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  • 1
    Electronic Resource
    Electronic Resource
    Effects of N-Methyl-D,L-Aspartate on Beta-Endorphin and Prolactin Secretion in Rams Exposed to Long or Short Days (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 3 (1991), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In a previous study we demonstrated that the injection of the excitatory amino-acid N-methyl-D, L-aspartate (NMDA) stimulates an acute increase in the peripheral blood concentrations of luteinizing hormone in Soay rams, and this response varies with the photoperiodically-induced reproductive cycle. To extend these observations, we have now measured the changes in the blood concentrations of β-endorphin and prolactin in the same animals to establish whether NMDA stimulates the secretion of other pituitary hormones. Groups of adult Soay rams were exposed to alternating 16-weekly periods of long and short days to induce a long-term cycle in the endogenous secretion of β-endorphin (maximum under short days) and prolactin (maximum under long days). NMDA injected intravenously caused a dose-dependent increase in the blood plasma concentrations of β-endorphin (over the range 1 to 20 mg/kg NMDA). The initial increase in β-endorphin occurred within 2 to 4 min with peak levels after 20 to 100 min. The magnitude of the β-endorphin response was greatest following exposure to long days when the endogenous secretion of β-endorphin was low, while the duration of the response was greatest following exposure to short days when the endogenous secretion of β-endorphin was high. NMDA injected intravenously also caused a dose-dependent increase in the blood plasma concentrations of prolactin but this only occurred following exposure to long days when the endogenous secretion of prolactin was high. At this time the initial increase in prolactin concentrations occurred within 2 to 4 min after the injection of NMDA as for β-endorphin but the values continued to increase for 2 to 4 h. In a separate experiment, it was shown that pretreatment of the rams with dexamethasone (synthetic glucocorticoid, 133.4 μg/kg iv) blocked the β-endorphin response to NMDA but had no effect on the prolactin response. This indicates that NMDA stimulates the secretion of β-endorphin from the corticotrophs probably acting centrally to induce the release of corticotrophin-releasing hormone and/or arginine vasopressin, while NMDA acts through separate mechanisms to affect the secretion of prolactin.The overall results show that NMDA can be used as a probe to investigate the neuroendocrine control of β-endorphin and prolactin in addition to luteinizing hormone as described previously. The multiple responses are likely to represent the effects of NMDA acting on the hypothalamus to induce the acute release of peptides and other hormones into the pituitary portal blood system to affect the corticotrophs, lactotrophs and gonadotrophs. The variation in responsiveness to NMDA related to the photoperiodic cycle may reflect changes in the synthesis and storage of the hypothalamic hormones and the influence of other neural systems. Alternatively, the changes in the secretion of endogenous excitatory amino-acids and NMDA receptors may constitute part of the neuroendocrine mechanism relaying the effects of photoperiod.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1991.tb00307.x
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  • 2
    Electronic Resource
    Electronic Resource
    Luteinizing Hormone Responses to N-Methyl-D,L-Aspartate During a Photoperiodically-lnduced Reproductive Cycle in the Ram (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 3 (1991), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Aspartate and glutamate represent a major class of excitatory amino-acid neurotransmitters in the vertebrate brain, and stimulation of gtutaminergic receptors by the specific agonist N-methyl-D, L-aspartate (NMDA) induces luteinizing hormone-releasing hormone (LHRH) and LH secretion. In this study, we used NMDA as a probe to investigate the hypothalamic regulation of LH secretion at different stages of a reproductive cycle in Soay rams induced by exposure to alternating 16-week periods of long and short days. NMDA (20 mg/kg) injected intravenously caused an acute increase in blood plasma concentrations of LH, with a significant increase within 2 to 4 min, and peak levels within 20 min. The magnitude of the response changed markedly during the cycle; it was greatest in the sexually inactive phase under long days (with a linear dose-response over the range 1 to 20 mg/kg NMDA) and least in the sexually active phase under short days (only 20 mg/kg NMDA produced a small response). Pituitary responsiveness to a standard dose of LHRH (5.3 ng/kg iv) varied only slightly at the different stages and could not account for the observed changes in the LH response to NMDA. There were the expected changes in the endogenous pattern of LH secretion during the cycle, with high frequency LH pulses occurring during the sexually active phase. There was an inverse relationship between the