bluuebunny/crossref_metadata_2025_split huggingface dataset:
The luteotrophic actions of prostaglandins E2 and F2α on dispersed marmoset luteal cells are differentially mediated via cyclic AMP and protein kinase C
Authors: Michael A. E. , Abayasekara D. R. E. , Webley G. E. 
Published: December 2008

ABSTRACT
Progesterone production by dispersed luteal cells obtained from the marmoset monkey on day 14 after ovulation can be stimulated by both prostaglandin F2α (PGF2α) and its structural analogue, cloprostenol. To establish whether these responses can be attributed to cross-reaction with the prostaglandin E2 (PGE2) receptor, this study compared the involvement of cyclic adenosine-3′,5′-monophosphate (cAMP) and protein kinase C (PKC) in the luteotrophic responses to PGE2, PGF2α and cloprostenol. While all three prostaglandins stimulated similar increases in progesterone production (239·5 ± 7·9% of control; P <0·01), only PGE2 stimulated a significant increase in cAMP accumulation (373·2 ± 28·4% of control; P <0·01). This study is the first to demonstrate PKC activity in the marmoset ovary. Following down-regulation of PKC with a tumour-promoting phorbol ester, 4β-phorbol 12-myristate 13-acetate (4β-PMA), basal progesterone production was significantly increased (150·9 ± 8·2% of control; P <0·05) and the luteotrophic effects of PGF2α and cloprostenol were no longer evident, whereas the response to PGE2 was unaffected. These observations are consistent with the differential involvement of cAMP and PKC in the luteotrophic responses to PGE2 and PGF2α/cloprostenol respectively. Hence, we conclude that the luteotrophic actions of prostaglandins E2 and F2α on dispersed marmoset luteal cells are mediated via different receptors and signal transduction pathways.
Journal of Endocrinology (1993) 138, 291–298
Islet glucan-1,4-α-glucosidase: differential influence on insulin secretion induced by glucose and isobutylmethylxanthine in mice
Authors: Salehi A. , Lundquist I. 
Published: December 2008

ABSTRACT
In previous in-vivo studies we have presented indirect evidence for the involvement of islet acid glucan-1,4-α-glucosidase (acid amyloglucosidase), a lysosomal glycogen-hydrolysing enzyme, in certain insulin secretory processes. In the present combined in-vitro and in-vivo investigation, we studied whether differential changes in islet acid amyloglucosidase activity were related to the insulin secretory response induced by two mechanistically different secretagogues, glucose and isobutylmethylxanthine (IBMX). It was observed that addition of the selective α-glucosidehydrolase inhibitor emiglitate (1 mmol/l) to isolated pancreatic islets resulted in a marked reduction of glucose-induced insulin release. This was accompanied by a pronounced suppression of islet activities of acid amyloglucosidase and acid α-glucosidase, whereas other lysosomal enzyme activities, such as acid phosphatase and N-acetyl-β-d-glucosaminidase, were unaffected. Furthermore, islets first incubated with emiglitate in the presence of high (16·7 mmol/l) glucose released less insulin than untreated controls in response to glucose in a second incubation period in the absence of emiglitate. In contrast, IBMX-induced insulin release was not influenced by emiglitate although accompanied by a marked reduction of islet activities of all three α-glucosidehydrolases. Basal insulin secretion (1 mmol glucose/1) was unaffected in the presence of emiglitate. In-vivo pretreatment of mice with highly purified fungal amyloglucosidase ('enzyme replacement'), a procedure known to increase islet amyloglucosidase activity, resulted in a greatly enhanced insulin secretory response to an i.v. glucose load. The increase in insulin release was accompanied by a markedly improved glucose tolerance curve in these animals. In contrast, enzyme pretreatment did not influence the insulin response or the blood glucose levels after an i.v. injection of IBMX. The data lend further support to our hypothesis that islet acid amyloglucosidase is involved in the multifactorial insulin secretory processes induced by glucose but not in those involving direct activation of the cyclic AMP system. The results also indicate separate, or at least partially separate, pathways for insulin release induced by glucose and IBMX.
Journal of Endocrinology (1993) 138, 391–400
Effect of high-protein feed supplements on concentrations of growth hormone (GH), insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 in plasma and on the amounts of GH and messenger RNA for GH in the pituitary glands of adult rams
Authors: Clarke I. J. , Fletcher T. P. , Pomares C. C. , Holmes J. H. G. , Dunshea F. , Thomas G. B. , Tilbrook A. J. , Walton P. E. , Galloway D. B. 
Published: December 2008

