Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Der Hautarzt 50 (1999), S. 5-11 
    ISSN: 1432-1173
    Keywords: Schlüsselwörter Melatonin (N-Acetyl-5-Methoxytryptamin) ; Zirkadianer Rhythmus ; Schlaf-Wach-Rhythmus ; Radikalfänger ; Key words Melatonin (N-acethyl-5-methoxytryptamin) ; Circadian rhythm ; Daily sleep induction ; ageing ; Free radical scavenger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Melatonin (N-acetyl-5-methoxytryptamine) is a hormone with multiple functions in humans, produced by the pineal gland and stimulated by β-adrenergic receptors. Serum melatonin levels exhibit a circadian rhythm with low levels during the day, rise in the evening and maximum levels at night between 2 and 4 a.m.. Melatonin participates in the regulation of several physiological processes such as seasonal biological rhythm, daily sleep induction, aging and modulation of immunobiological defence reactions. Furthermore, melatonin has a highly lipophilic molecular structure facilitating penetration of cell membranes and serving as an extra- and intracellular free radical scavenger. Melatonin seems to quench mainly hydroxyl radicals, the most damaging of all free radicals. Melatonin may play a role in the etiology and treatment of several dermatoses e.g. atopic eczema, psoriasis and malignant melanoma. The influence of melatonin on hair growth is another aspect. Topical application of melatonin inhibits the development of UV-erythema. Penetration through skin after topical application and oral bioavailability auxit further investigations on the pharmacokinetic and pharmacodynamic actions of melatonin.
    Notes: Zusammenfassung Melatonin (N-Acetyl-5-Methoxytryptamin) ist ein unter dem Einflußβ-adrenerger Rezeptoren von der Glandula pinealis produziertes und sezerniertes Hormon mit vielfältigem Wirkungsspektrum. Die Ausschüttung des Hormons folgt einem zirkadianen Rhythmus mit niedrigen, gleichmäßigen Spiegeln tagsüber und einem abendlichen Ansteigen und nächtlichen Peak zwischen 2.00 und 4.00 Uhr. Melatonin beeinflußt den saisonalen Biorhythmus, den Schlaf-Wach-Rhythmus, den Alterungsprozeß und moduliert immunbiologische Abwehrfunktionen. Zusätzlich besitzt Melatonin unabhängig von einem Rezeptorsystem durch seine starken lipophilen Eigenschaften die Fähigkeit, frei durch Zellmembranen zu diffundieren und im extra- wie intrazellulären Raum als Radikalfänger zu wirken. Die Affinität zu dem stark schädigenden Hydroxylradikal ist besonders groß. In der Dermatologie ergeben sich für Melatonin Perspektiven bei einigen Hauterkrankungen wie zum Beispiel dem atopischen Ekzem, der Psoriasis und dem malignen Melanom. Der Einfluß von Melatonin auf das Haarwachstum ist ein weiterer Aspekt. In topischer Anwendung hat Melatonin eine suppressive Wirkung auf die Ausbildung eines UV-Erythems. Über die Penetrationseigenschaften durch die Haut und die orale Verfügbarkeit liegen einige Erkenntnisse vor, die durch weitere Untersuchungen der Pharmakokinetik und Pharmakodynamik ergänzt werden können.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-0819
    Keywords: Key words Hydrothermal system ; Fluid geochemistry ; Stable isotopes ; Geochemical monitoring ; Taal Volcano
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic Main Crater Lake (pH〈3) lying in the center of an active vent complex, which is surrounded by a slightly alkaline caldera lake (Lake Taal). This peculiar situation makes Taal prone to frequent, and sometimes catastrophic, hydrovolcanic eruptions. Fumaroles, hot springs, and lake waters were sampled in 1991, 1992, and 1995 in order to develop a geochemical model for the hydrothermal system. The low-temperature fumarole compositions indicate strong interaction of magmatic vapors with the hydrothermal system under relatively oxidizing conditions. The thermal waters consist of highly, moderately, and weakly mineralized solutions, but none of them corresponds to either water–rock equilibrium or rock dissolution. The concentrated discharges have high Na contents (〉3500 mg/kg) and low SO4/Cl ratios (〈0.3). The Br/Cl ratio of most samples suggests incorporation of seawater into the hydrothermal system. Water and dissolved sulfate isotopic compositions reveal that the Main Crater Lake and spring discharges are derived from a deep parent fluid (T≈300  °C), which is a mixture of seawater, volcanic water, and Lake Taal water. The volcanic end member is probably produced in the magmatic-hydrothermal environment during absorption of high-temperature gases into groundwater. Boiling and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges. Incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the lakes and by the fact that Lake Taal was directly connected to the China sea until the sixteenth century. The depth to the seawater-meteoric water interface is calculated to be 80 and 160 m for the Main Crater Lake and Lake Taal, respectively. Additional data are required to infer the hydrologic structure of Taal. Geochemical surveillance of the Main Crater Lake using the SO4/Cl, Na/K, or Mg/Cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...