bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age-related alterations in the response of hepatic lipogenic enzymes to altered thyroid states in the rat
Authors: Mooradian A. D. , Deebaj L. , Wong N. C. W. 
Published: December 2008

ABSTRACT
To determine the age-related alterations in tissue-responsiveness to thyroid hormone action, the mRNA levels and the enzyme activities of hepatic cytosolic malate dehydrogenase (ME) and mitochondrial α-glycerophosphate dehydrogenase (α-GPD) were determined in groups of euthyroid, hypothyroid and hyperthyroid male Fischer 344 rats at various ages. The basal α-GPD level (change in optical density/min per mg) in 2-month-old rats (0·163 ±0·003) (s.e.m.) was significantly (P < 0·001) higher than that in 6-month-old and 26-month-old rats (0·116±0·012 and 0·098±0·013 respectively). The basal ME activity (mU/mg) was significantly (P < 0·001) reduced in aged rats (9·2±0·89) compared with younger rats (54·2±3·4 and 17·1±2·3 for 2-month-old and 6-month-old rats respectively). The response of ME to tri-iodothyronine (T3) in aged rats compared with young rats was reduced approximately 50%. This age-related reduction in ME response to T3 could not be attributed to reduced food intake with ageing. Northern blot analysis showed that ME mRNA levels in hyperthyroid aged rats were 50% of those of young hyperthyroid rats. There were no significant differences in either basal or T3-stimulated α-GPD mRNA levels. The proportional reduction in steady-state ME mRNA levels and ME activity in aged rats indicates that this age-related change is modulated at a pretranslational level.
Journal of Endocrinology (1991) 128, 79–84
Pre-exposure of rat anterior pituitary cells to somatostatin enhances subsequent growth hormone secretion
Authors: Richardson S. B. , Twente S. 
Published: December 2008

ABSTRACT
The precise roles of GH-releasing factor (GRF) and somatostatin (SRIF) in the orchestration of pulsatile GH secretion have not yet been fully determined. We examined the interactions of rat GRF and SRIF, in the concentration ranges present in rat hypophysialportal blood, on the secretion of GH from dispersed male rat anterior pituitary cells in monolayer culture. The effects of exposing cells to GRF and/or SRIF (0·01–1·nmol/l) for 1 h were compared with the effects of preincubation of cells with SRIF before experimental incubations. As anticipated, the stimulatory effects of 0·1–1 nmol GRF/l were abolished by concurrent incubation with SRIF at an equimolar concentration, although SRIF, at these concentrations, did not significantly inhibit basal GH secretion. Conversely, pre-exposure to 0·1 nmol SRIF/l for 30 or 60 min, resulted in an increase in GH secretion during a subsequent 60-min incubation period, both in the absence or in the presence of GRF (0·01–1 nmol/l). Pretreatment with GRF caused increased responsivity to GRF rather than significant sensitization of the GH response to GRF.
These observations demonstrate actions of SRIF, at low and probably physiological concentrations, which are more complex than those of a pure inhibitor of GH secretion. Pre-exposure of the pituitary to SRIF enhances subsequent GH secretion, suggesting that SRIF may play an additional physiological role in amplifying the GRF signal.
Journal of Endocrinology (1991) 128, 91–95
Control of progesterone and inhibin secretion during the luteal phase in the macaque
Authors: Smith K. B. , Fraser H. M. 
Published: December 2008

