bluuebunny/crossref_metadata_2025 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

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

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

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

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

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

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

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

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

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

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

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

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

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
Metabolic effects of cortisol, ACTH, adrenalin and insulin in the marsupial sugar glider, Petaurus breviceps
Authors: Bradley A. J. , Stoddart D. M.
Published: December 2008

The effects of cortisol, ACTH, adrenalin and insulin on indices of carbohydrate, fat and protein metabolism were investigated in the conscious marsupial sugar glider Petaurus breviceps.

Short-term i.v. infusion of cortisol at dose rates of 0·02, 0·2 and 1·0 mg/kg per h caused the plasma glucose concentration to rise sharply from the normal range of 3·3–4·4 to 8·1–8·7 mmol/l at the end of the infusion period without significant alteration in plasma free fatty acid (FFA), amino acid or urea concentrations. Infusions of ACTH at dose rates of 0·02, 0·06 and 0·45 IU/kg per h caused a similar rise in plasma glucose concentration; however, this was now accompanied by an elevation in plasma FFA concentration, but again without significant changes in either plasma amino acid or urea concentrations. Infusion of adrenalin at 10 μg/kg per h caused an increase in the plasma concentrations of both glucose and FFA. Intravenous injections of 0·15 IU insulin/kg caused a rapid and marked decrease in the plasma glucose concentration within 30 min and an increase in the plasma free cortisol concentration. Associated with this change was a marked rise in the plasma concentration of both FFA and free cortisol. The rise in free cortisol was, however, significantly reduced by infusion of glucose. Pretreatment with five daily i.m. injections of 1 mg cortisol acetate/kg, which produced an increase in plasma free cortisol concentration to near the maximum of the physiological range, caused a marked reduction in insulin sensitivity. Cortisol pretreatment caused an increase in the plasma FFA and amino acid concentrations.

Petaurus breviceps is highly sensitive to the metabolic effects of glucocorticoids and is similar in this respect to the brush-tailed possum Trichosurus vulpecula. The interactive effects between insulin and glucocorticoids on carbohydrate, fat and protein metabolism in Petaurus breviceps are similar to those shown by Trichosurus vulpecula and some eutherian mammals but contrast with the pattern described for two macropodid marsupials, the red kangaroo Macropus rufus and the quokka Setonix brachyurus.

Journal of Endocrinology (1990) 127, 203–212
Characterization of insulin-like growth factor-binding protein in ovine amniotic fluid
Authors: Wang J.-F. , Fraher L. J. , Hill D. J.
Published: December 2008

We have characterized an insulin-like growth factor (IGF)-binding protein present in ovine amniotic fluid. Using an activated charcoal-binding assay, whole amniotic fluid specifically bound approximately 20–30% of 125I-labelled human (h) IGF-II added, while the binding of 125I-labelled hIGF-I was minimal. Radioimmunoassay for IGF-I or -II in ovine biological fluids showed that values in amniotic fluid were 9- to 13-fold less than in fetal plasma, while gel filtration of amniotic fluid on Sephadex G-50 eluted with 1 mol acetic acid/l revealed no additional binding activity which had been complexed to IGFs at neutral pH. Together, these observations suggest that the binding activity in amniotic fluid is largely unsaturated. Competition studies for the displacement of 125I-labelled IGF-II binding to amniotic fluid by increasing amounts of unlabelled IGF-I or -II, using the charcoal assay, showed that IGF-II was 30-fold more potent than IGF-I. Scatchard analysis revealed a single class of binding site for IGF-II, with a binding affinity of 0·68 ±0·18 litres/nmol (mean ± s.d., n = 3). Ligand blot analysis of amniotic fluid by separation on 8% SDS-PAGE, transfer to nitrocellulose membranes, incubation with 125I-labelled IGF-II and autoradiography revealed a single band of IGF-binding protein with approximate molecular size of 38 kDa. Additional IGF-binding species of 20, 28, 48 and > 180 kDa were present in ovine fetal plasma. Separation of amniotic fluid on Concanavalin A–Sepharose revealed that it had little carbohydrate content. These results show that ovine amniotic fluid contains an unsaturated, non-glycosylated IGF-binding protein with high affinity for IGF-II. These characteristics differ from those of the IGF-binding proteins purified from human amniotic fluid.

