bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blockage of K+ channels reverses the inhibitory action of atriopeptin on secretagogue-stimulated ACTH release by perifused isolated rat anterior pituitary cells
Authors: Antoni F. A. , Dayanithi G. 
Published: December 2008

ABSTRACT
The aim of the present study was to investigate how atriopeptin inhibits secretagogue-stimulated ACTH secretion in vitro. Perifused isolated rat anterior pituitary cells were used throughout; the ACTH content of the perifusate was measured by radioimmunoassy.
In the presence of a constant (0·05 nmol/l) concentration of 41-residue corticotrophin-releasing factor (CRF), arginine vasopressin (AVP; 0·05–50 nmol/l) stimulated ACTH secretion in a concentration-dependent manner, the combination of 0·05 nmol CRF/l and 0·5 nmol AVP/l (CRF/AVP) stimulated ACTH release to six- to eightfold above baseline. The effect of CRF/AVP was not modified by tetrodotoxin, but was abolished by CoCl2 and reduced to about 70% of the control stimulus by nifedipine.
Application of 103–126 residue atriopeptin for 10 min before and 2·5 min during the CRF/AVP stimulus strongly suppressed the evoked release of ACTH, the maximal inhibition was 75–90% at 10 nmol atriopeptin/l. The calcium ionophore ionomycin (200 nmol/l) reversed the effect of atriopeptin while it had no secretagogue activity of its own, and did not enhance the response to CRF/AVP. A variety of blockers of K+ channels, 4-amino pyridine, tetraethylammonium, apamine, quinine, but not tolbutamide, effectively antagonized the inhibitory action of atriopeptin (10 nmol/l). None of these drugs altered ACTH release evoked by CRF/AVP. In concentration–response experiments, the half effective concentration of 4-aminopyridine and tetraethyl-ammonium were around 1 mmol/l and 10 nmol/l for apamine. Finally, tetraethylammonium and apamine also antagonized the inhibition of CRF/AVP-evoked ACTH release by 8-Br-cGMP.
These data suggest that (1) at least two types of K+ channels, a delayed rectifier and the apamine-sensitive Ca2+-activated channel, are functionally important in pituitary corticotroph cells; (2) atriopeptin inhibits CRF/AVP-stimulated ACTH secretion by hyperpolarizing the plasma membrane and thus reducing the uptake of Ca2+ into the cells; (3) cGMP is the intracellular mediator of the action of atriopeptin on corticotroph cells.
Journal of Endocrinology (1990) 126, 183–191
Vasopressin stimulation of cell proliferation in the rat pituitary gland in vitro
Authors: McNicol A. M. , Murray J. E. , McMeekin W. 
Published: December 2008

ABSTRACT
Proliferative activity was measured in rat anterior pituitary cells in short-term culture by calculating the labelling index (LI), based on the immunohistochemical detection of cells incorporating the thymidine analogue bromodeoxyuridine. Basal LI was reproducible in the test system. Arginine vasopressin (AVP) induced a dose-related increase in LI up to 20 ng/ml. Corticotrophin-releasing factor-41 (CRF-41) had no effect at doses up to 20 ng/ml. However, in the presence of 10 ng CRF-41/ml, AVP induced a greater increase in LI at lower doses than did AVP alone. Fibroblast growth factor also induced a significant increase in LI. In the system used, epidermal growth factor and insulin had no effect on proliferation.
Journal of Endocrinology (1990) 126, 255–259
Flow cytometric analysis of functional anterior pituitary cells from female rats
Authors: Wynick D. , Venetikou M. S. , Critchley R. , Burrin J. M. , Bloom S. R. 
Published: December 2008