ABSTRACT
We investigated the temporal relationship between serum concentrations of progesterone and immuno-reactive inhibin after treatment with an LHRH antagonist ([N-Ac-d-Nal(2)1,d-pCl-Phe2,d-Trp3,d-hArg(Et2)6,d-Ala10]-LHRH), during the mid-luteal phase in the macaque. Further, in an attempt to obtain a model of transitory suppression of luteal function, the effect of treatment with the LHRH antagonist for 1, 2 or 3 days during the mid-luteal phase on serum concentrations of progesterone and immunoreactive inhibin was compared. Differences in the pattern of decline of the two hormones were observed. Progesterone concentrations fell by 6 h after antagonist administration while inhibin was not significantly suppressed until 48 h. Treatment with three injections of LHRH antagonist caused a sustained suppression of luteal function as shown by low serum concentrations of progesterone and inhibin. Recovery of progesterone and inhibin secretion was observed in two out of six macaques treated with two injections of antagonist and in three out of six treated with a single injection. Therefore, with the regimens of LHRH antagonist which we employed this approach was not conducive to obtaining a reliable transitory suppression of luteal function. To elucidate further the gonadotrophin control of inhibin, six macaques were treated with three injections of the LHRH antagonist to induce a permanent suppression of luteal function but received concomitantly either human chorionic gonadotrophin (hCG) or human FSH daily for 5 days (n = 3 per group). FSH failed to prevent the antagonist-induced fall in progesterone and inhibin while hCG treatment completely reversed the inhibitory effects of the LHRH antagonist. These results give further support to the concept that the secretion of inhibin, like progesterone, is integrated with the LH control of the corpus luteum. The slower decline in inhibin after LHRH antagonist suggests that the gonadotrophic stimulus to the corpus luteum results in a more prolonged stimulus for inhibin than for progesterone secretion, or that inhibin has a longer metabolic clearance rate.
Journal of Endocrinology (1991) 128, 107–113
Comparison of the luteolytic action of gonadotrophin-releasing hormone antagonist and cloprostenol, and the ability of human chorionic gonadotrophin and melatonin to override their luteolytic effects in the marmoset monkey
Authors: Webley G. E. , Hodges J. K. , Given A. , Hearn J. P. 
Published: December 2008

ABSTRACT
The effects of the luteolytic and luteotrophic agents cloprostenol, human chorionic gonadotrophin (hCG) and melatonin on the corpus luteum have been investigated in marmoset monkeys treated with an LHRH antagonist to reduce endogenous LH secretion. This has allowed the effects of these agents to be investigated in the absence of the principal endogenous luteotrophin.
Administration of the LHRH antagonist ([N-acetyl-dβNal1-d-pCl-Phe2-d-Phe3-d-Arg6-Phe7-Arg8-d-Ala10]NH2-LHRH) or cloprostenol between days 7 and 11 after ovulation (preimplantation) resulted in luteolysis. A significant (P<0·05) decrease in progesterone concentrations had occurred by 4 h after administration of the LHRH antagonist and was indeed preceded by a fall in LH concentrations. Coadministration of hCG with the LHRH antagonist prevented the fall in progesterone. In contrast, administration of cloprostenol resulted in an immediate fall in progesterone concentrations, to less than half the initial level within 1 h, and co-administration with hCG did not prevent the fall. Administration of hCG stimulated progesterone production when given 8 h after the LHRH antagonist but not after 24 h. Cloprostenol prevented the stimulation by hCG. Co-administration of melatonin with the LHRH antagonist did not prevent the decrease in progesterone concentrations. Melatonin was also not effective in preventing the fall in progesterone induced by cloprostenol. However, co-administration of melatonin and cloprostenol between days 17 and 21 after ovulation (post-implantation) significantly (P<0·05) delayed the fall in progesterone seen with cloprostenol alone.
These results suggest that while the LHRH antagonist and cloprostenol have different sites of action their effect is similar at the corpus luteum, that is in depriving the corpus luteum of luteotrophic support. The results also suggest that melatonin may be able to influence the luteolytic action of cloprostenol but that its effect varies with the stage of the cycle. The physiological role for such an action, if any, remains unknown.
Journal of Endocrinology (1991) 128, 121–129
Discordant levels of serum bioactive LH in man as measured in different in-vitro bioassay systems using rat and mouse interstitial cells and human granulosa-luteal cells
Authors: Ding Y.-Q. , Ranta T. , Nikkanen V. , Huhtaniemi I. 
Published: December 2008