Journal of Endocrinology (1990) 127, 325–333
Cytosolic glucocorticoid receptors in the porcine lung during development and after hypophysectomy or thyroidectomy
Authors: Yarney T. A. , Kendall J. Z. , Randall G. C. B.
Published: December 2008

The ontogeny of fetal lung glucocorticoid receptors and their regulation by the fetal pituitary, adrenal and thyroid gland during lung maturation were investigated. Sites with a specificity typical of glucocorticoid receptors were detectable in lung cytosol, with the order of potency of steroids being dexamethasone > cortisol > corticosterone > 11- -deoxycorticosterone > progesterone > 17α-hydroxyprogesterone > oestradiol -17β ≃ testosterone ≃ androstenedione ≃ oestrone. The binding affinity for [3H]dexamethasone was high (Kd = 0·23–0·60 nmol/l) and showed an age-related decrease during the perinatal period when cortisol levels were high. After charcoal treatment of the cytosol, however, a decrease in binding affinity was not as clearly evident. The Kd decreased following hypophysectomy of fetuses; thyroidectomy had no significant effect. The concentration of glucocorticoid receptors was high from day 82 to day 100 of gestation (1437 fmol/mg protein) and declined progressively to a lower value at term and following birth (660 fmol/mg protein). Hypophysectomy, but not thyroidectomy, prevented the age-related decline in receptor concentration. Lung glycogen content declined with fetal ageing in association with increases in plasma concentrations of cortisol and thyroxine and with changes in Kd and Bmax, but appeared to be more closely associated with concentrations of thyroxine. Hypophysectomy of fetuses decreased concentrations of both cortisol and thyroxine and prevented the depletion of lung glycogen content. Preliminary results from thyroidectomized fetuses showed decreases in plasma thyroxine and lung glycogen content compared with day-82 fetuses. Plasma cortisol levels, however, were consistent with a fetal age of 113 days. The effects of thyroxine on lung glycogen depletion, therefore, appear to occur, at least in part, through a pathway independent of glucocorticoid receptors.

Journal of Endocrinology (1990) 127, 341–349
Regulation of interleukin-6 release by human thyrocytes
Authors: Weetman A. P. , Bright-Thomas R. , Freeman M.
Published: December 2008

Autoimmune thyroiditis is characterized by lymphocytic accumulation within the thyroid which may be the result, in part, of immunomodulatory cytokine secretion by thyrocytes. We have tested human thyroid cell cultures (n = 9) for interleukin-6 (IL-6) release using two bioassays. IL-6 was detected in all culture supernatants under basal conditions and was increased by γ-interferon, tumour necrosis factor and TSH in a dose-dependent manner. The bioactivity was confirmed as IL-6 by immunoblotting experiments and could not be accounted for by contamination of the thyroid cell cultures with fibroblasts, lymphocytes or monocytes. Circulating IL-6 levels were not raised in patients with Graves' hyperthyroidism. Exogenous recombinant IL-6 reduced cyclic AMP production in response to TSH when added to thyroid cell cultures. Since IL-6 plays a major role in B cell differentiation and T cell activation, release of IL-6 by thyrocytes may increase the intrathyroidal autoimmune response in Graves' disease and Hashimoto's thyroiditis. Our results also suggest that IL-6 may modulate thyroid cell function.