ABSTRACT
Laser-light scatter signals generated from living cells provide useful information with regard to both cell size (forward-angle light scatter) and granularity (ninety-degree or perpendicular light scatter). By measuring angles of light scatter and fluorescence, a fluorescence-activated cell sorter is capable of analysing and sorting cells on the basis of their size, granularity and cell-surface fluorescence. Using an electronically programmable individual cell sorter we were able to analyse single, viable, dispersed anterior pituitary cells of the female rat on the basis of their laser light scatter characteristics. Two distinct populations of differing granularity were defined: 26±2·2% (mean ± s.e.m.) were more granular and 74±3·5% less granular. Acutely dispersed anterior pituitary cells were labelled with antibodies against four of the anterior pituitary hormones, and cell size and granularity were compared amongst the different hormonal cell types. Somatotrophs were the most granular cell type, gonadotrophs were the largest and corticotrophs the smallest, whilst lactotrophs were of intermediate size. Labelling was demonstrated to be dependent upon the secretory state of the cell. Hypothalamic stimulating factors increased cell-surface labelling, whilst dopamine and somatostatin decreased labelling. These changes compare favourably with published data obtained by immunocytochemistry. Using dual-colour fluorescence cell surface labelling we were unable to define a population of cells secreting both prolactin and growth hormone (mammosomatotrophs).
Journal of Endocrinology (1990) 126, 261–268
Extracellular ATP-induced production of hydrogen peroxide in porcine thyroid cells
Authors: Nakamura Y. , Ohtaki S. 
Published: December 2008

ABSTRACT
Hydrogen peroxide (H2O2) is an essential substrate for the peroxidase reaction in thyroid hormone biosynthesis. We demonstrated the production of H2O2 from porcine thyroid cells stimulated with extracellular ATP, using a scopoletin–horseradish peroxidase (HRP) system. Incubation of isolated cells for 1 day in the presence of 10% (v/v) newborn calf serum was necessary for the detection of induction by ATP of H2O2 production. The rate of H2O2 production induced by the addition of ATP increased in a dose-dependent manner, and the concentration of ATP required for half-maximum stimulation was about 10 μmol/l. ADP and GTP were also effective, but only at higher concentrations than ATP. In the absence of extracellular Ca2+, the production rate was very low.
Production of H2O2 from thyroid cells was also measured by a method which discriminated between H2O2 and superoxide anion (O2−); in this, diacetyl-deuteroheme-substituted HRP was employed as the trapping agent for both O2 metabolites. The thyroid cells produced H2O2, but not O2−, when the cells were stimulated by extracellular ATP.
Journal of Endocrinology (1990) 126, 283–287
FSH causes a time-dependent stimulation of preovulatory follicle growth in the absence of pulsatile LH secretion in ewes chronically treated with gonadotrophin-releasing hormone agonist
Authors: Picton H. M. , Tsonis C. G. , McNeilly A. S. 
Published: December 2008

ABSTRACT
The study investigated the relationship between the plasma concentration of FSH and the stimulation of preovulatory follicle growth in vivo in ewes chronically treated with the gonadotrophin-releasing hormone (GnRH) agonist buserelin (HOE 766). Welsh Mountain ewes with regular oestrous cycles were treated for 6 weeks with two discs implants placed s.c., each containing 5 mg of the agonist in a matrix of polyhydroxybutyric acid. Treatment with the agonist for 35 days produced a sustained suppression of the plasma concentration of FSH, stopped the pulsatile release of LH and prevented follicular development beyond 2·5 mm diameter. There was no difference between the total number of follicles > 1·0 mm diameter present in the ovaries of GnRH agonist-treated ewes and day 8 luteal phase control ewes.
During the sixth week of agonist treatment ewes were infused with ovine FSH (6 μg NIADDK-oFSH16/h) in the presence of only basal concentrations of LH. After 24, 48, 72 or 120 h of FSH infusion, the mean number of follicles > 1 ·0 mm diameter per ewe was not significantly different between treated and control animals. Infusion of FSH caused a timedependent increase in (1) the number of follicles per ovary >2·5 mm, (2) the mean diameter of these follicles and (3) the proportion of the large follicles which could be classified as oestrogenic (> 3·7 nmol oestradiol/follicle per h in vitro). Injection of human chorionic gonadotrophin (750IU i.m.) after 120 h of FSH infusion caused the majority of these large follicles to ovulate and form apparently normal corpora lutea. These results indicate that, in the absence of pulsatile LH, FSH stimulates the growth of normal large oestrogenic follicles which, when stimulated, ovulate to produce viable corpora lutea.
Journal of Endocrinology (1990) 126, 297–307
Evidence that desensitization of the negative feedback of oestrogen and priming for the positive feedback of oestrogen depend upon a common mechanism of oestrogen action in rats
Authors: Döcke F. , Rohde W. , Stürzebecher B. , Ledwon P. , Dörner G. 
Published: December 2008

