule had not been damaged by elution from the immunoadsorbent.

J. Endocr. (1988) 118, 381–387

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E. R. KÜHN, E. J. NOUWEN, L. NIEUWBORG, W. HEYNS and F. BERTIAU

Rats were ovariectomized 2–4 h post partum and injected with oil or 100 μg oestradiol benzoate (OB). At 65 days of age, they were decapitated at various times and circadian plasma levels of prolactin, TSH and corticosterone were measured. Rats injected with OB had a significantly raised mean concentration of plasma prolactin, whereas levels of TSH and corticosterone did not differ from those of control rats. Plasma levels of corticosterone and prolactin were positively correlated both in oil-treated controls and oestrogenized rats. A small but not significant negative correlation existed between the levels of TSH and corticosterone in oil-treated control rats. This correlation became positive in rats neonatally injected with OB. Prolactin and TSH were positively correlated in oestrogenized rats but no correlation was found in control animals. It was possible to fit the diurnal variations of all hormones in oil-treated control and OB-injected rats to a significant sinusoidal curve. The acrophase for prolactin, but not for TSH and corticosterone, shifted significantly from 22·30 h in control rats to 14·69 h in oestrogenized rats. In oil-treated control rats, the acrophases of prolactin and corticosterone differed significantly by about 12 h from the TSH peak. In rats injected neonatally with OB, however, no difference between the acrophases of the hormones was seen.

It was, therefore, possible that the shift in prolactin release and the high plasma levels were both mediated by mechanisms which are common to TSH and prolactin and whose increased susceptibility is oestrogen-dependent. The role of this abnormal phasing relationship between prolactin, corticosterone and TSH which occurred in the oestrogenized rats is discussed in relation to the high incidence of various spontaneous or induced tumours which occur during later life in these rats.

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E. R. Kühn, P. Van Osselaer, O. Siau, E. Decuypere and A. Moreels

ABSTRACT

Lambs originating from Suffolk, Milksheep and Texel crossbreeds were injected with saline, 500 μg ovine prolactin or 500 μg ovine GH within 30 min of parturition (n = 10). Birth weight was negatively correlated with plasma concentrations of reverse tri-iodothyronine (rT3) but not with thyroxine (T4), free T4 (expressed as the free thyroxine index) or cortisol. At birth, T3 and T4 plasma concentrations were high and remained high during the 3-h observation period. After 3 h a significantly lower rT3 concentration was found. The cortisol concentration at birth was also high (100–400 nmol/l) but decreased rapidly to basal values after 1 h. An injection of 500 μg prolactin after parturition did not influence the hormonal parameters studied except for rT3 where, after 2 h, lower plasma concentrations were found compared with controls.

Growth hormone raised T3 levels from 4·80 ± 0·44 (s.e.m.) nmol/l at birth to 6·74 ± 0·42 nmol/l at 1 h after birth (P < 0·01) and to 6·51 ± 0·42 nmol/l after 2 h (P < 0·05). At both times these values were significantly (P < 0·001) different from saline-injected controls. GH decreased rT3 from 6·77 ± 0·71 nmol/l at birth to 5·42 ± 0·54 nmol/l after 1 h (P < 0·05) and to 5·10 ± 0·45 nmol/l after 2 h (P < 0·01; values were also significantly different from saline controls at P < 0·05 and < 0·005 respectively). At the same time total and free T4 concentrations were increased. No influence of prolactin or GH injection on plasma cortisol concentrations was seen. It is concluded that GH may play an important role in the maturation of thyroid functions during the perinatal period of lambs by increasing T4 secretion and by increasing the conversion of T4 to T3 and decreasing the T4 to rT3 conversion rates.

J. Endocr. (1986) 109, 215–219

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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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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