bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential modulation by Ca2+ of iodide transport processes in a cultured rat thyroid cell strain
Authors: Bidey S. P. , Tomlinson S. 
Published: December 2008

ABSTRACT
The interrelationship between the roles of Ca2+ and cyclic AMP (cAMP) in the control of intracellular iodide accumulation was investigated in the continuous rat thyroid cell strain FRTL-5. Using incubation conditions designed to allow independent study of iodide uptake and efflux into the incubation medium, dibutyryl cAMP (dbcAMP) mimicked the effect of TSH in enhancing iodide uptake, but the responses to both stimulators were decreased in the presence of the Ca2+ ionophore A23187, although the ionophore was ineffective when addition was delayed until after withdrawal of the stimulators. l-Adrenaline, an α-adrenergic agonist inactive with respect to cAMP accumulation in this cell strain, was also inactive with regard to iodide uptake. The rapid efflux of iodide from FRTL-5 cells seen in response to TSH was not mimicked by dbcAMP, but was reproduced by A23187, providing evidence for the involvement of Ca2+ in the release process. Under the latter conditions, no additional effect of TSH was obtained. l-Adrenaline also stimulated iodide efflux, in support of a possible role of α-adrenergic agonists in controlling the apical membrane presentation of iodide in vivo.
The observed differential effects of dbcAMP and α-adrenergic agonists on iodide uptake and efflux respectively, provide further evidence for the existence of two functionally distinct mechanisms controlling the available level of intracellular iodide. Opposing effects of free intracellular Ca2+ may, however, serve to control the activities of both influx and efflux processes since, whilst experimental increments in Ca2+ appear to promote iodide efflux through a non-cAMP-mediated pathway, inhibition by intracellular Ca2+ of thyroid cell cAMP accumulation may explain both the decreased response of iodide uptake observed in the presence of A23187, and the reduced stimulation effected by TSH under such conditions.
J. Endocr. (1987) 112, 51–56
Somatostatin partially reverses desensitization of somatotrophs induced by growth hormone-releasing factor
Authors: Clayton R. N. , Bailey L. C. 
Published: December 2008

ABSTRACT
The effect of somatostatin on GH-releasing factor (GRF)-induced desensitization of somatotrophs was studied in vitro. Primary cultures of rat anterior pituitary cells pretreated for 4 or 18 h with GRF(1–40) (100 nmol/l) showed a 50% or greater reduction in maximal GH release when rechallenged with 10 nmol GRF/l. Rechallenge GRF dose–response curves were either very flat, making accurate measurement of the dose giving 50% maximum stimulation (ED50) impossible, or the ED50 concentration was increased from 0·3 nmol/l (untreated) to 2 nmol/l (GRF pretreated). Although GRF pretreatment reduced cellular GH content by 40–50%, correction for this did not restore GRF responsiveness measured in terms of maximal GRF-stimulated/unstimulated GH release (maximal/basal ratio), or the GRF ED50 concentration. Maximal/basal GH release per 4 h from GRF-pretreated cells was reduced when cells were rechallenged with forskolin (5 μmol/l) or calcium ionophore (A23187; 10 μmol/l), to the same extent as when rechallenged with 10 nmol GRF/l. Although this might be explained by a reduction in the pool of releasable GH, an alternative explanation is that pretreatment with GRF disrupts the GH release mechanism(s) at a common step(s) beyond cyclic AMP generation and Ca2+ influx.
Co-incubation of cells with somatostatin and GRF (100 nmol/l) partially reversed the desensitizing action of GRF during both 4- and 18-h pretreatments in a dose-dependent manner, with 1 μmol somatostatin/l being most effective. Maximal GRF (100 nmol/l)-stimulated/basal GH release was 4·4 ± 1·0 (mean ± s.e.m., n = four experiments), 1·55 ± 0·09 and 2·43 ± 0·1 for control, GRF-pretreated (4 h) and GRF plus somatostatin-pretreated cells respectively. Comparable values for cells pretreated for 18 h were 3·66 ± 0·44 (n = three experiments), 1·78 ± 0·28 and 3·04 ± 0·04 for control, GRF- and GRF plus somatostatin-pretreated cells. Somatostatin reduced the 50% depletion of cellular GH caused by GRF pretreatment to 15–20%, as well as attenuating GH released during the pretreatment period by 40 ± 5% (mean ± s.e.m., n = seven experiments). Somatostatin restored somatotroph sensitivity of GRF-desensitized cells indicating that, in addition to reversing depletion of the releasable pool of GH, the counter-regulatory hormone also prevents disruption of post-receptor cellular biochemical events which remain to be identified. These results add to the list of GRF actions inhibited by somatostatin and suggest a potentially important role for somatostatin in vivo to maintain somatotroph responsiveness to GRF.
J. Endocr. (1987) 112, 69–76
Changes in protein metabolism of ovine primary muscle cultures on treatment with growth hormone, insulin, insulin-like growth factor I or epidermal growth factor
Authors: Harper J. M. M. , Soar J. B. , Buttery P. J. 
Published: December 2008