Journal of Endocrinology (1990) 127, 357–361
The influence of adrenal hormone status on neuroendocrine peptides in the rat anterior pituitary gland
Authors: Jones P. M. , O'Halloran D. J. , Ghatei M. A. , Domin J. , Bloom S. R.
Published: December 2008

Neuropeptide Y (NPY), neurotensin (NT), substance P (SP) and vasoactive intestinal peptide (VIP) are four structurally unrelated neuroendocrine peptides which affect anterior pituitary function. All four peptides appear to be locally synthesized in the anterior pituitary gland and have been shown to be regulated by thyroid and/or sex hormone status. We show here that NT, SP and VIP but not NPY are influenced by adrenal hormone status in the male rat pituitary gland. Adrenalectomy increased the content of VIP (35·4±4·0 (s.e.m.) vs control 11·9±1·1 pmol/g wet weight) but decreased that of SP (18·8±2·3 vs control 36·7 ±3·9 pmol/g wet weight). Adrenalectomy combined with castration decreased the content of SP (14·6±3·5 vs control 36·7±3·9 pmol/g wet weight) but had no effect on VIP content. Treatment with dexamethasone produced significant decreases in NT, SP and VIP contents (17·8±2·3 vs control 32·6±3·4 pmol/g wet weight, 5·5±0·9 vs control 36·7±3·9 pmol/g wet weight and 4·2±0·6 vs control 11·9±1·1 pmol/g wet weight respectively). The changes in pituitary peptide contents occurred in parallel with changes in mRNA levels, suggesting that alterations in glucocorticoid hormone status can alter the synthesis of these peptides. These results, together with the known effects of these neuroendocrine peptides suggest possible functions for locally produced SP and VIP in regulating the secretion of adrenocorticotrophin and/or other proopiomelanocortin-derived peptides. The differential effects of adrenalectomy and adrenalectomy combined with castration on VIP suggests that the regulation of this pituitary peptide is complex, and may be dependent, in part at least, on gonadal factors.

Journal of Endocrinology (1990) 127, 437–444
The adult dogfish (Scyliorhinus canicula L.) testis: a model to study stage-dependent changes in steroid levels during spermatogenesis
Authors: Sourdaine P. , Garnier D. H. , Jégou B.
Published: December 2008

The unit structure of the testis of Scyliorhinus canicula L. is the seminiferous lobule arranged in topographically distinct zones and comprised of cysts formed by steroid-producing Sertoli cells associated with germ cells at an identical stage of spermatogenesis. In this experiment, testicular tissues from different dogfish corresponding to the zones of lobules with spermatogonia (A), spermatocytes (B), early spermatids (C) and late spermatids (D) were dissected out and pooled. They were either used for steroid radioimmunoassay or incubated to measure steroid production in response to dogfish pituitary extract or to dibutyryl cyclic AMP (dbcAMP). Our results indicate that testosterone is the main testicular androgen in this species. Furthermore, marked changes in the distribution of steroids were observed according to the zone of spermatogenesis, testosterone concentrations being highest in zones A and D. The relative contents of this hormone (steroid levels normalized to an equivalent number of Sertoli cells) as well as of Δ4-androstenedione and of progesterone increased from A to D. The concentrations of Δ4-androstenedione and progesterone were highest in zone D. Relative contents of 5α-androstane-3α,17β-diol, dihydrotestosterone and 11-ketotestosterone were very low in A when compared with the other zones. Finally, whereas no significant stage-related variation in the concentration of oestradiol-17β and 17α-hydroxy, 20β-dihydroprogesterone was observed, the relative content of these steroids was lowest in zone A. Incubation experiments revealed that dogfish pituitary extract and dbcAMP can stimulate androgen synthesis (about twofold) and that a stage-related change of steroid responsiveness to dbcAMP exists (only zones A and D were responsive). Overall, the results of this study indicate that germ cells most probably influence Sertoli cell steroidogenesis and responsiveness in the adult dog fish testis.