ABSTRACT
Serum samples from healthy men (n = 6), perimenopausal women (n=9) and patients with polycystic ovarian disease (n = 4) were analysed for LH bioactivity by the two widely used in-vitro bioassay systems: the mouse and rat interstitial cell testosterone-formation assays. The results were compared with an assay employing LH-stimulated cyclic AMP production by cultured human granulosa-luteal cells. Average bioactive LH levels in the mouse cell assay were 1·6-fold higher than those measured using the rat assay. A good correlation (r = 0·89, P<0·01) was observed between the bioactive LH levels measured by these two assays. No significant difference was found between the sensitivities of the two assays: 0·009 ±0·003 IU/1 (mean ± s.e.m., n=10) with rat cells and 0·011±0·003 IU/1 (n=10) with mouse cells. The LH level resulting in half-maximal stimulation of testosterone production in the mouse model was twofold higher than that in the rat model (0·185 ±0.020 vs 0·083 ±0·022 IU/1, P<0·01). The bioactive LH levels measured by the human granulosa-luteal cell assay averaged 12% higher than those obtained with the rat assay (r =0·84, P<0·01), but 58% lower than levels measured with the mouse assay (r = 0·86, P<0·01). The data indicate that the target cell model used in the in-vitro bioassay of LH contributes to the documented discrepancies in reports on serum levels of bioactive LH. Although good correlations were found between all assay systems, the absolute levels of LH bioactivity measured with the rat assay are closer than mouse data to levels measured with a homologous bioassay employing human granulosa-luteal cells.
Journal of Endocrinology (1991) 128, 131–137
Characterization and localization of oxytocin receptors in the uterus and oviduct of the non-pregnant ewe using an iodinated receptor antagonist
Authors: Ayad V. J. , Guldenaar S. E. F. , Wathes D. C. 
Published: December 2008

ABSTRACT
Some of the binding characteristics of a novel oxytocin receptor ligand 125I-labelled [1-(β-mercapto-β, β-cyclopentamethylene propionic acid), 2-(ortho-methyl)-Tyr2,Thr4,Orn8,Tyr9-NH2]-vasotocin ([125I]OTA) have been determined in the sheep uterus. The compound was subsequently used for the autoradiographic localization of oxytocin receptors in the uterus and oviduct of the ewe.
Specific binding of [125I]OTA to crude membrane fractions of ovine endometrium was time-dependent and was unaffected by the addition of cations to incubation media. Endometrial membranes contained a single population of saturable, high-affinity binding sites for the iodinated ligand (dissociation constant (Kd) 0·23±0·08 nmol/l) and unlabelled oxytocin competed with [125I]OTA for binding sites with high affinity (Kd 1·29±0·4 nmol/l) in the presence of Mg2+ In contrast, unlabelled OTA was able to compete with high affinity (Kd 1·13±0·16 nmol/l) in the absence of cation. Competition studies with a number of oxytocin analogues and related peptides and the tissue distribution of [125I]OTA binding sites also indicated that [125I]OTA bound to the ovine oxytocin receptor. This was further validated by autoradiographic studies which showed specific labelling with [125I]OTA to be greater to uterus and oviduct obtained from ewes which had been killed within 2 days of oestrus than to similar tissue from ewes killed during the luteal phase. In both the ampullary and isthmic regions of the oviduct and the myometrium, [125I]OTA binding sites were confined to smooth muscle. Endometrial binding sites for [125I]OTA were consistently located on the luminal epithelium and epithelial cells lining secretory glands. In addition, in one ewe which had been killed 2 days after cloprostenol treatment, stromal cells were labelled in a caruncular region of the endometrium. The consistency of this observation between similar animals remains to be determined.
The autoradiographic technique demonstrated appears sufficiently sensitive to allow further studies into the distribution of the endometrial oxytocin receptor throughout the oestrous cycle, and into its regulation at luteolysis and during the establishment of pregnancy.
Journal of Endocrinology (1991) 128, 187–195
Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I), IGF-II and des(1–3)IGF-I in rats
Authors: Ballard F. J. , Knowles S. E. , Walton P. E. , Edson K. , Owens P. C. , Mohler M. A. , Ferraiolo B. L. 
Published: December 2008

ABSTRACT
Incubation of 125I-labelled insulin-like growth factor-I (IGF-I) with rat plasma at 4 °C led to the transfer of approximately half the radioactivity to 150 kDa and smaller complexes with IGF-binding proteins. The extent of association was greater with labelled IGF-II and essentially absent with the truncated IGF-I analogue, des(1–3)IGF-I. A greater degree of binding of IGF peptides with binding proteins occurred after i.v. injection of the tracers into rats, but most of the des(1–3)IGF-I radioactivity remained free. Measurement of the total plasma clearances showed the rapid removal of des(1–3)IGF-I compared with IGF-I and IGF-II; the mean clearances were 4·59, 1·20 and 1·34 ml/min per kg respectively. The mean steadystate volume of distribution was larger for des(1–3)IGF-I than for IGF-I and IGF-II (461, 167 and 181 ml/kg respectively), probably because of the differences in plasma protein binding. With all tracers, radioactivity appeared in the kidneys to a greater extent than in other organs. The amount of radioactivity found in the adrenals, brain, skin, stomach, duodenum, ileum plus jejunum and colon was in rank order, des(1–3)IGF-I > IGF-I > IGF-II. Since this ranking is the opposite of the abilities of the three IGF peptides to form complexes with plasma binding proteins, we propose that the plasma binding proteins inhibit the transfer of the growth factors to their tissue sites of action. Moreover, we suggest that IGF analogues that are cleared rapidly from blood may have greater biological potencies in vivo.
Journal of Endocrinology (1991) 128, 197–204
Effect of retinoids on protein kinase C activity and on the binding characteristics of the tri-iodothyronine nuclear receptor
Authors: Pailler-Rodde I. , Garcin H. , Higueret P. 
Published: December 2008