ABSTRACT
Methods for the primary culture of muscle cells from fetal sheep were developed which gave high yields of cells. Myoblasts were grown in vitro, and allowed to fuse to form contractile multinucleate myotubes; these could be maintained in a good condition for at least 2 weeks. Protein turnover in these differentiated cultures was examined for sensitivity to each of four potentially anabolic peptide hormones and growth factors: insulin, insulin-like growth factor I (somatomedin C), epidermal growth factor and growth hormone. Insulin was found to have no effect except at high concentrations (1 μmol/l), compatible with its role as a somatomedin analogue. Insulin-like growth factor I was active at lower levels (1 nmol/l) but the cultures were not as responsive to it as were primary rat muscle cultures or differentiated L6 cells, which were tested in similar experiments. The maximum stimulation of protein synthesis observed with the ruminant system was only 16%. Epidermal growth factor was highly anabolic for primary cultures from sheep muscle, and the cells were very sensitive to it, half-maximal stimulation of protein synthesis being seen with concentrations as low as 20 pmol/l. No effects of bovine growth hormone were seen in the ovine system. However, an inhibition of protein breakdown was found with high concentrations (0·1 μmol/l) in the L6 rat myoblast cell line. It was found that the culture conditions used could affect the observed responses of protein synthesis and degradation, despite withdrawal of serum from the incubation media 22 h before testing.
J. Endocr. (1987) 112, 87–96
Synergistic stimulation of Swiss mouse 3T3 fibroblasts by epidermal growth factor and other factors in human mammary secretions
Authors: Corps A. N. , Blakeley D. M. , Carr J. , Rees L. H. , Brown K. D. 
Published: December 2008

ABSTRACT
The concentration of epidermal growth factor (EGF) in human mammary secretions was about 50 nmol/l for several weeks prepartum. It then fell to about 13 nmol/l within 4 days after parturition, in parallel with the decrease in protein concentration which is associated with the onset of lactation. In contrast, the concentration of EGF in urine samples from the same donors remained constant throughout this period. All the immunoreactive EGF in mammary secretions competed at the EGF receptors on Swiss mouse 3T3 fibroblasts. The stimulation of these cells by samples of mammary secretions was, however, much greater than that induced by EGF alone, indicating the presence of other factors which synergize with EGF. Gel filtration of mammary secretions revealed two major peaks of mitogenic activity, corresponding to EGF and a factor of higher molecular weight. The latter could synergize with added EGF, insulin or bombesin, and thus falls into a different functional class from any of these factors.
J. Endocr. (1987) 112, 151–159
Ornithine decarboxylase activity in small ovarian follicles from the laying hen (Gallus domesticus): a comparison of follicles from several regions of the ovary
Authors: Armstrong D. G. 
Published: December 2008

ABSTRACT
Small non-atretic follicles (1·5–250 mg) were collected from four distinct areas of the ovary of the laying hen. These were as follows: (1) the stalks of the two largest preovulatory follicles; (2) the stalks of the third largest preovulatory follicle; (3) the stalks of the fourth and fifth largest preovulatory follicle and (4) zona parenchymatosa.
There was an increase in the proportion of small follicles in the size range 1·5–10 mg collected from the stalks of the large yellow yolky preovulatory follicles approaching ovulation, with a corresponding decrease in the number of small follicles in the size group 10–250 mg. In addition, the ornithine decarboxylase activity in follicles collected from regions 1 and 2 was significantly greater than that in small follicles collected from region 4.
Since the level of ornithine decarboxylase activity is critically dependent on the degree of hormonal stimulation and growth rate of the tissue, it is suggested, on the basis of the differences in their ornithine decarboxylase activity, that small follicles located on the stalks of the large yolky preovulatory follicles are stimulated by trophic hormones and growth factors to a greater degree than similarly sized follicles located elsewhere in the ovary. It is proposed that this increased stimulation may increase the chances of these small follicles being recruited into the hierarchy.
J. Endocr. (1987) 112, 183–187
Regeneration of the thymus in old male rats treated with a stable analogue of LHRH
Authors: Greenstein B. D. , Fitzpatrick F. T. A. , Kendall M. D. , Wheeler M. J. 
Published: December 2008