Journal of Endocrinology (1990) 127, 451–460
Responses to protein deficiency of plasma and tissue insulinlike growth factor-I levels and proteoglycan synthesis rates in rat skeletal muscle and bone
Authors: Yahya Z. A. H. , Bates P. C. , Millward D. J.
Published: December 2008

The relative biological importance of plasma levels of insulin-like growth factors (IGFs) is uncertain since the IGFs may act through endocrine mechanisms involving circulating IGFs secreted by the liver, or by autocrine/paracrine mechanisms with IGF production in or close to their target cells. We report here studies in rats designed to examine this problem with an investigation of the changes in plasma and tissue concentrations of IGF-I in relation to the inhibition of bone and muscle growth and proteoglycan synthesis, a putative IGF-I-sensitive process, by protein deficiency. Over a 3-week period in young well-fed growing rats, there were marked increases in plasma IGF-I, whereas in the protein-deficient animals in which growth was inhibited concentrations fell markedly. In bone, concentrations of IGF-I were initially 20% of plasma, did not increase with age and were minimally influenced by protein deficiency. In skeletal muscle, concentrations of IGF-I were initially 3% of plasma, did not increase with age, but did fall with protein deficiency. In bone, the inhibition of proteoglycan synthesis by the protein deficiency was not correlated with changes in tissue IGF-I concentrations and was poorly correlated with changes in plasma hormone concentrations, although in the latter case an exponential relationship could be fitted to the data from the initial control and subsequent protein-deficient animals. In muscle, the changes in proteoglycan synthesis were significantly linearly correlated with changes in tissue IGF-I compared with an exponential relationship with plasma concentrations from the initial control and subsequent protein-deficient animals. These data demonstrate that neither plasma IGF-I concentrations nor the level of total extractable tissue IGF-I can be assumed to be unequivocal determinants of IGF-I status.

Journal of Endocrinology (1990) 127, 497–503
RAT MELANIN CONCENTRATING HORMONE DOES NOT MODIFY THE RELEASE OF CRH-41 FROM RAT HYPOTHALAMUS OR ACTH FROM THE ANTERIOR PITUITARY IN VITRO
Authors: Navarra P. , Tsagarakis S. , Coy D. H. , Rees L.H. , Besser G. M. , Grossman A. B.
Published: December 2008

It has been suggested that melanin concentrating hormone (MCH) possesses potent corticotrophin (ACTH) inhibitory activity, on the basis of the inhibitory effects displayed by salmon MCH on ACTH release from either trout or rat isolated pituitary fragments. Recently, rat MCH has been characterised, and this prompted us to investigate the putative inhibitory activity of synthetic rat MCH on basal and stimulated ACTH secretion from freshly-dispersed rat pituitary cells or incubated rat pituitary fragments, as well on KCl (28 mmol/l) or noradrenaline-evoked release of corticotrophin releasing hormone-41 (CRH-41) from rat hypothalamic explants in vitro. There were no effects of rat MCH on either CRH-41 or ACTH release in vitro.
Identification of 11,13-dihydroxy-14-octadecaenoic acid as a circulating Na+/K+-ATPase inhibitor
Authors: Lichtstein D. , Samuelov S. , Gati I. , Felix A. M. , Gabriel T. F. , Deutsch J.
Published: December 2008

Two digitalis-like compounds (DLC) were purified to homogeneity from bovine plasma. The purification procedure consisted of organic extractions and batch chromatography followed by three subsequent separations using reverse-phase high-performance liquid chromatography. The presence of a DLC in the different fractions was monitored by their ability to inhibit (a) [3H]ouabain binding to rat brain synaptosomes, and (b) microsomal Na+/K+-ATPase activity. Using mass spectrometry and nuclear magnetic resonance spectroscopy the structure of one of the DLCs was identified as 11,13-dihydroxy-14-octadecaenoic acid. It is suggested that this new hydroxy, unsaturated, fatty acid derivative may regulate Na+/K+-ATPase activity under some physiological and pathological conditions.

