bluuebunny/crossref_metadata_2025_split huggingface dataset:
Suppression of LH secretion in food-restricted lactating females: effects of ovariectomy and bromocryptine treatment
Authors: Walker C-D , Mitchell J B , Woodside B C 
Published: December 2008

Abstract
It has been shown that restricting food in lactating rats for the first 2 weeks postpartum at a level of 60% of the ad-libitum daily ration increases the length of lactational dioestrus by about 7 days but little is known about correlated changes in hormone levels. In the first experiment we report changes in LH, prolactin (PRL) and ACTH secretion in food-restricted and ad-libitum fed lactating rats at various stages of lactation. Our results demonstrate that food restriction during the first 2 weeks of lactation did not affect PRL or ACTH secretion, but decreased plasma LH levels despite comparable GnRH receptor density between food-restricted and ad-libitum fed females. In the second experiments we investigated a possible causal relationship between the increased secretion of progesterone seen in food-restricted females and the suppression of plasma LH levels, by determining the effects of bromocryptine treatment and ovariectomy on LH secretion in both ad-libitum fed and food-restricted lactating females. LH suppression in food-restricted lactating females was not affected by ovariectomy or bromocryptine treatment, although the latter treatment significantly increased GnRH receptor number. These data suggest that factors other than ovarian steroids, PRL or increased adrenocortical activity modulate LH secretion and the length of lactational dioestrus in food-restricted lactating females.
Journal of Endocrinology (1995) 146, 95–104
Type II thyroxine 5′-deiodinase in the rat thymus
Authors: Molinero P , Osuna C , Guerrero J M 
Published: December 2008

Abstract
In the present study we have shown type II thyroxine 5′-deiodination (5′D) in the rat thymus. The enzyme activity was identified in crude extract homogenates by measuring the 125I released from [3′,5′-125I]thyroxine which is used as a substrate of the reaction. The release of 125I is dependent on protein tissue concentration, time, temperature and pH, and is saturable by increasing the substrate concentration, indicating its enzymatic nature. Characteristics of the enzyme activity also include a low Km (9·1 nm), its dependence on dithiothreitol, and its inhibition by iopanoic acid, but not by propylthiouracil. Experiments to investigate the cellular location of the enzyme in the thymic gland showed that the enzyme is present in both stromal cells and thymocytes. At the subcellular level, 5′D activity was associated with cellular membranes. Thyroid status appears to regulate 5′D activity in rat thymus. Hypothyroidism caused an increase in thymus 5′D activity. The Km value remained unchanged (9·1 vs 10·5 nm) during hypothyroidism, but Vmax increased significantly from 17·7 fmol/mg protein per h in euthyroid rats to 53·5 fmol/mg protein per h in hypothyroid rats. 5′D activity was also modulated by catecholamines through β-adrenergic receptors because isoproterenol, but not methoxamine or clonidine, could activate the enzyme. Because these characteristics define the type II iodothyronine-deiodinating pathway in other tissues, we suggest that the rat thymus also shares this pathway.
Journal of Endocrinology (1995) 146, 105–111
Pronounced seasonal rhythms in plasma somatolactin levels in rainbow trout
Authors: Rand-Weaver M , Pottinger T G , Sumpter J P 
Published: December 2008

Abstract
The aim of this study was to establish whether there are seasonal or age-related changes in circulating levels of somatolactin (SL) in rainbow trout (Onchorhynchus mykiss). SL levels were determined in blood sampled at monthly intervals over a 2-year period from a population of rainbow trout maintained under a natural daylength and temperature regime (North-West England, latitude 54°20′ N). SL levels displayed a distinct circannual cycle, with peak levels in summer (17–20 μg/l) and lowest levels occurring in winter (0·2–2 μg/l). This variation in SL levels was closely correlated with water temperature (P<0·001) but was out of phase with changes in daylength. Plasma SL levels were significantly higher in both mature male and female fish compared with immature fish. Plasma prolactin levels were determined to provide information on a hormone structurally related to SL, and also because mammalian prolactin is known to show distinct seasonal cycles. However, trout prolactin, in contrast to SL, did not show a pronounced seasonal pattern, although prolactin levels were significantly, but inversely, correlated with water temperature (P<0·001).
Journal of Endocrinology (1995) 146, 113–119
Differential acetylation of pro-opiomelanocortin-derived peptides in the pituitary gland of Xenopus laevis in relation to background adaptation
Authors: van Strien F J C , Galas L , Jenks B G , Roubos E W 
Published: December 2008