frequency of LH pulses and the LH response to NMDA. Pretreatment of rams with an LHRH antagonist (36 μg/kg iv; Syntex, RS18286) totally blocked the LH response to both NMDA and LHRH, while in a separate study, treatment with dexamethasone (synthetic glucocorticoid, 133.4 μg/kg iv) partially blocked the LH responses. The overall results indicate that NMDA stimulates LHRH secretion in the ram and the response is independent of the activation of the hypothalamo-pituitary-adrenal axis. The variation in the LH response during the reproductive cycle may reflect changes in the releasable stores of LHRH in the median eminence. These appear to be depleted in the sexually active phase, when LHRH is secreted in pulses at high frequency. The variation in the response to NMDA may also reflect changes in release of endogenous excitatory amino-acids, which act via NMDA receptors to form part of the physiological regulation of the reproductive cycle in the ram.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1991.tb00280.x
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  • 3
    Electronic Resource
    Electronic Resource
    N-Methyl-DL-Aspartate Receptor Antagonism by D-2-Amino-5-Phosphonovaleric Acid Delays Onset of Puberty in the Female Rat (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 2 (1990), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: To investigate the possible role of N-methyl-DL-aspartate (NMDA) receptor activation in the initiation of puberty, we examined the effects of the selective competitive antagonist 2-amino-5-phosphonovaleric acid (AP5) on the timing of vaginal opening. Paired and weight-matched litter mates of immature female rats were implanted with osmotic minipumps for the intracerebroventricular infusion of DL- or D-AP5 or artificial cerebrospinal fluid from 27 to 30 days of age for 14 days. Each animal was weighed and examined daily for vaginal opening as the indicator of first oestrous. Infusion of 20 or 40 mM DL-AP5 beginning on Day 30 failed to delay vaginal opening. Administration 50mM of the single enantiomer D-AP5 beginning on Day 27 significantly delayed the age of vaginal opening to 40.6±1.1 (mean ± SEM) days compared to the cerebrospinal fluid-infused controls (36.5 ± 0.6 days). Blockade of NMDA receptors in the D-AP5-treated animals was confirmed on Day 32 by the suppression of luteinizing hormone response to intravenous NMDA (20 mg/kg) while the response to exogenous luteinizing hormone-releasing hormone (50 ng/kg) remained intact. AP5-treated animals had a slower rate of growth (3.1 ± 0.2 g/day) compared to controls (4.2 ± 0.2 g/day). However, a similar degree of growth retardation produced by a 75% restricted diet in untreated juvenile animals did not delay vaginal opening. This suggests that the slower growth rate in the D-AP5-treated animals could not account for the delayed onset of puberty. In conclusion, these data suggest that blockade of central NMDA receptors inhibits excitatory mechanisms which may be important in the control of pubertal onset in the female rat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1990.tb00457.x
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  • 4
    Electronic Resource
    Electronic Resource
    The crystallization and phase transformation of stabilizer-doped zirconia powders with H"2SO"4 additive
    Amsterdam : Elsevier
    Journal of Crystal Growth 96 (1989), S. 96-100 
    Details
    ISSN: 0022-0248
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-0248(89)90278-9
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  • 5
    Electronic Resource
    Electronic Resource
    Phospholipase A2 catalyses in organic media
    Amsterdam : Elsevier
    Tetrahedron Letters 34 (1993), S. 1959-1962 
    Details
    ISSN: 0040-4039
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0040-4039(00)91974-9
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  • 6
    Electronic Resource
    Electronic Resource
    Higher-order approximation techniques for estimating stochastic parameter of a sediment transport model (1998)
    Springer
    Stochastic environmental research and risk assessment 12 (1998), S. 359-375 
    Details
    ISSN: 1436-3259
    Keywords: Key words: Non-homogeneous Poisson model ; parameter estimation ; approximation technique ; Taylor series ; cumulative probability distribution function ; intensity function ; error analysis.