Journal of Endocrinology (1991) 128, 71–78
Effects of full-length and truncated insulin-like growth factor-I on nitrogen balance and muscle protein metabolism in nitrogen-restricted rats
Authors: Tomas F. M. , Knowles S. E. , Owens P. C. , Read L. C. , Chandler C. S. , Gargosky S. E. , Ballard F. J.
Published: December 2008

The ability of insulin-like growth factor-I (IGF-I) to protect against losses of body protein during periods of dietary nitrogen restriction has been evaluated in young rats. Recombinant human IGF-I was administered by osmotic pumps at dose rates of 0, 1·2 or 2·9 mg/kg per day over a 7-day period beginning with the transfer of animals from an 18% to a 4% protein diet. A fourth group received the potent truncated IGF-I analogue, des(1–3)IGF-I, at a dose of 1·2 mg/kg per day over a comparable 7-day period. Plasma IGF-I levels were reduced by 60% following nitrogen restriction, a reduction that was partly prevented by IGF-I administration, especially at the higher dose, but not measurably by des(1–3)IGF-I. The major IGF-binding protein circulating in blood, IGFBP-3, demonstrated a similar pattern of change.

A significant (P<0·05) protection of body weight was achieved in the low dose IGF-I and des(1–3)IGF-I groups, but only after differences in food intake had been eliminated by analysis of covariance. Nitrogen balances were not significantly different unless analysis of covariance was used to adjust for the nitrogen intakes, whereupon all treatment groups showed improved balance, especially the animals treated with the low IGF-I dose and des(1–3)IGF-I (both P<0·01). The rate of muscle protein breakdown calculated from the urinary excretion of 3-methylhistidine was not significantly altered by the treatments, but fell progressively throughout the 7 days. The fractional rate of muscle protein synthesis measured on the final day was increased by 31, 26 and 21% respectively by the low and high doses of IGF-I and by des(1–3)IGF-I. Organ weights (g/kg body weight) showed no effects of IGF-I treatment except for 16% increases in the weight of kidneys in the high dose IGF-I and the des(1–3)IGF-I groups. Carcass analyses demonstrated higher water and lower fat contents (all P< 0·01) in the same groups. These results suggest that exogenous IGF-I and especially des(1–3)IGF-I can partly protect body protein reserves during nitrogen restriction.

Journal of Endocrinology (1991) 128, 97–105
Purification and assay of insulin-like growth factor-binding protein-1: measurement of circulating levels throughout pregnancy
Authors: Wang H. S. , Perry L. A. , Kanisius J. , Iles R. K. , Holly J. M. P. , Chard T.
Published: December 2008

Insulin-like growth factor-binding protein-1 (IGFBP-1) has been purified from amniotic fluid by anion exchange, hydrophobic interaction and gel filtration chromatography. The overall recovery of the purification process was 12·2%. The purified IGFBP-1 yielded a single band on SDS-PAGE gel but showed two bands (34 kDa and 68 kDa) on Western blot under non-reducing conditions. Polyclonal antisera were raised by immunization of sheep using the purified IGFBP-1. The best antiserum bound 50% of 125I-labelled IGFBP-1 at a final dilution of 1:500 000. A radioimmunoassay for IGFBP-1 was developed. This assay had a minimum detection limit of 5 μg/1, and was used to determine serum levels in non-pregnant and pregnant women. There was no cross-reaction with a wide variety of materials tested. Serum IGFBP-1 levels in non-pregnant individuals (33±16 (s.D.) μg/1) were found to be significantly lower than those in the second (96±64 μg/1) and third trimesters (95 ±60 μg/1) of pregnant women. During pregnancy, circulating IGFBP-1 levels increased rapidly in the first trimester and reached a peak at 12–13 weeks of gestation (107±75 μg/l). The level then remained at 80±53 to 103±70 μg/l until term.

Journal of Endocrinology (1991) 128, 161–168
Long-term effect of a sheep antiserum to rat growth hormone in vivo in rats is explained by the rat anti-sheep immunoglobulin response
Authors: Madon R. J. , Panton D. M. , Flint D. J.
Published: December 2008

A specific antiserum to rat GH (anti-rGH) raised in sheep was used in young male and lactating rats. In both models a group of rats was found which appeared to generate a low response (low responders) to the injected sheep immunoglobulin, and was characterized by the ability of the antiserum to cause inhibition of growth for more than 21 days in the male rats, and to abolish milk yield when prolactin concentrations were lowered in the females. In the groups which generated a high response to the anti-rGH (high responders), growth was retarded for only 2–3 days in male rats, with a moderate milk yield maintained in lactating animals.

