Plasma Orexin-A Levels Do Not Undergo Circadian Rhythm in Young Healthy Male Subjects.

Orexin-A (OXA) has been originally isolated from a precursor peptide prepro-orexin from the lateral hypothalamus. The orexin system has been attributed to important functions in sleep, arousal and regulation of energy homeostasis. In addition to its high levels in cerebrospinal fluid, OXA is present in blood.

Effects of hypoxia and reoxygenation on the antioxidant defense system of the locomotor muscle of the crab Neohelice granulata (Decapoda, Varunidae).

Crustaceans often occur in areas with variations in oxygen and experience situations known as hypoxia and reoxygenation. Consequences of such situations are increased levels of reactive oxygen species. To avoid oxidative damage intertidal crabs appear to possess an efficient antioxidant defense system (ADS).

Transcranial bright light exposure via ear canals does not suppress nocturnal melatonin in healthy adults--a single-blind, sham-controlled, crossover trial.

We investigated whether transcranial bright light (TBL) affects nocturnal melatonin and cortisol secretion in sham-controlled crossover trial. Young healthy adults were exposed in random order to 24 minutes of TBL or sham exposure via ear canals at 01:10 h. Saliva and urine samples were collected hourly between 21 h-03 h and 06 h-09 h.

The effect of hormone therapy on serum melatonin concentrations in premenopausal and postmenopausal women: a randomized, double-blind, placebo-controlled study.

Objectives: Melatonin levels decrease physiologically with age, and possibly with the transition to menopause. The plausible influence of hormone therapy (HT) on melatonin is poorly understood. The aim of this randomized, placebo-controlled, double-blind trial was to investigate the effect of HT administration on serum melatonin concentrations in late premenopausal and postmenopausal women.

Melatonin in perimenopausal and postmenopausal women: associations with mood, sleep, climacteric symptoms, and quality of life.

Objective: Melatonin synthesis and secretion are partly modulated by estrogen and progesterone. Changes in melatonin concentrations, possibly related to the menopausal transition, may be associated with climacteric mood, sleep, and vasomotor symptoms. The aims of this study were to compare the serum concentrations of melatonin in perimenopausal and postmenopausal women and to evaluate melatonin's influence on mood, sleep, vasomotor symptoms, and quality of life.

Effects of melatonin in connection with the antioxidant defense system in the gills of the estuarine crab Neohelice granulata.

Numerous studies have shown that melatonin exerts some influence on the antioxidant defense system (ADS) in vertebrates, but for crustaceans no such effect has been demonstrated till now. However, earlier reports did show a similar profile of daily variations in the ADS of the gills and the melatonin content of the eyestalk in the crab Neohelice granulata and, thus, the aim of this study was to take a closer look at the effects of melatonin in the gill ADS of N. granulata.

Long-term postinfarction melatonin administration alters the expression of DHPR, RyR2, SERCA2, and MT2 and elevates the ANP level in the rat left ventricle.

We investigated the effect of 2 wk continuous postinfarction subcutaneous melatonin supply on the expression of the rat left ventricular (LV) dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum Ca(2+)-ATPase2 (SERCA2), as they are fundamental proteins in cardiac contractility. The levels of plasma and LV atrial (ANP) and brain natriuretic peptide and melatonin were also measured, as was the expression of LV MT(1) and MT(2) receptors and pineal arylalkylamine N-acetyltransferase. Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery and vehicle or melatonin (4.

Daily variation of melatonin content in the optic lobes of the crab Neohelice granulata.

Melatonin is a biogenic amine, known from almost all phyla of living organisms. In vertebrates melatonin is produced rhythmically in the pinealocytes of the pineal gland, relaying information of the environmental light/dark cycle to the organism. With regard to crustaceans only a handful of studies exist that has attempted to identify the presence and possible daily variation of this substance.

The effect of myocardial infarction on the synthesis, concentration and receptor expression of endogenous melatonin.

We examined the time course of changes in the synthesis and levels of endogenous melatonin and in the expression of MT(1) and MT(2) melatonin receptors 1 day, 2 and 4 wk after myocardial infarction (MI) in rats. MI was produced by ligation of the left anterior descending coronary artery. Transthoracic echocardiography was performed to characterize structural and functional changes after MI.

Urinary melatonin: a noninvasive method to follow human pineal function as studied in three experimental conditions.

The aim of this study was to examine whether urinary melatonin, rather than urinary 6-sulfatoxymelatonin (aMT6s), can be used as an indicator of diurnally and seasonally changing melatonin secretion. The subjects (n=15) spent three separate 24-hr periods in a climatic chamber during winter (n=7) and summer (n=8). Blood and urine samples were obtained during each period at 2- to 5-hr intervals.

The expression of MT1 and MT2 melatonin receptor mRNA in several rat tissues.

The mechanisms that mediate the various effects of melatonin in mammalian tissues are not always known. Therefore, the aim of this study was to investigate whether MT(1) and MT(2) melatonin receptors are expressed in certain tissues of the rat. The expression of MT(1) and MT(2) melatonin receptor mRNA was determined using a real-time quantitative RT-PCR method.

Endogenous ouabain-like factor (OLF) secretion is modulated by nicotinic mechanisms in rat adrenocortical cells.