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract: Higher-order approximation techniques for estimating stochastic parameter of the non-homogeneous Poisson (NHP) model are presented. The NHP model is characterized by a two-parameter cumulative probability distribution function (CDF) of sediment displacement. Those two parameters are the temporal and spatial intensity functions, physically representing the inverse of the average rest period and step length of sediment particles, respectively. Difficulty of estimating the parameters has, however, restricted the applications of the NHP model. The approximation techniques are proposed to address such problem. The basic idea of the method is to approximate a model involving stochastic parameters by Taylor series expansion. The expansion preserves certain higher-order terms of interest. Using the experimental (laboratory or field) data, one can determine the model parameters through a system of equations that are simplified by the approximation technique. The parameters so determined are used to predict the cumulative distribution of sediment displacement. The second-order approximation leads to a significant reduction of the CDF error (of the order of 47%) compared to the first-order approximation. Error analysis is performed to evaluate the accuracy of the first- and second-order approximations with respect to the experimental data. The higher-order approximations provide better estimations of the sediment transport and deposition that are critical factors for such environment as spawning gravel-bed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004770050025
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  • 7
    Electronic Resource
    Electronic Resource
    The prevalence of diabetic impotence (1980)
    Springer
    Diabetologia 18 (1980), S. 279-283 
    Details
    ISSN: 1432-0428
    Keywords: Diabetic impotence ; prevalence ; aetiological factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In a survey of 541 diabetic males, aged 20–59 years, 190 (35%) had erectile impotence. Using linear logistic regression models for analysis the five most significant associations with impotence were age (p〈0.001), treatment with either insulin or oral hypoglycaemic agents (p〈0.001), retinopathy (p〈0.001), symptomatic peripheral neuropathy (p〈0.001) and symptomatic autonomic neuropathy (p〈0.005). The greatest correlations were found in patients with severe microangiopathy, as demonstrated by proliferative retinopathy and symptomatic autonomic neuropathy. In addition the duration of diabetes and the presence of ischaemic heart disease, nephropathy and poor diabetic control may also be associated with diabetic impotence. It is concluded that diabetic impotence is still a common problem and may have a multifactorial aetiology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251005
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  • 8
    Electronic Resource
    Electronic Resource
    Geochemistry of HCO3 − at the sediment-water interface of lakes from the Southwestern Chinese plateau (1997)
    Springer
    Water, air & soil pollution 99 (1997), S. 381-389 
    Details
    ISSN: 1573-2932
    Keywords: diffusion ; alkalinity ; sediment-water interface ; southwestern Chinese plateau ; carbonates ; carbon isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Sediments were cored, and the sediment-water interface and overlying waters were sampled in 5 lakes from the southwestern Chinese plateau during 1991-95. The geochemistry of HCO3 − at the sediment-water interface was examined by studying detailed profiles of pH, HCO3 − concentrations and 813C of dissolved inorganic carbon (DIC) in overlying lake water and porcwater near the sediment-water interface. Dissolution-precipitation equilibrium of carbonates, diffusion flux, and the extent of the influence of diffusion on the whole lake were calculated. The results show that the HCO3 − near the interface carried isotopic characteristics of decomposition of organic matter during early diagenesis, and that the porcwater in surface sediments was unsaturated relative to calcite, and gradually saturated with depth. Furthermore, the interface is a source of HCO3 to the overlying water. Alkalinity (Alk) diffusion flux from sediments to the overlying water due to concentration gradients ranged front 0.51 to 24.33 × 104 mol cm−2 a−1. The calculated contribution of the diffusion of Alk to the overlying water ranged from 0.46% to 49.42%. Diffusion is an important source of Alk in lakes with a long residence time and a relatively shallow depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02406878
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  • 9
    Electronic Resource
    Electronic Resource
    Changes in erectile responsiveness during androgen replacement therapy (1983)
    Springer
    Archives of sexual behavior 12 (1983), S. 59-66 
    Details
    ISSN: 1573-2800
    Keywords: male sexuality ; erection ; androgen ; hypogonadal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Psychology
    Notes: Abstract Erections in response to erotic films and fantasies were measured in eight hypogonadal men, with and without androgen replacement, and eight age-matched controls. Erections to films in the hypogonadal men did not differ from those of the controls and were not affected by androgen replacement. Erections to fantasy were significantly smaller and slower to develop in the hypogonadal men and did show significant improvement during androgen replacement. These preliminary results suggest that erections to certain types of stimuli are relatively independent of androgens, whereas the response to fantasy may be androgen dependent. The implications of these findings are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01542116
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