ABSTRACT
Oestrogen priming of the central nervous system is required for the positive feedback of oestrogen, and the sensitivity of the negative feedback of oestrogen can be reduced by oestrogen itself. Using adult female and male rats we examined the possibility that these effects depend upon a common mechanism of oestrogen action that is mediated by the medial preoptic area (MPOA). Guide cannulae were implanted in the MPOA of 4-day cyclic rats which were ovariectomized during the evening of day 1 of dioestrus. Glass capillary tubes containing different substances were placed in the cannulae between 09.00 and 12.00 h on the presumptive day 2 of dioestrus. The effectiveness of oestrogen priming was evaluated by examining whether an s.c. implant of oestradiol-17β (OE2) induced an LH surge, and the inhibitory effect of oestrogen on tonic LH secretion was investigated by injecting the rats with 3 μg oestradiol benzoate (OB)/100 g body weight.
The priming effect of an s.c. implant of OE2 could be imitated by the bilateral implantation in the MPOA of a mixture of OB and cholesterol at a ratio of 1:360 for 3 h only. Similar medial preoptic oestrogen implantation also significantly reduced the LH-inhibiting effect of OB. In accord with findings obtained in former studies on desensitization of the negative oestrogen feedback, oestrogen priming resulting from the s.c. administration of OE2 could be suppressed by short-term medial preoptic implantation of clomiphene citrate or apomorphine; bilateral electrical stimulation of the medial amygdaloid nucleus induced an increase in the serum concentration of LH in ovariectomized females implanted with OB in the MPOA, but not in castrated males pretreated and implanted with OB.
The data are compatible with the hypotheses (1) that desensitization of the negative feedback and priming for the positive feedback of oestrogen depend, at least partly, upon a common mechanism of oestrogen action in rats, (2) that slight increases in the medial preoptic oestrogen concentration on the morning of the day of dioestrus create changes which evoke both completion of maturation of preovulatory follicles and ovulation, and (3) that one object of oestrogen priming may be to facilitate the passage of oestrogen-induced neural stimuli from the medial amygdala to the median eminence.
Journal of Endocrinology (1990) 126, 395–402
Islet amyloid polypeptide-like immunoreactivity (amylin) in rats treated with dexamethasone and streptozotocin
Authors: Jamal H. , Bretherton-Watt D. , Suda K. , Ghatei M. A. , Bloom S. R. 
Published: December 2008

ABSTRACT
Islet amyloid polypeptide (IAPP) is a 37 amino acid peptide present in pancreatic β-cells. Pancreatic and circulating IAPP concentrations in rat models of diabetes were measured using a specific radioimmunoassay. Pancreatic IAPP-like immunoreactivity (IAPP-IR) in dexamethasone-treated rats was twice that of the control rats (1571±137 vs 657±176 (s.e.m.; n= 6) pmol/g), and this was reflected by similar changes in the plasma IAPP-IR (272±17 vs 102±10 pmol/l). In streptozotocin-treated rats, pancreatic IAPP-IR (200±90 pmol/g) was reduced compared with controls. There was a significant positive correlation between pancreatic and plasma IAPP-IR and insulin, with r values of 0·82 and 0·91 for the plasma and pancreas respectively. Characterization of pancreatic immunoreactivity, using gel chromatography, revealed two peaks of IAPP-IR, one which coeluted with synthetic human amidated IAPP and another peak, presumably a fragment or breakdown product, which eluted later. Chromatography of the plasma IAPP-IR revealed that >90% of the IAPP-IR eluted in the void volume, although the remaining IR coeluted with the synthetic IAPP standard. These results are not straightforwardly compatible with the suggested role for IAPP as a hormonal, paracrine or autocrine inhibitory regulator of insulin secretion in the maintenance of carbohydrate homeostasis.
Journal of Endocrinology (1990) 126, 425–429
Effect of dihydrotestosterone on serum concentrations of α2u-globulin and on spermatogenesis in melatonin-treated rats
Authors: Mandal H. , Ghosh P. K. , Biswas N. M. 
Published: December 2008

