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  • 1
    Electronic Resource
    Electronic Resource
    Prevention of Glucoprivic Stimulation of Corticosterone Secretion by Leptin Does Not Restore High Frequency Luteinizing Hormone Pulses in Rats (2001)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 13 (2001), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We have previously determined that exogenous leptin prevents the inhibition of pulsatile luteinizing hormone (LH) release in the fasting rodent. The present study tested the hypothesis that the mechanism by which leptin facilitates high LH secretion is through an attenuation of the stress response produced by a deficit in energy. Because hypogonadotropism is associated with activation of the hypothalamic-pituitary-adrenal (HPA) axis during both metabolic stress and nonmetabolic stress, our approach included a comparison of whether exogenous leptin could prevent the rise in corticosterone produced by a nonmetabolic stress (immobilization for 2 h), as well as by a widely used metabolic stress (transient glucoprivation by 2-deoxyglucose, 2DG; 400 mg/kg, b.w., i.v.). Each stressor was applied to well-fed ovariectomized rats (n = 4–6 per group), 2 h after leptin (3 µg/g, b.w., i.p.) or vehicle administration. Blood samples were collected through an indwelling atrial cannula every 6 min for 1 h before and for 2 h after the stress treatment to measure LH, leptin and corticosterone. During metabolic stress (acute glucoprivation), circulating leptin decreased, corticosterone increased and LH decreased; leptin administration abolished the increase in corticosterone, but pulsatile LH secretion remained inhibited. In contrast, during nonmetabolic stress (immobilization), leptin secretion was unaffected, but circulating corticosterone increased and LH decreased; leptin treatment did not prevent either the increase in corticosterone or the decrease in LH secretion. An important overall finding is that leptin can differentially alter the HPA axis depending upon the type of stress. In addition, whether the pattern of leptin is altered depends upon the type of stress. Although a glucoprivic-induced decrease in endogenous leptin can be a stressor responsible for the increase in corticosterone secretion, a nonmetabolic stress-induced increase in corticosterone is not mediated by leptin. Moreover, our results reveal that the depression of LH secretion when leptin is low during reduced energy availability is not due to activation of the HPA axis. During an energy deficit, exogenous leptin could not restore high frequency LH secretion when HPA function was restored to normal. Finally, the inability of leptin to increase LH secretion in the face of 2DG supports the notion that the action of leptin is dependent upon the degree of glucose availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2001.00638.x
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  • 2
    Electronic Resource
    Electronic Resource
    Intracerebroventricular Administration of Melanin-Concentrating Hormone Suppresses Pulsatile Luteinizing Hormone Release in the Female Rat (2000)
    Oxford, UK : Blackwell Science Ltd
    Journal of neuroendocrinology 12 (2000), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Melanin-concentrating hormone (MCH) has been reported to be involved in the regulation of feeding behaviour in rats and mice. Because many neuropeptides that influence ingestive behaviour also regulate reproductive function, the present study was designed to determine if central administration of MCH changes pulsatile secretion of luteinizing hormone (LH) in the rats. Wistar-Imamichi strain female rats were ovariectomized and implanted with oestradiol to produce a moderate inhibitory feedback effect on LH release. The effects of i.c.v. injections of MCH on LH release were examined in freely moving animals. Blood samples were collected every 6 min for 3 h through an indwelling cannula. After 1 h of sampling, MCH (0.1, 1 or 10 μg/animal) or vehicle (saline) was injected into the third cerebroventricle. Because MCH is also reported to affect the hypothalamo-pituitary-adrenal (HPA) axis, which in turn, can influence reproductive function, plasma corticosterone concentrations were determined in the same animals at 30-min intervals during the first and last hours and every 12 min during the second hour of the 3-h sampling period. When expressed as per cent changes, mean plasma LH concentrations after MCH administration were significantly lower in the animals injected with all doses of the peptide compared with vehicle-treated animals; LH pulse frequency was significantly lowered by 1 μg of MCH. Per cent changes in mean plasma corticosterone levels were not significantly affected by MCH administration. These results in oestradiol-treated ovariectomized rats indicate that central MCH is capable of inhibiting pulsatile LH secretion. We have previously shown that 48-h fasting suppresses pulsatile LH release in the presence of oestrogen. Take together, these results raise the possibility that MCH could play a role in mediating the suppression of LH secretion during periods of reduced nutrition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2000.00482.x