Abstract
Immunocytochemical analysis revealed the presence of acetylated endorphins in both melanotropes and corticotropes of the pituitary gland of Xenopus laevis. Chemical acetylation studies to determine the steady-state level of acetylated versus non-acetylated endorphins showed that virtually all endorphins are acetylated in both melanotropes and corticotropes. Apparently Xenopus is unique among vertebrates as non-acetylated endorphins are major endproducts in the distal lobe of all other vertebrate species studied thus far. The dynamics of endorphin biosynthesis in melanotrope cells using pulse-chase analysis coupled to immunoaffinity chromatography revealed that processing of pro-opiomelanocortin to produce N-terminalacetylated endorphins is very rapid. To determine the effect of long-term background adaptation on acetylation status of endorphins and α-MSH-related peptides, Xenopus laevis were adapted for 3 or 6 weeks to either a black or a white background. In both physiological states the major intracellular form of α-MSH-related peptides in melanotropes was desacetyl α-MSH while the major endorphin-related peptide was α,N-acetyl-β-endorphin[1–8]. In the medium of superfused neurointermediate lobes of black background-adapted animals the major form of secreted melanotropins and endorphins was α-MSH and α,N-acetyl-β-endorphin[1–8] respectively. We conclude that there is a marked spatio-temporal difference in acetylation of melanotropin and endorphins, with rapid intracellular acetylation of endorphins while melanotropin is acetylated at the time of its exocytosis. In the medium of superfused neurointermediate lobes of white background-adapted animals the amount of desacetyl α-MSH was much higher than in the medium of lobes of black-adapted animals. Therefore, the secretory signals from melanotrope cells of black- and white-adapted Xenopus appear to differ with respect to the degree of acetylation of the melanotropins. This difference may underlie the strategy of Xenopus to regulate dermal melanophore activity during physiological background adaptations.
Journal of Endocrinology (1995) 146, 159–167
Uptake of thyroxine in the human choriocarcinoma cell line JAR
Authors: Mitchell A M , Manley S W , Payne E J , Mortimer R H 
Published: December 2008

Abstract
We have studied the uptake of 125I-thyroxine (125I-T4) in the human choriocarcinoma cell line JAR. Uptake of 125I-T4 was time-dependent, stereospecific and reversible, with a saturable component of 33% after 120 min of incubation. Kinetic analysis of the initial specific uptake rates indicated the presence of a single uptake process with a Michaelis constant of 59·4 ± 13·9 nm (n=12) and maximum velocity of 0·29 ± 0·06 pmol/min per mg protein. Uptake was dependent on intracellular energy as, in the presence of 2 mm potassium cyanide, saturable uptake was reduced to 60·6 ± 8·5% (n=4) of control uptake. Uptake was also temperature-dependent. Saturable 125I-T4 uptake after 60 min of incubation was 26·1 ± 3·0% at 25 °C (n=6) and 27·3 ± 5·7% at 4 °C of control uptake at 37 °C. Ouabain did not inhibit 125I-T4 uptake indicating that the uptake was independent of the Na gradient across the cell membrane. Although T4 uptake was stereospecific, as d-T4 failed to inhibit 125I-l-T4 uptake, it was not specific for T4, as tri-iodothyronine (T3) and reverse T3 also inhibited 125I-T4 uptake. We conclude that JAR cells have a saturable, stereospecific and reversible membrane transport mechanism for T4 which is dependent on intracellular energy, but independent of the Na+ gradient across the cell membrane.
Journal of Endocrinology (1995) 146, 233–238
The in vivo effects of fibroblast growth factor and epidermal growth factor on the secretion of oestradiol, androstenedione and progesterone by the autotransplanted ovary in the ewe
Authors: Scaramuzzi R J , Downing J A 
Published: December 2008