ABSTRACT
Three groups of mature rams were maintained on diets of hay, hay+2% lupin or hay+2% cowpea for 11 weeks. Serial blood samples were taken at 15-min intervals for 12 h for the determination of GH and IGF-I content by radioimmunoassay and for IGF-binding protein-3 (IGFBP-3) levels by Western blotting. The rams were killed after 77 days of supplementary feeding and their pituitary glands analysed for content of GH and GH mRNA. Mean plasma GH and baseline GH levels were significantly (P<0·01) decreased in the rams fed lupin and cowpea compared with controls fed hay and GH pulse amplitude was significantly (P<0·001) decreased in the group fed the cowpea diet. The frequency of GH pulses was not significantly altered by either treatment. Plasma concentrations of IGF-I were elevated in rams fed lupin (P<0·001) or cowpea (P<0·05). IGFBP-3 levels were not significantly (P>0·05) altered by either treatment. There were no significant differences in pituitary content of GH mRNA but pituitary content of GH was increased in rams fed lupin (P<0·05) and cowpea (P=0·07). In conclusion, a high-protein diet decreases plasma GH levels and increases IGF-I without changing plasma IGFBP-3 levels in rams. Thus ongoing synthesis of GH, as indicated by the mRNA levels, may cause a build up of GH stores in the pituitary gland.
Journal of Endocrinology (1993) 138, 421–427
Interleukin-1β induces nitric oxide production by a mouse pituitary tumour cell line (AtT20/D16)
Authors: Ohta K. , Hirata Y. , Imai T. , Marumo F. 
Published: December 2008

ABSTRACT
To elucidate whether anterior pituitary cells express the nitric oxide (NO) synthase gene, we studied the synthesis of NO and the expression of NO synthase (NOS) mRNA by a mouse pituitary tumour cell line (AtT20/D16). Interleukin-1β (IL-1β) stimulated production of NO2−/NO3− (NOx) in a time-dependent manner and both NOx and cyclic GMP formation were stimulated in a dose-dependent manner by IL-1β. IL-1β-induced NOx production and intracellular cyclic GMP formation were similarly blocked by an NO synthase inhibitor, NG-monomethyl-l-arginine (LNMMA), whose effect was reversed by l-arginine, but not by d-arginine. Dexamethasone inhibited IL-1β-induced NOx production in a dose-dependent manner. A calmodulin inhibitor (W-7) showed no effect on IL-1β-induced NOx production, whereas cycloheximide and the actinomycin D completely inhibited NOx production. Northern blot analysis using cDNA for mouse macrophage-inducible NOS as a probe revealed the expression of inducible NOS mRNA in the cells only after exposure to IL-1β. Although IL-1β stimulated ACTH release from tumour cells, LNMMA failed to affect ACTH release stimulated by IL-1β. These results demonstrate for the first time that a pituitary tumour cell line (AtT20/D16) possesses cytokine-inducible and Ca2+/calmodulin-independent NOS, although NO may not be involved in ACTH release.
Journal of Endocrinology (1993) 138, 429–435
The uterine growth-promoting action of epidermal growth factor and its function in the fertility of mice
Authors: Tsutsumi O. , Taketani Y. , Oka T. 
Published: December 2008

ABSTRACT
Epidermal growth factor (EGF) levels in the submandibular glands and plasma are increased in pregnant and aged female mice. The possible role of EGF in fertility was studied in virgin and pregnant mice ranging in age from 10 to 90 weeks of age, employing sialoadenectomy, administration of EGF antibody and EGF replacement. The uterine weight in pregnant, 10-week-old, sialoadenectomized mice was significantly less than in normal mice and the administration of EGF antibody to these mice further decreased uterine weight, resulting in an increased rate of abortion. Replacement EGF treatment in the sialoadenectomized mice prevented these changes. Uterine weight was about 70 mg at 10 weeks of age, and significantly increased from 30 to 80 weeks when it reached a plateau level of 275 mg. These changes closely followed the increase in the concentration of EGF in the submandibular glands and plasma and coincided with the decline in fertility. In contrast, uterine weight in the sialoadenectomized mice decreased immediately after the operation and remained at about 50–60 mg throughout the experimental period. Pregnancy, as judged by implantation, was achieved in the sialoadenectomized mice at later ages than in the controls. These findings suggest that elevated EGF levels may have a dual function in the control of fertility via uterine growth, depending on the age of mice.
Journal of Endocrinology (1993) 138, 437–443
Isolation and characterization of human LH isoforms
Authors: Stanton P. G. , Pozvek G. , Burgon P. G. , Robertson D. M. , Hearn M. T. W. 
Published: December 2008