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  • 3
    Electronic Resource
    Electronic Resource
    Pineal melatonin rhythms and the timing of puberty in mammals (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 946-954 
    Details
    ISSN: 1420-9071
    Keywords: Puberty ; photoperiod ; pineal ; melatonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The direction of change in daylength provides the seasonal time cue for the timing of puberty in many mammalian species. The pattern of melatonin secretion from the pineal gland transduces the environmental light-dark cycle into a signal influencing the neuroendocrine control of sexual maturation. The change in duration of nocturnal melatonin secretion is probably the key feature of the melatonin signal which conveys daylength information. This information may also be used by neuroendocrine axes controlling seasonal changes in pelage colour, growth and metabolism. The mechanism of action of melatonin on neuroendocrine pathways is unknow. Although the ability to synthesize and secrete melatonin in a pattern that reflects the duration of the night may not occur until the postnatal period, the rodent and ovine foetus has the ability to respond in utero to photoperiodic cues to which its mother is exposed in late gestation. Transplacental passage of maternal melatonin is likely to be the mechanism by which photoperiodic cues reach the foetus. Species which do not exhibit seasonal patterns of puberty, such as the human, also secrete melatonin in a pattern which reflects the environmental light-dark cycle, but they do not respond reproductively to the seasonal melatonin information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01953052
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  • 4
    Electronic Resource
    Electronic Resource
    Tissue-Specific Fatty Acid Composition of Glandular Trichomes of Mite-Resistant and -Susceptible Pelargonium xhortorum (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 955-968 
    Details
    ISSN: 1573-1561
    Keywords: Fatty acids ; geraniums ; glandular trichomes ; glycolipids ; Pelargonium xhortorum ; phospholipids ; ω5-unsaturated fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Anacardic acids, alkyl phenolic acids excreted by tall glandular trichomes of the garden geranium, Pelargonium xhortorum, confer small-pest resistance. Up to 90% of the trichome exudate from mite-resistant P. xhortorum inbreds consists of an unusual anacardic acid with an unsaturated omega-5 (ω5) alkyl chain. As fatty acids are biochemical precursors to anacardic acids, we examined by GC the fatty acid composition of leaves, pedicels, petals, sepals, mature seeds, and glandular trichomes from pest-resistant and pest-susceptible Pelargonium inbred lines to determine the localization of ω5-fatty acids within plant tissues. The fatty acid composition of lipid classes (galactolipids, phospholipids, and neutral lipids) extracted from glandular trichomes from mite-resistant pedicels were also examined. ω5-Fatty acids (16:1Δ11 and 18:1Δ13) were found only in the glandular trichomes from pest-resistant geraniums (27.2% in trichomes of pedicels) and were localized predominantly in the phospho- and galactolipids (phosphatidylinositol, 25.9%; phosphatidylcholine, 18.2%; monogalactosyldiglyceride, 15.5%; and diglactosyldiglyceride, 14.0%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020865322035
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  • 5
    Electronic Resource
    Electronic Resource
    Melatonin and puberty in female lambs exposed to EMF: A replicate study (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 16 (1995), S. 119-123 
    Details
    ISSN: 0197-8462
    Keywords: EMF ; melatonin ; puberty ; sheep ; transmission line ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: In an earlier study, we found no effects of 60 Hz electric and magnetic fields (EMF) from a 500 kV transmission line on serum melatonin patterns or on puberty in ten female Suffolk lambs (Ovis aries). We conducted a larger replicate study of 15 lambs exposed to a mean electric field of 6.3 kV/m and a mean magnetic field of 3.77 μT and 15 controls exposed to EMF two orders of magnitude weaker than in the line area. The replicate produced essentially the same results as our previous study. © 1995 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250160208
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