Abstract
An experiment was conducted to determine the effects of epidermal growth factor (EGF) and fibroblast growth factor (FGF), infused into the ovarian artery, on the secretion of ovarian steroids during the mid-luteal phase in ewes with an autotransplanted ovary. The infusion of EGF (5 μg/h) for 12 h suppressed the secretion of oestradiol and androstenedione during the infusion and for up to 30 h after the infusion. The secretion of progesterone tended to be lower immediately after the infusion (not significant) but had recovered by 24 h after the end of the infusion and then increased significantly (P<0·05) to rates higher than in control animals. There were no effects of the infusion of EGF on the characteristics of pulsatile LH secretion. FSH concentrations increased 24 h after the end of the infusion probably as an indirect consequence of the changes in oestradiol secretion and not as a consequence of a direct effect of EGF on the hypothalamo-pituitary axis although this latter possibility cannot be unequivocally eliminated. The infusion of FGF (1·5 μg/h) for 12 h also suppressed the secretion of oestradiol and androstenedione during and for up to 30 h after the infusion. The infusion of FGF had no detectable effect on the secretion of progesterone or the characteristics of pulsatile LH secretion. FSH concentrations increased steadily during the infusion but declined rapidly to below pre-infusion concentrations after the end of the infusion. These data provide tentative in vivo evidence for paracrine and autocrine effects of EGF and FGF on follicular and luteal function in sheep.
Journal of Endocrinology (1995) 146, 301–311
Functional and morphological changes of the thyroid gland following 5 days of pulsatile TRH stimulation in male rats
Authors: Hoang-Vu C , Brabant G , Leitolf H , von zur Mühlen A , Dralle H , Schröder S , Sierralta W D 
Published: December 2008

Abstract
The aim of the present study was to evaluate in vivo the selective effects of a small increase in plasma TSH levels on thyroid function, proliferation and morphology. Chronically catheterized male Sprague–Dawley rats were stimulated i.v. over 5 days either with TRH (2 μg TRH in 100 μl 0·9% (w/v) NaCl (TRH-P) or the NaCl carrier alone (P), both given as pulses every 2 h. Control groups were cotreated i.v. with 10 μg thyroxine (T4)/100 g body weight per day (TRH-P+T4) starting 2 days before pulsatile stimulation. TSH plasma levels were approximately doubled by TRH-P (P≤0·001), T4 plasma levels significantly increased (P≤0·001) but tri-iodothyronine plasma levels did not change compared with treatment with P. No significant changes between groups were found in thyroid weight and in intrathyroidal iodine content, but the percentage of 5-bromo-2′-desoxyuridinelabelled thyrocytes as a marker of proliferation in TRH-P-treated animals was significantly increased over P or TRH-P+T4 (P≤0·001). Ultrastructural analysis of the thyroid evaluated by electron microscopy revealed a significant increase in the number of lysosomes (P≤0·001). The size of the endoplasmic reticulum (ER) in relation to the cytoplasm was significantly increased when treated with TRH-P compared with P or TRH-P+T4 (P≤0·001). Post-embedding immunogold staining revealed Tg as a major product within ER cisternae. Immunogold labelling was moderate in controls and higher densities of gold particles were obtained in TRH-P-treated animals (P≤0·001). In conclusion, short-term pulsatile TRH stimulation increasing the plasma levels of immunoreactive TSH only twofold is capable of inducing hypertrophy of the thyrocytes by gross ultrastructural changes which are paralleled by an increase in circulating T4. These data underscore the dominant role of TSH on thyroid ultrastructure within the narrow boundaries of normal physiological regulation.
Journal of Endocrinology (1995) 146, 339–348
Influence of treatment with the anti-oestrogen 3-hydroxytamoxifen (droloxifene) on plasma sex hormone levels in postmenopausal patients with breast cancer
Authors: Geisler J , Haarstad H , Gundersen S , Raabe N , Kvinnsland S , Lønning P E 
Published: December 2008