The low-response animals were found to have a significantly longer half-life for circulating anti-rGH, when compared with the high-response animals. After 21 days, in the age-matched male rats, levels of anti-rGH were undetectable in the high-responders, whereas the low-response animals, which were nearly 160 g lighter, still had approximately 4·5 ml anti-rGH/1 in their circulation. This anti-rGH was still capable of neutralizing GH, as concentrations of insulin-like growth factor-I (IGF-I) were 13·6±3·5 (mean ± s.e.m.) and 76·9±2·0 nmol/l in the low-response and high-response groups respectively. The reason for these differences would appear to be that the immune response mounted by these low-response animals to the exogenous sheep immunoglobulin (i.e. rat anti-sheep) 7 days after treatment was less than 10% of that seen in the high-response group.

In male animals the concentration of IGF-I was positively correlated with growth rate.

It is concluded that the effectivenes of the anti-rGH was related to its clearance rate which in turn depended on the ability of the animal to mount an effective anti-sheep response.

Journal of Endocrinology (1991) 128, 229–237
Analysis of the receptor specificity of tolerance induction in stress versus opioid-related prolactin secretion in rats
Authors: Matton A. , Buydens P. , Finné E. , Govaerts J. , Vanhaelst L.
Published: December 2008

The effects of restraint stress and opiates on prolactin secretion in male rats have been measured. Both induced a short-lived increase in prolactinaemia. Experimental evidence indicates that both opioids and restraint stress bring about their actions by the activation of opioid receptors. When restraint stress was followed by administration of the specific κ-agonist bremazocine, a second prolactin peak was observed. In contrast, morphine (predominantly a μ-agonist) lost its prolactin-stimulating capacity when given after a period of restraint stress. This indicates cross-tolerance between restraint stress and morphine. Tolerance was overcome when the dose of morphine was doubled, and an increase in prolactin secretion could again be obtained. The cross-tolerance phenomenon argues that a common opioid receptor is involved in morphine- and restraint stress-stimulated prolactin release. In another set of experiments, in which morphine administration replaced restraint stress as a means of inducing tolerance, a second rise in prolactinaemia was seen only with bremazocine and not with a further administration of morphine. This suggests a morphine (μ) receptor-specific development of tolerance. Two consecutive administrations of bremazocine also produced tolerance, in this case for the κ-receptor. This illustrates the rapid and receptor-specific development of tolerance for the prolactin-releasing capacity of opioid compounds.

Journal of Endocrinology (1991) 128, 281–285
Intracellular dehydration in the rat made diabetic with streptozotocin: effects of infusion
Authors: Anwana A. B. , Garland H. O.
Published: December 2008

Metabolic and isotopic dilution techniques were used to investigate fluid balance and fluid volumes in rats made diabetic with streptozotocin before and after infusion. Uninfused diabetic rats had significantly (P < 0·01) lower total body water than controls (57·7±2·2 vs 65·7±1·4% (s.e.m.) fat free mass). This was due exclusively to a significantly (P < 0·001) reduced intracellular fluid volume (38·2±1·5 vs 45·4±1·4% fat free mass). Metabolic studies over the preceding 2 weeks showed that the fluid deficit in the diabetic group had resulted from a failure of the rats to increase their fluid intake to the same extent as their combined fluid losses. A 4-h saline infusion halved the fluid deficit in diabetic animals. The retained fluid was used to restore intracellular fluid volume which became comparable in diabetic and control rats (47·2±2·0 vs 46·4±1·0% fat free mass). The retention of infusate by diabetic animals to counteract their intracellular dehydration may partly explain the reduced urine output reported elsewhere in infused anaesthetized diabetic rats.

Journal of Endocrinology (1991) 128, 333–337