ABSTRACT
Retinoids and thyroid hormones exert profound effects on the development, growth and homeostasis of vertebrates. The receptor proteins which bind retinoic acid, tri-iodothyronine (T3) or steroid hormones and, as a result of this binding, interact with DNA to stimulate expression of specific genes, belong to the same recently discovered superfamily. The functionality of thyroid and steroid hormone receptors is thought to be related to a phosphorylation-dephosphorylation cycle. In the present work, the action of two retinoids (retinol and retinoic acid) was studied on the properties of T3-nuclear receptors and on protein kinase C (PKC) activity in the rat liver (PKC is known to be a phosphorylating enzyme for various proteins). The influence of 12-O-tetradecanoyl phorbol-13-acetate (TPA; known to enhance PKC activity) on the properties of T3-nuclear receptors was also investigated. Measurements of binding characteristics and enzyme activity were performed 4 or 12 h after a single i.p. injection of retinol or retinoic acid (6 mg/kg body weight) or 1 h after a single i.p. injection of TPA (0·7 mg/kg). The activity of PKC was increased 4 h after administration of the retinoids, and the affinity of the T3-nuclear receptor protein was increased markedly after 12 h. The activity of PKC and the affinity of the nuclear T3 receptor were both increased 1 h after administration of TPA. These observations provide indirect evidence that retinoids, particularly retinoic acid, induce an increase in PKC activity and a subsequent increase in the affinity of the T3-nuclear receptor protein.
Journal of Endocrinology (1991) 128, 245–251
Identification of a non-covalent oxytocin/neurophysin-I complex in the bovine ovary
Authors: Shukovski L. , Findlay J. K. , Smith A. I. 
Published: December 2008

ABSTRACT
Acid extracts of bovine preovulatory granulosa cells and corpora lutea (CL) were subjected to high-performance liquid chromatography (HPLC) and found to contain two peaks of immunoreactive (ir) oxytocin (OT), one corresponding to authentic OT and the second eluting 8 min later. The second peak was more abundant than authentic irOT in preovulatory follicles and in the early CL, but became less abundant as the CL matured (mid luteal) and was close to the limit of detection in the late CL. This peak could be detected only by an OT antiserum which recognized both the biologically active form of OT, as well as the post-translational processing intermediate Gly10-extended oxytocin. A second more specific OT antiserum (OT-933) did not recognize the second peak as strongly. Further analysis of the second peak revealed a complex of OT bound to its neurophysin (NP-I) which could be dissociated under denaturing conditions. Furthermore, we were able to create this complex in vitro by combining the two materials together under acid conditions, similar to the pH predicted in secretory granules, but not under neutral conditions. Measuring irNP-I by radioimmunoassay showed a single peak with a similar retention time to the OT/NP-I complex, confirming the identity of the unknown peak. Incubation of CL slices in culture showed a time-related release of both OT and NP-I, with OT having a greater rate of release in the mid luteal CL.
These data suggest the presence of an OT/NP-I complex in the bovine preovulatory granulosa cells and CL, as well as the unbound peptide presumably within the secretory granules. The ratio of OT/NP-I complex and free peptide changes with ageing of the the CL, perhaps indicating regulated differences in the post-translational processing of the prohormone.
Journal of Endocrinology (1991) 128, 305–314
Kallidin stimulates prolactin secretion from individual rat anterior pituitary cells
Authors: Stirland J. A. , Brown B. L. , Dobson P. R. M. 
Published: December 2008