Abstract
Plasma levels of oestradiol (Oe2), oestrone (Oe1), oestrone sulphate (Oe1S), androstenedione, testosterone, dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulphate (DHEAS), sex hormone-binding globulin (SHBG) and the gonadotrophins (FSH and LH) were determined in 20 postmenopausal women with breast cancer treated with the anti-oestrogen droloxifene (3-hydroxytamoxifen). Plasma oestrogens were measured before and after 3, 6 and 12 months of therapy. The other hormones were measured before and after 6 months of therapy. Droloxifene treatment had no significant influence on plasma levels of Oe2. Plasma levels of Oe1 and Oe1S increased during treatment (mean increase of 11·9-15·9% and 24·5–69·4% respectively after different time-intervals on treatment). The Oe1S/Oe1 and Oe1S/Oe2 ratios increased by mean values of 13·8–45·2% and 25·9–52·4% respectively. Plasma SHBG increased significantly by a mean value of 73·9%, while FSH and LH fell non-significantly by 19·7% and 20·4% respectively. Plasma levels of testosterone, androstenedione, DHEA and DHEAS all increased during treatment, but none of these alterations were of statistical significance. While the influence of droloxifene on plasma SHBG resembled that which is seen during treatment with tamoxifen, its influence on plasma oestrogens and the gonadotrophins seems to be different. Possible explanations of such differences and the clinical implications of alterations in plasma hormones during treatment with droloxifene are discussed.
Journal of Endocrinology (1995) 146, 359–363
Corticotrophin-releasing hormone-binding protein in human fetal plasma
Authors: Perkins A V , Wolfe C D A , Eben F , Soothill P , Linton E A 
Published: December 2008

Abstract
During pregnancy maternal plasma corticotrophinreleasing hormone (CRH) levels rise 1000-fold whilst fetal plasma levels are often 100-fold higher than the concentrations seen in normal non-pregnant human plasma. Despite these high CRH levels neither the maternal nor fetal pituitary releases excessive amounts of ACTH. A specific CRH-binding protein (CRHBP) exists in the maternal circulation which is able to bind and inactivate the ACTH releasing activity of CRH. In this study we have used a specific CRHBP radioimmunoassay to determine the level of CRHBP in fetal and maternal plasma samples. Fetal samples were collected by cordocentesis between 20 and 33 weeks gestation and matched maternal samples were taken by venepuncture at the same time. In a second study, plasma samples were collected from 8 women at fortnightly intervals from week 20 to term, at labour and post-partum. A fetal sample, taken from the umbilical vein, was collected immediately post-delivery. The mean maternal CRHBP concentration for the samples collected between 20 and 33 weeks (n=23) was 8·12 nmol/l and the fetal level was 8·62 nmol/l. Data from the second study showed that at term the maternal CRHBP concentration decreased significantly (P<0·025) to 6·32 nmol/l. The fetal CRHBP level also decreased significantly (P<0·001) at term to a level of 5·84 nmol/l. The CRHBP in both fetal and maternal plasma was shown to be functional by 125I-CRH binding and gel permeation chromatography. The capacity of maternal and fetal plasma to bind 125I-CRH decreased at term in agreement with the quantitation of plasma CRHBP by radioimmunoassay.
Journal of Endocrinology (1995) 146, 395–401
Activin inhibits but inhibin activates mouse placental lactogen-II secretion
Authors: Yamaguchi M , Tasaka K , Ogura K , Sakata M , Mizuki J , Miyake A 
Published: December 2008

Abstract
The regulation of mouse placental lactogen (mPL)-I and mPL-II secretion by activin and inhibin and the expression of activin and inhibin subunit mRNAs in the mouse decidua were examined. Activin-A at a concentration of 10 nm/l significantly inhibited mPL-II secretion by placental cells from days 9 and 12 of pregnancy. However, activin-A did not affect mPL-I secretion by cells from days 7 and 9 of pregnancy nor mPL-II secretion by cells from day 7 of pregnancy. By contrast, 10 nm/l inhibin activated mPL-II secretion by cells from day 12 of pregnancy. These effects of activin and inhibin on mPL-II secretion were dose-dependent. Follistatin, which binds to activin and blocks its bioactivity, completely eliminated the inhibitory effect of activin on mPL-II secretion. Incubation of placental cells from day 12 of pregnancy with activin-A resulted in a significant reduction of the mPL-II mRNA level assessed by Northern blot analysis. Northern blot analysis using poly(A)+ RNA extracted from the decidua indicated that mouse decidua, as well as the placenta, express all activin and inhibin subunits and that their gene expressions increased during gestation. The expression of these mRNAs in the decidua was much higher than those in the placenta. These findings suggest that activin and inhibin regulate mPL-II secretion and suggest the presence of an autocrine or paracrine regulation of mPL-II secretion in mouse placenta by activin and inhibin after mid-pregnancy in vivo.
Journal of Endocrinology (1995) 146, 469–474
GH-deficient dw/dw rats and lit/lit mice show increased Fos expression in the hypothalamic arcuate nucleus following systemic injection of GH-releasing peptide-6
Authors: Dickson S L , Doutrelant-Viltart O , Leng G 
Published: December 2008