ABSTRACT
Adult male rats were given s.c. injections of melatonin (400 μg/100 g body weight per day) for 14 days. On day 15, the weights of the testis and accessory sex organs were less, testicular 17β-hydroxysteroid dehydrogenase (17β-HSD) activity was inhibited, spermatogenesis was suppressed and serum levels of gonadotrophins, testosterone and α2u-globulin were decreased compared with control animals injected with vehicle. In a third group of rats given the same dose of melatonin for 14 days, administration of dihydrotestosterone (DHT) at a dose of 25 μg/100 g body weight per day on days 8–14 resulted in serum levels of α2u-globulin, FSH, LH and testosterone and testicular 17β-HSD activity similar to those seen in vehicle-injected control animals. Weights of the testes and accessory sex organs and spermatogenesis were normal after administration of DHT in melatonintreated rats. In another group of rats, the depressive effects of melatonin treatment on plasma gonadotrophins were reversed by the administration of α2u-globulin on days 8–14. It was concluded that treatment with DHT prevents the depressive action of melatonin on testicular function by inducing the synthesis of α2u-globulin.
Journal of Endocrinology (1990) 126, 431–435
Localization of the growth hormone receptor/binding protein in skin
Authors: Lobie P. E. , Breipohl W. , Lincoln D. T. , García-Aragón J. , Waters M. J. 
Published: December 2008

ABSTRACT
Acromegaly is characterized by coarsening of facial features, acanthosis nigricans, hypertrichosis and oily skin. To determine the site through which GH exerts these effects, we have used immunohistochemistry to localize the GH receptor/binding protein (BP) in rat, rabbit and human skin. Three monoclonal antibodies (MAb 1, 43, 263) were immunoreactive in identical locations, whereas no immunoreactivity was evident when control monoclonal antibodies (MAb 50.8 and MAb 7 (rat)) were used. Skin from neonatal and adult animals was used to determine whether GH receptor/BP expression was developmentally regulated.
Immunoreactivity of the GH receptor/BP in the three species was consistently localized in the stratum basale and stratum spinosum. Intermittent staining was observed in the stratum granulosum. Scattered basal epidermal cells often displayed more intense immunoreactivity. This distribution was observed at all maturational stages examined. Intense GH receptor/BP immunoreactivity was observed in all histological layers of the lower one-third of hair follicles and in hair matrix cells of the dermal papillae. Immunoreactivity was also detected in the outer epithelial root sheath of the upper two-thirds of hair follicles, in sebaceous glands and in fibroblasts of the connective tissue sheath surrounding the follicle. GH receptor/BP immunoreactivity was also present in the secretory duct and myoepithelial cells of human eccrine sweat glands. Fibroblasts, Schwann cells of peripheral nerve fascicles, skeletal muscle cells and adipocytes of the dermis were also immunoreactive as were medial smooth muscle and endothelial cells of arteries.
These results provide evidence that GH acts locally on the epidermis and epidermal appendages concordant with our recent localization of GH receptor/BP to epithelial cell types of the gastrointestinal and reproductive systems.
Journal of Endocrinology (1990) 126, 467–472
Evidence that the action of calcitonin on rat osteoclasts is mediated by two G proteins acting via separate post-receptor pathways
Authors: Zaidi M. , Datta H. K. , Moonga B. S. , MacIntyre I. 
Published: December 2008

ABSTRACT
Calcitonin inhibits osteoclastic bone resorption and its action involves two separate acute effects on the osteoclast, both essential to the action of the hormone: abolition of cell motility (Q) and marked cellular retraction (R). The former was mimicked by dibutyryl cyclic AMP and cholera toxin and the latter by pertussis toxin, ionomycin and increases in ambient calcium. Aluminium fluoride ions produced both Q and R effects, while lithium prevented both. In addition, calcitonin elicited a biphasic elevation of cytosolic-free calcium in single isolated osteoclasts. We propose that the action of calcitonin is mediated by at least two G proteins, one responsible for the Q effect and the other for the R effect. In addition, two second messengers, cyclic AMP and calcium, are involved. These findings may help to explain the potency of calcitonin in inhibiting bone resorption, and may allow the rational design of new therapeutic agents designed to alter osteoclast behaviour.
Journal of Endocrinology (1990) 126, 473–481
DIRECT GONADOTROPHIC EFFECT OF GROWTH HORMONE ON OESTRADIOL PRODUCTION BY HUMAN GRANULOSA CELLS IN VITRO
Authors: Mason H D , Martikainen H , Beard R W , Anyaoku V , Franks S 
Published: December 2008