ABSTRACT
It has been shown that the thymus can be regenerated in intact old rats by implanting s.c. a stable analogue of LHRH. Old male rats were given s.c. implants of osmotic pumps containing a solution in citrate buffer of the analogue which was given at a rate of 1 μg/h for 28 days. Some animals were given pumps containing buffer alone, and another group of rats was orchidectomized. The animals were killed after 28 days and the tissues weighed and taken for histology. Serum testosterone was measured by radioimmunoassay.
Sham-treated rats had small fatty thymuses, which were poorly organized with a very narrow band of cortex. Animals treated with the analogue of LHRH and those which had been orchidectomized had relatively large thymuses which were multi-lobed in drug-treated rats, and atrophied accessory sex organs. The testes were grossly atrophied in analogue-treated rats. Histologically, the thymus looked healthy, having a wide, thymocyte-filled cortex and a clearly defined corticomedullary junction. Serum testosterone concentrations were similar in orchidectomized and analogue-treated rats.
It is concluded that it is possible to regenerate the thymus in old rats treated with an analogue of LHRH, but the effect is accompanied by chemical castration. It is also clear that the old pituitary gland is susceptible to the desensitizing action of an LHRH analogue.
J. Endocr. (1987) 112, 345–350
Levels of LH-releasing hormone in hypophysial stalk plasma during an oestrogen-stimulated surge of LH in ovariectomized rats
Authors: de Greef W. J. , de Koning J. , Tijssen A. M. I. , Karels B. 
Published: December 2008

ABSTRACT
Treatment of ovariectomized rats with 50 μg oestradiol benzoate, followed by 20 μg oestradiol benzoate 3 days later, induced surges of LH and FSH on the day following the second injection with oestradiol benzoate. During this surge of gonadotrophins, which was not blocked by the anaesthetic required to collect hypophysial stalk blood, increased hypophysial stalk plasma levels of immunoreactive LHRH were noted. Furthermore, the levels of LHRH in hypophysial portal blood were found to fluctuate. Measurement of LHRH in a pool of portal plasma revealed similar results when determined by radioimmunoassay and by a sensitive in-vitro bioassay.
To mimic the observed release of LHRH during the surge of gonadotrophins, LHRH was infused, either systemically or directly into a long portal vessel, into oestrogen-treated, ovariectomized rats which had their endogenous release of LHRH blocked by pentobarbitone. An infusion of LHRH into the jugular vein, resulting in peripheral levels of LHRH which were somewhat lower than those measured in hypophysial stalk plasma, caused a surge of FSH similar to that found in rats used for collection of hypophysial stalk blood. When compared with the values in the latter animals, however, the levels of LH became two to four times higher by this infusion of LHRH. When LHRH was infused directly into a long portal vessel to mimic the observed secretion rate of LHRH during the oestrogen-stimulated surge of gonadotrophins, then the surges of LH and FSH were lower than those observed in the rats used for collection of stalk blood.
J. Endocr. (1987) 112, 351–359
Ionic mechanisms regulating thyroidal secretion: effects of ouabain and medium sodium concentration on radioiodine release from cultured porcine thyroid cells
Authors: Manley S. W. , Bourke J. R. , Huxham G. J. 
Published: December 2008

ABSTRACT
Thyrotrophin stimulated release of radioiodine from the organic iodine pool of cultured porcine thyroid cells. The response was well developed within 2–4 h of incubation. Inhibition of the Na+/K+ pump with ouabain or incubation in sodium-free medium inhibited the response to TSH. The magnesium content of cultures was reduced by ouabain, and increasing the magnesium concentration of the medium to 10 mmol/l reversed the inhibition of the TSH response by ouabain. After prolonged incubation (4–6 h), ouabain in magnesium-enriched medium stimulated release of radioiodine. Its effects were not additive with those of TSH. Incubation for 4–6 h in media of reduced sodium concentration (34 mmol/l) also stimulated release. Sodium-free medium alone did not alter basal release rates, but magnesium enrichment of sodium-free medium promoted release after 4 h of incubation. It was concluded that the previously reported inhibition of the TSH response in thyroid tissue by ouabain or sodium-free medium was due to secondary derangements of cellular function rather than to a specific blockade of the secretomotor signal. The data are consistent with the hypothesis that a reduction in the sodium ion electrochemical gradient across the cell membrane mediates the secretomotor effect of TSH.
J. Endocr. (1987) 112, 399–405
Adrenal status during the first month of life in mature and premature human infants
Authors: Wallace A. M. , Beesley J. , Thomson M. , Giles C. A. , Ross A. M. , Taylor N. F. 
Published: December 2008