ABSTRACT
Thirty-nine human LH (hLH) isoforms were chromatographically separated from human pituitary extracts using a mild purification procedure which consisted of preparative isoelectric focusing, high-performance ion-exchange chromatography and immobilized metal-affinity chromatography. Twenty of these hLH isoforms were characterized by LH radioreceptor assay, SDS-PAGE and amino acid analysis, and 17 were shown to be highly purified (>90% pure). The specific activities of these hLH isoforms ranged from 1980 to 38 650 IU/mg protein in terms of the 2nd IS for human pituitary LH, based on protein content as determined by amino acid analysis. hFSH and hTSH content were <0·5% and <7·8% respectively. The purity was assessed by silver staining on SDS-PAGE. Under non-reducing conditions, a single band of apparent molecular mass 23·5–24·5 kDa was observed, whereas under reducing conditions the isoforms migrated as two distinct bands, 21·1–22·4 kDa and 18·0–20·5 kDa, probably corresponding to the α and β subunits of hLH respectively. The remaining three less pure isoform preparations (70–90% pure) contained additional bands of 16 kDa and 26·3 kDa under non-reducing conditions. All isoforms showed a low molecular mass band(s) of 11–14 kDa which was <7% of stained material as assessed by densitometry. Amino acid composition of the 17 hLH isoforms was similar to the published cDNA composition of hLH. Further fractionation of one hLH isoform (hLH IIc) on reversed-phase high-performance liquid chromatography yielded four peaks identified by N-terminal sequencing as two α and two β hLH subunits identical to their cDNA-derived N-terminal sequences. No additional sequences indicative of internal clipping of hLH were observed. The two pairs of α and β subunits probably represent two separate hLH isoforms in this preparation. It was concluded that a mild purification procedure with high recoveries for the isolation of intact hLH isoforms has been developed, and 17 isoforms of high purity suitable for further biological and physicochemical characterization have been isolated. These isoform preparations are free of other contaminating proteins, but may still contain multiple hLH-related species.
Journal of Endocrinology (1993) 138, 529–543
Effect of exogenous bovine growth hormone and ovariectomy on prepubertal mammary growth, serum hormones and acute in-vitro proliferative response of mammary explants from Holstein heifers
Authors: Purup S. , Sejrsen K. , Foldager J. , Akers R. M. 
Published: December 2008

ABSTRACT
Sixteen prepubertal Holstein Friesian heifers were used to study the effect of long-term administration of bovine GH (bGH) on mammary development in intact and ovariectomized heifers. Eight heifers were ovariectomized at 2·5 months of age. Four intact and four ovariectomized heifers received subcutaneous injection of bGH (15 mg/day) for 15 weeks starting at 176 ± 3 days of age (147 ± 3 kg body weight), while the remaining eight heifers received an equal volume of excipient. Blood samples were collected weekly from 2 months of age. Heifers were slaughtered on the day after the last injection of bGH or excipient. Mammary gland development was quantified by dissection, chemical analysis and computer tomographic scanning. Mammary growth response at the time of slaughter was examined in cultures with explants prepared from parenchyma. Histological and histoautoradiographic studies with explants were performed.
Treatment with bGH resulted in a significantly (P<0·05) smaller mammary gland because of a reduced amount of extraparenchymal tissue. Ovariectomy markedly reduced the amount of parenchymal tissue. Growth response in mammary explants showed no treatment differences, suggesting that the decreased amount of parenchyma in ovariectomized heifers was caused by a decrease in mammary cell proliferation occurring some time prior to slaughter. The histological composition of mammary parenchyma was not changed by bGH treatment. However, ovariectomy resulted in less epithelial tissue (P<0·001) and lumen (P<0·05) and more stroma (P< 0·001), expressed as percentage tissue area. Serum hormone concentrations of bGH and insulin-like growth factor-I (IGF-I) were increased by bGH treatment in both intact and ovariectomized heifers. However, despite the fact that mammary growth in ovariectomized heifers was eradicated, the serum concentration of oestradiol was only decreased by one-third compared with intact heifers.
The study therefore confirms the importance of ovarian secretions for mammary growth and development in prepubertal heifers. However, the results give no clear evidence of an interaction between ovarian secretions and GH on the regulation of the development of the mammary parenchyma in heifers.
Journal of Endocrinology (1993) 139, 19–26
Ruminants express a prolactin receptor of Mr 33 000—36 000 in the mammary gland throughout pregnancy and lactation
Authors: Smith J. J. , Capuco A. V. , Mather I. H. , Vonderhaar B. K. 
Published: December 2008