ABSTRACT
Kinins are localized within the adenohypophysis where they have been shown to stimulate the release of pituitary hormones. In the present study we have investigated the effect of [Lys]-bradykinin (kallidin) on prolactin secretion at the single cell level from cultured male rat anterior pituitary cells. This was assessed by use of a reverse haemolytic plaque assay which permits quantitative evaluation of the proportion of all pituitary cells which are secreting prolactin, and the amount of prolactin secreted per lactotroph (plaque area). The rate of plaque development was used as an index of the rate of hormone secretion in time-course studies.
Kallidin induced a dose-dependent increase in both the percentage of plaque-forming cells and the median plaque area during the first 2 and 3 h of incubation respectively. The threshold concentration of kallidin was 10 nmol/l. After 4 h of kallidin stimulation there was no difference between treated and control mono-layers with respect to median plaque area and the total secretion index. Although recruitment of additional cells into the secretory pool cannot be excluded, this seems unlikely since at 3 and 4 h little or no difference was observed in the number of plaque-forming cells. The data suggest that initially kallidin accelerated the rate of prolactin secretion primarily by inducing an increase in the number of cells secreting prolactin, and subsequently by increasing the amount of hormone secreted per lactotroph. The results presented here are consistent with the proposed role of the kallikrein–kinin system in the paracrine or autocrine control of prolactin release from the pituitary gland.
Journal of Endocrinology (1991) 128, 315–320
Insulin binding to Leydig cells and insulin levels in testicular interstitial fluid at different stages of development in the rat
Authors: Grizard G. , Fournet M. , Rigaudière N. , Lombard-Vignon N. , Grizard J. 
Published: December 2008

ABSTRACT
Binding of insulin to purified intact Leydig cells (LC) and LC membranes, and levels of insulin in plasma and testicular interstitial fluid (IF) were quantitatively evaluated in rats at three stages of development. Specific insulin binding to intact LC increased significantly with age. Scatchard analysis of the binding data always gave curvilinear plots; the number of high affinity binding sites/LC were 2590±514, 3977±701 and 8342±2039 at 21, 40 and 70 days respectively. When the results were expressed per μg membrane protein, the maximal specific insulin binding also increased between 21 and 40 days but did not significantly change thereafter. With ageing, insulin levels in testicular IF decreased (3·05±0·30, 2·48±0·22 and 1·66±0·13 μg/l in 21-, 40- and 70-day-old rats) whereas plasma insulin increased. Taken together, these results suggest (1) that the intratesticular environment in this hormone cannot be evaluated by plasma insulin levels—testicular IF insulin concentration is probably a better index and (2) that insulin may play a role in the development of LC function during sexual maturation.
Journal of Endocrinology (1991) 128, 375–381
Evidence for the role of the secretory pattern of growth hormone in the regulation of serum concentrations of cholesterol and apolipoprotein E in rats
Authors: Oscarsson J. , Carlsson L. M. S. , Bick T. , Lidell A. , Olofsson S.-O. , Edén S. 
Published: December 2008

ABSTRACT
Adult male Sprague–Dawley rats were hypophysectomized and connected to an automatic i.v. infusion system. The same daily dose of human GH (hGH) was given either as eight daily pulses (3-h intervals) to mimic the male specific secretory pattern of GH or as a continuous infusion of GH, to mimic the female secretory pattern. Hypophysectomized rats received i.v. replacement therapy with l-thyroxine and cortisol. The rats were treated for 5 days. The serum cholesterol concentration was higher when hGH was given continuously than when hGH was given as eight daily pulses. The concentration of high-density lipoprotein (HDL)-cholesterol was not influenced by intermittent GH treatment, but increased when hGH was given as a continuous infusion. The serum concentration of apolipoprotein (Apo) E increased following treatment with a continuous infusion of hGH, whereas eight daily pulses of hGH had no effect. The serum concentration of ApoA-I was unaffected by hGH treatment. The serum concentration of ApoB decreased to the same degree whether hGH was given as a continuous infusion or as eight daily pulses. The serum concentration of triglycerides was not affected by hGH treatment.
These results indicate that the higher serum HDL-cholesterol and serum ApoE concentrations of female rats may be due to their more continuous secretion of GH. In contrast, the effects of GH on the serum concentration of ApoB, which is not sexually differentiated, may be independent of the mode of GH secretion.
Journal of Endocrinology (1991) 128, 433–438