ABSTRACT
Measurements of (a) 17-hydroxyprogesterone (17-OHP) in blood collected onto filter paper after heel puncture by lancet and (b) steroid metabolites in random collections of urine, were made in human infants born from 25 weeks of gestation onwards. The concentration of 17-OHP in blood eluted from filter paper samples was inversely related to both gestational age and birth weight. In mature infants, 17-OHP concentrations fell rapidly soon after birth, whereas concentrations remained high over the first month of life in infants born earlier than 33 weeks of gestation. Sulphated urinary steroids were identified as having a 3β-hydroxy-5-ene structure and although the pattern of excretion was similar in mature and premature infants, significantly higher concentrations were found in the premature group. Steroid metabolites normally present when concentrations of circulating 17-OHP are increased due to 21-hydroxylase deficiency were not detectable in urine samples collected from infants born prematurely. Where direct comparison of 17-OHP in blood spots and urinary steroid metabolites was possible, the concentrations of 17-OHP in blood samples paralleled 3β-hydroxy-5-ene steroid metabolites in urine. The results suggest that a circulating cross-reacting 3β-hydroxy-5-ene steroid may be responsible for increased concentrations of 17-OHP in infants born prematurely. Increased concentrations of both 17-OHP in blood spots and steroid sulphates in urine were associated with stress in premature, but not in more mature, infants suggesting that in infants born prematurely postnatal stress may delay adrenal maturation.
J. Endocr. (1987) 112, 473–480
STEROIDAL PURE ANTIOESTROGENS
Authors: Wakeling A.E. , Bowler J. 
Published: December 2008

ABSTRACT
The effects of some novel 7α-alkyl amide analogues of oestradiol on the rat and mouse uterus have been measured. The compound ICI 164,384 [N-n-butyl-N-methyl-11-(3,17β-dihydroxyoestra-1,3,5(10)-trien-7αyl) undecamide] was entirely devoid of oestrogenic activity in the rat and mouse uterus but completely blocked the uterine stimulatory effects of oestradiol and of tamoxifen. Biological activity was confined to 7α-isomers. The affinity of ICI 164,384 for the rat uterus oestrogen receptor (0.19) was substantially greater than that of tamoxifen (0.025 c.f. oestradiol=l). The compound inhibited oestradiol-induced growth of ZR-71-1 cells in a dose-dependent manner in vitro. ICI 164,384 thus has the characteristics of a pure antagonist of oestrogen action.
Failure of the synthetic androgen 17β-hydroxy-17α-methylestra-4,9,11-triene-3-one (methyltrienolone, R1881) to duplicate the activational effect of testosterone on mating in castrated male rats
Authors: Baum M. J. , Kingsbury P. A. , Erskine M. S. 
Published: December 2008

ABSTRACT
Administration of the synthetic steroid, 17β-hydroxy-17α-methyl-estra-4,9,11-triene-3-one (methyltrienolone, R1881), which is an androgen receptor agonist not metabolized in vivo, at doses of 400, 800 or 2400 μg/kg s.c. in propylene glycol stimulated mounting and ejaculation only slightly in sexually experienced castrated rats. A similar low level of mating was observed in a group of castrated rats given testosterone at doses of 400 followed by 800 μg/kg. However, when treated with a higher dose of testosterone (2400 μg/kg) these castrated rats displayed significantly higher levels of mounting and ejaculation than rats treated with any of the doses of R1881. Also, when this higher dosage of testosterone was substituted for each dose of R1881, significant increments in mounting and ejaculation occurred in all groups. These findings show that R1881 is only marginally effective in restoring sexual behaviour in castrated rats, suggesting that the activation of neural androgen receptors cannot by itself account for the activational effect of testosterone on mating behaviour in gonadally intact male rats.
J. Endocr. (1987) 113,15–20
Effects of catecholaminergic blockade by haloperidol or propranolol at different stages of the oestrous cycle on ovulation and gonadotrophin levels in the rat
Authors: Domínguez R. , Gaitán C. M. , Méndez S. A. , Ulloa-Aguirre A. 
Published: December 2008