ABSTRACT
Developmental variation in the expression of the prolactin receptor in the ruminant mammary gland was investigated. Affinity chromatography revealed that bovine prolactin and human GH each bound to the same mammary gland proteins, yielding fractions enriched in binding activity and a protein of Mr 36 000, assumed to be a bovine prolactin receptor. Affinity cross-linking of 125I-labelled human GH to mammary microsomes confirmed that the Mr 36 000 protein was a bovine prolactin receptor. Binding assays of receptors in microsomes from the mammary tissue of cows and ewes at various stages of the lactational/reproductive cycle indicated developmental regulation of receptor concentration, but not receptor type, as no other bovine prolactin receptor type was detected by affinity cross-linking. These results suggest that differences in the response to prolactin in the mammary gland at various developmental stages in ruminants are not due to the expression of different forms of the prolactin receptor, and the lack of a prolactin effect on established lactation in ruminants is not due to the absence of the Mr 36 000 form of the prolactin receptor.
Journal of Endocrinology (1993) 139, 37–49
The effect of acute pharmacological manipulation of central serotonin neurotransmission on osmoregulated secretion of arginine vasopressin in the rat
Authors: Faull C. M. , Charlton J. A. , Butler T. J. , Baylis P. H. 
Published: December 2008

ABSTRACT
To explore the hypothesis that serotonin (5-HT) is important in osmoregulated arginine vasopressin (AVP) secretion, we administered (i.p.) fluoxetine (FL) a 5-HT reuptake inhibitor (10 mg/kg body weight), ritanserin (RIT), an antagonist at the 5-HT2 and 5-HT1c receptor subtypes (1 mg/kg body weight), 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI), a 5-HT2 receptor agonist (1 mg/kg body weight) or vehicle to rats 30 min before they were given an osmotic challenge. Rats received distilled water, normotonic saline (150 mmol NaCl/l) or hypertonic saline (500 mmol NaCl/l) (20 ml/kg i.p) and were killed 30 min later. The osmotic stimulus alone produced significant (P<0·001) effects on plasma osmolality and plasma sodium but FL, RIT and DOI did not have any significant effect on this stimulus. FL had no significant effect on the osmotic threshold of AVP release but significantly (P<0·001) increased basal AVP secretion from 1·6 ± 1·0 to 3·1 ± 1·3 (s.e.m.) pmol AVP/l and significantly (P<0·001) increased the AVP response to changes in plasma osmolality: vehicle-treated, 0·7 ± 0·4; FL-treated, 1·7 ± 0·2 pmol AVP/l per mOsm per kg. Neither RIT nor DOI had any significant effect on basal or stimulated AVP secretion. In a second study, RIT was administered 60 min i.p. prior to FL i.p. (doses as above), which was followed 30 min later by a hypertonic stimulus i.p. and rats were killed 30 min after hypertonic saline treatment. RIT had no significant effect on the AVP response to plasma osmolality and did not significantly alter the FL-augmented AVP response, suggesting that neither the 5-HT2 nor the 5-HT1c receptors are involved in the response of AVP to FL. We conclude that FL modulates osmoregulated AVP secretion but that the mechanism of this is unknown and is apparently not through the 5-HT2 or 5-HT1c receptor subtypes.
Journal of Endocrinology (1993) 139, 77–87
The relationship between the physicochemical properties and the biological effects of alloxan and several N-alkyl substituted alloxan derivatives
Authors: Munday R. , Ludwig K. , Lenzen S. 
Published: December 2008