Abstract
In the rat, the synthetic GH secretagogue GH-releasing peptide (GHRP-6) acts centrally to activate a subpopulation of arcuate neurones as reflected by increased electrical activation and by the detection of Fos protein in cell nuclei. Since GHRP-6 also induces GH secretion via a direct action on the pituitary, we set out to determine whether the central actions of GHRP-6 are mediated by GH itself. First, we demonstrated that peripherally administered GHRP-6 induces Fos expression in the arcuate nucleus of GH-deficient animals (dw/dw rats and lit/lit mice). Secondly, in dw/dw rats, neither intracerebro-ventricular injection of 15 μg recombinant bovine GH nor 1 μg recombinant human IGF-I resulted in an increase in the number of cells expressing Fos protein in the arcuate nucleus (or in any other hypothalamic structure studied). These results support our hypothesis that GHRP-6 has a central site and mechanism of action and provide evidence to suggest that the activation of arcuate neurones by GHRP-6 is not mediated by a central action of GH or IGF-I. Furthermore, since the lit/lit mouse pituitary does not release GH following GHRP-6 administration, our finding that the central actions of GHRP-6 remain intact in these animals suggests the possible existence of two subpopulations of putative GHRP-6 receptors.
Journal of Endocrinology (1995) 146, 519–526
Effects of melatonin in the mediobasal hypothalamus on the secretion of gonadotrophins in sheep: role of dopaminergic pathways
Authors: Tortonese D J , Lincoln G A 
Published: December 2008

Abstract
Previous studies have shown that treatment with microimplants of melatonin in the mediobasal hypothalamus (MBH) of sexually inactive Soay rams exposed to long days induces an increase in the secretion of FSH and reactivation of the testicular axis, as normally occurs in response to short days. The current study was conducted to investigate the possible involvement of hypothalamic dopaminergic (DA) systems in this melatonin-induced effect. At 10 weeks under long days, sexually inactive Soay rams were treated in the MBH with micro-implants containing bromocriptine (DA agonist) or sulpiride (DA antagonist), given alone or in combination with melatonin, to establish whether the DA drugs would mimic or negate the effects of melatonin. All micro-implants were inserted bilaterally and left in place for 14 weeks; the study lasted a total of 28 weeks (14 weeks implant period and 14 weeks post-implant period) while the animals remained under long days. The ability of the micro-implants to release bromocriptine and sulpiride for 14 weeks was confirmed by incubating implants in vitro and testing for the presence of the compounds in the incubate using a pituitary cell bioassay. Profiles of FSH, determined in blood samples collected three times weekly, were significantly different among treatments (time × treatment interaction, P<0·001, ANOVA). Melatonin in the MBH induced a marked increase in the concentrations of FSH during the implant period, and a decrease during the post-implant period (P<0·001). Bromocriptine given alone in the MBH induced a decrease in the concentrations of FSH which became statistically different from the control during the post-implant period (P<0·05). Treatment with sulpiride alone also resulted in a suppressive effect during the post-implant period (P<0·01). When given in combination with melatonin, bromocriptine or sulpiride significantly reduced the melatonin-induced increase in the concentrations of FSH observed during the implant period (P<0·001). The results support the view that DA pathways in the MBH play an important role in the inhibitory regulation of gonadotrophin secretion in the ram. The inhibitory effect of bromocriptine is likely to result from the direct activation of the hypothalamic DA receptors linked to GnRH neurones regulating the secretion of FSH. The apparent paradoxical inhibitory effect of sulpiride is thought to be due to enhanced gonadal steroid negative feedback resulting from blockade of the inhibitory DA pathways, as evidenced by significantly increased secretion of testosterone (P<0·05) in the animals receiving sulpiride in combination with melatonin. The observation that DA drugs modified the effects of melatonin in the MBH provides evidence that hypothalamic DA pathways may participate in the mechanism by which melatonin mediates the effects of photoperiod on reproductive function in the ram.
Journal of Endocrinology (1995) 146, 543–552