ABSTRACT
Rats with a 4-day oestrous cycle were injected with 2·5 mg haloperidol/kg, a dopaminergic blocker, or with 2·0 mg propranolol/kg, a β1- and β2-receptor blocker, at 13.00 h on oestrus, dioestrous day 1, diestrous day 2 or pro-oestrus. Animals were autopsied on the next expected day of oestrus. Haloperidol blocked ovulation when injected on oestrus, dioestrous day 1 or pro-oestrus and was less effective when injected on dioestrous day 2. Propranolol caused a decrease in the number of ova shed when injected on dioestrous day 2 or pro-oestrus. Serum concentrations of FSH at oestrus were below the control values in those animals in which ovulation was blocked by haloperidol. No significant changes in serum concentrations of LH were observed. The normal gonadotrophin peak which occurs during the afternoon of pro-oestrus was blocked by administration of haloperidol on oestrus or dioestrous day 1. Administration of gonadotrophin-releasing hormone (GnRH) to haloperidol-treated animals on oestrus or dioestrous day 1 did not restore ovulation or increase serum FSH levels. When the same dose of GnRH was given to rats treated with haloperidol on pro-oestrus, they all ovulated and their FSH levels rose normally. Treatment with both FSH and LH of rats given haloperidol at oestrus restored ovulation in 50% of the animals, whereas it was ineffective in animals treated on dioestrous day 1. Fifty per cent of the animals treated with haloperidol on oestrus or dioestrous day 1 ovulated when oestradiol benzoate was injected on dioestrous day 2.
These results suggest that the dopaminergic and adrenergic systems have different roles in the regulation of the oestrous cycle and ovulation. The decrease in the number of ova shed induced by propranolol may be related to the blockade of receptors at the level of the ovary. The sensitivity of the dopaminergic systems involved in gonadotrophin control seems to vary depending on the day of the oestrous cycle. It is possible that when the dopaminergic system is blocked at the beginning of the cycle, an alteration in oestrogen secretion might be produced, initiating a chain of events at the hypothalamic-pituitary-ovarian axis which will ultimately inhibit ovulation. Since dopaminergic blockade induces an increase in prolactin secretion, and prolactin enhances dopamine turnover at the median eminence and blocks oestrogen secretion at the level of the ovary, the present results might also reflect the effects of haloperidol at two different levels, i.e. increased dopamine turnover at the median eminence and decreased secretion of oestrogens.
J. Endocr. (1987) 113, 37–44
Somatostatin-like immunoreactivity in duck plasma, hypothalamus and neural lobe during post-hatch growth: comparison with plasma and pituitary growth hormone concentrations
Authors: Foltzer Ch. , Harvey S. , Mialhe P. 
Published: December 2008

ABSTRACT
Variations in the concentrations of plasma and pituitary GH were determined in ducks for 66 and 87 days after hatch, and compared with somatostatin-like immunoreactivity (SLI) in the plasma, hypothalamus and neural lobe. Plasma GH levels gradually decreased during growth, while pituitary GH content increased. The concentration of pituitary GH increased during the first 3 weeks of age and remained relatively constant thereafter. The decline in plasma GH concentration was paralleled by a similar fall in the level of plasma SLI. While the content of hypothalamic SLI increased during development, the SLI concentration was maximal at 14 days of age and lowest in adults. The content and concentration of SLI in the neural lobe, in contrast, increased progressively during development. Gel filtration of hypothalamic and neural lobe extracts demonstrated that both young and older birds had two main peaks of SLI, corresponding to somatostatin-14 and somatostatin-28, and a third, larger form. The elution pattern of plasma SLI was similar in young and older birds and was principally composed of a large molecular species ('big' somatostatin), although an additional small peak eluting between somatostatin-28 and somatostatin-14 was eluted from a large pool of plasma from 90-day-old ducks. These results suggest that increased plasma GH levels in young birds do not result from a hypothalamic somatostatin deficiency nor from variations in molecular forms of SLI, and that the age-related decline in plasma GH concentration is not due to a deficiency in pituitary GH content. The decline in the circulating GH level during growth is probably due to an increase in hypothalamic somatostatin release.
J. Endocr. (1987) 113, 57–63