ABSTRACT
Alloxan causes diabetes in experimental animals through its ability to destroy the insulin-secreting B-cells of the pancreas. Alloxan is hydrophilic and chemically unstable; it is reactive toward thiols, undergoing redox cycling in the presence of glutathione and oxidizing protein-bound thiol groups, as reflected by inhibition of the thiol enzymes, hexokinase and glucokinase. It is apparently also selectively taken up by the GLUT-2 glucose transporter in the pancreatic B-cell membrane. In order to investigate which, if any, of these physicochemical properties are important in the toxic action of alloxan, we have examined seven N-alkyl substituted alloxan derivatives of various diabetogenic activity. Hydrophilicity was identified as a factor essential for diabetogenicity. Stability, rate of redox cycling and reactivity toward thiol groups were not correlated with diabetogenicity. Selective uptake by the GLUT-2 glucose transporter is not a prerequisite for the diabetogenicity of alloxan derivatives.
Journal of Endocrinology (1993) 139, 153–163
Effects of fasting, elevated plasma glucose and plasma insulin concentrations on milk secretion in women
Authors: Neville M. C. , Sawicki V. S. , Hay W. W. 
Published: December 2008

ABSTRACT
In order to determine whether short term variations in plasma glucose and/or insulin influence milk lactose secretion in women, the effects of fasting and increased blood insulin and glucose on milk volume and composition were studied with glucose clamp methodology in exclusively and partially breast-feeding women. Twenty hours of fasting had no discernable effect on the output of milk or its macronutrient composition. Four hours of increased plasma insulin, studied under conditions where plasma glucose was maintained at the fasting level, had no effect on milk volume, milk glucose concentration, total fat content or lactose secretion rate. Increased plasma glucose, maintained at twice fasting levels for 4 to 6 h, produced a threefold increase in milk glucose concentration but had no significant effect on the rate of lactose synthesis. In partially breast-feeding women producing no more than 200 ml milk per day, a similar degree of hyperglycaemia increased milk glucose more than fourfold but did not significantly increase the milk secretion rate. It is concluded that human milk production is isolated from the homeostatic mechanisms that regulate glucose metabolism in the rest of the body, in part because the lactose synthetase system has a Km for glucose lower than the concentration available in the Golgi compartment.
Journal of Endocrinology (1993) 139, 165–173
Dopamine is taken up from the circulation by, and released from, local noradrenergic varicose axon terminals in zona glomerulosa of the rat: a neurochemical and immunocytochemical study
Authors: Vizi E. S. , Tóth I. E. , Orsó E. , Szalay K. Sz. , Szabó D. , Baranyi M. , Vinson G. P. 
Published: December 2008

ABSTRACT
The effect of supramaximal electric field stimulation on [3H]dopamine (DA) release by rat adrenal capsuleglomerulosa preparations was studied using a microvolume perfusion system. When the tissues were preloaded with [3H]DA, a considerable amount of [3H]DA and [3H]noradrenaline (NA) were released in response to field stimuli. Reserpinization, calcium removal or tetrodotoxin blocking of Na+ influx all completely inhibited the stimulation-evoked release of DA/NA, indicating that the radioactivity released is of neuronal and vesicular origin. In the adrenal cortex, a substantial proportion of tyrosine hydroxylase and dopamine-β-hydroxylase immunoreactive nerve fibres and varicosities were observed around the zona glomerulosa. DA-containing nerves were not seen in the adrenal cortex; however, the same immunocytochemical procedures clearly demonstrated dopaminergic nerve cells and fibres in the substantia nigra and the striatum respectively, and cells of the adrenal medulla. Like the NA release from noradrenergic varicosities in the zona glomerulosa, the DA release from noradrenergic endings is not subject to negative feedback modulation through DA2 receptors since apomorphine, a DA2-receptor agonist, and sulpiride, a selective DA2-receptor antagonist, failed to affect the release. After in-vivo i.v. administration of [3H]DA, the glomerulosa content of DA and NA and the in-vitro release of [3H]DA and [3H]NA of zona glomerulosa both increased, indicating that the local varicose axon terminals were able to accumulate DA from the circulation, convert it into NA and release it in response to neural activity. This local arrangement of noradrenergic axon terminals, able to take up DA from the circulation and release it or convert it into NA, provides the possibility of a fine tuning of local circulation and aldosterone synthesis in the zona glomerulosa.
Journal of Endocrinology (1993) 139, 213–226