ABSTRACT
In-vitro studies in both rodents and man suggest that GH can stimulate ovarian steroidogenesis, but it is not clear whether this effect is mediated by changes in circulating concentrations of insulin-like growth factor-1 (IGF-1) or whether it is a direct action on the ovary (or, indeed, both). In this study the effects of biosynthetic human GH (hGH) on the production of oestradiol and IGF-1 by human granulosa cells in culture were examined using ovarian tissue (from both normal and polycystic ovaries) which had not previously been exposed to exogenous gonadotrophin therapy. Addition of hGH (1 or 10ng/ml) to the incubation medium resulted in a significant (1.7 to 3.6 fold) increase in oestradiol accumulation after 48h in culture. Human GH also had a significant additive effect on the dose-related responsiveness of granulosa cell oestradiol production to hFSH. Concentrations of IGF-1 in the medium were undetectable in each of these experiments. These studies demonstrate that hGH has a potent, direct stimulatory effect on production of oestradiol by the human ovary which is independent of the effect of FSH. These findings have important implications for understanding the physiological role of hGH in human ovarian function as well as for therapeutic use of biosynthetic hGH for induction of ovulation.
Synthetic parathyroid hormone-related peptide(1–34) fragment stimulates placental calcium transfer in ewes
Authors: Barlet J. P. , Davicco M.-J. , Coxam V. 
Published: December 2008

ABSTRACT
The influence of synthetic parathyroid hormone related peptide (PTHrp) fragments on placental transfer of Ca was studied in four groups of four single ovine fetuses fitted with catheters chronically implanted into their left jugular vein (for injections) and carotid artery (for blood sampling), and used between days 104 and 118 of gestation. The first group received PTHrp(1–34), the second PTHrp(107-138), the third bovine PTH(1–34), and the last (control) group was injected with solvent alone. Each peptide (6 nmol/fetus per day) was injected i.v. three times per day from day 105 until day 116 of gestation. Placental Ca transfer (mmol/24 h per kg fetal wt) from the dam to the fetus was not different in control fetuses 7·1±0·6) and those given PTHrp(107–138) (7·2±0·5), but it was significantly increased by bovine PTH(1–34) (8·6±0·4; P < 0·05) and by PTHrp(1–34) (10·1±0·3; P < 0·01). Both peptides also significantly increased plasma concentrations of 1,25 dihydroxy-vitamin D3 (1,25-(OH)2D). These results indicate that PTHrp(1–34) can stimulate placental Ca transfer by increasing 1,25-(OH)2D synthesis, but also possibly by acting directly upon the placenta.
Journal of Endocrinology (1990) 127, 33–37
Hypothyroidism affects reproductive refractoriness and the seasonal oestrous period in Welsh Mountain ewes
Authors: Follett B. K. , Potts C. 
Published: December 2008

ABSTRACT
Welsh Mountain ewes (n = 6) were rendered hypothyroid by daily treatment with methylthiouracil (35 mg/kg), beginning in early August and ending in late February. Plasma thyroxine levels were reduced by mid-September to about 33% of those in untreated ewes (n = 6). The two groups of ewes were held under natural daylengths until 5 October, then on 12 h light:12 h darkness (12L:12D) until 28 February when the photoperiod was reduced to 8L:16D. The onset of reproductive cyclicity in October was similar in both groups of ewes but the end of the reproductive period occurred later (P < 0·05) in the hypothyroid ewes (29 January±7 days (s.e.m.)) than in the untreated controls (6 January±7 days). As a result, the duration of the seasonal reproductive period was significantly (P < 0·05) longer in the hypothyroid (122±9 days) than in the untreated ewes (91±10 days). The number of oestrous cycles (duration 15·4 and 15·7 days in the hypothyroid and untreated ewes respectively) was 7·0±0·6 in the hypothyroid ewes and 5·0±0·5 (P < 0·05) in the normal ewes. Reducing the photoperiod overcame the reproductive refractoriness and anoestrus in both groups, the hypothyroid ewes beginning to cycle on 13 April (±0·5 days) after an anoestrous period of 72·8±7·1 days. The untreated ewes began to cycle 2 weeks later on 26 April (±1·7 days) after an anoestrous period of 112·0±8·5 days (P < 0·001).
Hypothyroidism appears, therefore, to affect the development of the refractoriness which ends the reproductive season in the sheep as well as its intensity. Such effects are similar to those found after full thyroidectomy but less pronounced since thyroidectomy is able to suspend anoestrus completely.
Journal of Endocrinology (1990) 127, 103–109