This study tested the hypothesis that rat adrenocortical secretion of endogenous ouabain-like factor (OLF) is regulated by nicotinic mechanisms. OLF secreted by dispersed cell suspensions of zona glomerulosa (ZG) and fasciculata/reticularis (ZFR) cells was found to co-elute with authentic ouabain by reverse phase HPLC; OLF concentrations in cell supernatants were measured by radioimmunoassay. Nicotine (10(-6) - 10(-3) M) stimulated significant OLF secretion in rat adrenocortical cells.

Changes in plasma concentrations of immunoreactive ouabain in the tilapia in response to changing salinity: is ouabain a hormone in fish?

Ouabain, a cardiac glycoside and inhibitor of Na(+), K(+)-ATPase, is now believed to be a steroid hormone in mammals, involved in blood pressure and volume regulation and possibly acting as a natriuretic hormone. We have identified ouabain-like immunoreactivity in the plasma and tissues of a euryhaline teleost, the tilapia (Oreochromis mossambicus), by means of solid-phase extraction followed by a specific radioimmunoassay. Plasma concentrations of immunoreactive ouabain were 5-20pg/ml.

Elevated blood levels of endogenous ouabain-like factor in preterm versus mature newborns at birth.

Compared to healthy adults, elevated levels of endogenous ouabain-like factor (OLF) have already been shown in the cord blood, and a role of OLF in the maintenance of high Na(+) excretion by reducing tubular sodium reabsorption during intrauterine life was suggested. In this study, we aimed to measure OLF cord blood levels of premature and mature newborns to provide further data on the possible physiological significance of this compound in neonates. OLF was assessed in the cord blood of newborns (28-41 weeks) and in the blood of healthy adults using ouabain radioimmunoassay.

Induction of melatonin synthesis in Tetrahymena pyriformis by hormonal imprinting--a unicellular "factory" of the indoleamine.

Melatonin is present in Tetrahymena and its synthesis can be enhanced by pretreatment (imprinting) with melatonin. Two days after imprinting melatonin level is elevated in the cells and more elevated in the supematant. Such a minute quantity, as 10(-12) M melatonin for 1 hour is able to provoke imprinting, however the effect is more expressed using 10(-6) M.

Important amino acids for the function of the human MT1 melatonin receptor.

Models of G protein-coupled melatonin receptor structure suggest that ligand recognition occurs in a binding pocket formed by transmembrane helices III, V and VII. Constitutively active mutations in G protein-coupled receptors have revealed that transmembrane helix III/intracellular loop 2 interface and transmembrane domain VI are critical regions in receptor activation. In this study, nine site-directed mutants of the human MT1 melatonin receptor were created to test the importance of specific amino acids in these regions in ligand recognition and receptor activation events.

Effect of controlled-release melatonin on sleep quality, mood, and quality of life in subjects with seasonal or weather-associated changes in mood and behaviour.

This study aimed to explore the effects of melatonin on sleep, waking up and well being in subjects with varying degrees of seasonal or weather-associated changes in mood and behaviour. Fifty-eight healthy adults exhibiting subsyndromal seasonal affective disorder (s-SAD) and/or the negative or positive type of weather-associated syndrome (WAS) were randomised to either 2 mg of sustained-release melatonin or placebo tablets 1-2 h before a desired bedtime for 3 weeks. Outcome measures were changes from baseline in sleep quality, sleepiness after waking, atypical depressive symptoms and health-related quality of life by week three.

Melatonin in the unicellular Tetrahymena pyriformis: effects of different lighting conditions.

Melatonin content in the cellular fraction and medium of Tetrahymena pyriformis GL cultures was measured at different time points of light and dark exposures. Tetrahymena produced, stored and secreted immunoreactive melatonin, which in displacement and HPLC studies, behaved like synthetic melatonin. There was not a continuous secretion of melatonin produced by the cells.

The influence of anaesthesia and surgery on the circadian rhythm of melatonin.

Background: Operations are typically associated with sleep and other circadian rhythm disturbances. The present study was set up to evaluate the influence of spinal and general anaesthesia associated with knee surgery on the circadian rhythm of melatonin, which has sleep inducing properties. Previously this context has been studied only in some invasive operations and it might be that general anaesthesia induces more disturbances on circadian rhythm of melatonin than operations done with patients awake.

Radioiodinated tyrosyl-ouabain and measurement of a circulating ouabain-like compound.

Background: Assays for endogenous ouabain, a cardiac glycoside believed to be involved in blood pressure and volume regulation, are characterized by laboratory-specific plasma values that are measured by different assays. Because of this variability, our study focused on the development of a new (125)I-labeled ouabain derivative for RIA of high sensitivity.

Methods: We generated rabbit antisera against a ouabain-thyroglobulin conjugate.

2,3,7,8-Tetrachlorodibenzo-p-dioxin alters melatonin metabolism in fish hepatocytes.

Pineal hormone melatonin is an important regulator of endocrine and circadian rhythms in vertebrates. Since liver is assumed to be the major organ in the metabolism of this indole hormone, we investigated the effect of the known Ah-receptor agonist, 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) on melatonin metabolism in fish hepatocytes as well as the in vitro effect of melatonin on trout hepatic microsomal cytochrome P4501A (CYP1A) catalyst. Primary cell cultures of rainbow trout hepatocytes were exposed to [3H]melatonin (1 nM to 1 microM) alone and in combination with TCDD (50 pM) at 15 degrees C for 24 or 48 h.

Radioimmunoassay of plasma ouabain in healthy and pregnant individuals.

Ouabain was recently isolated from human plasma, bovine hypothalamus and bovine adrenal in attempts to identify endogenous substances inhibiting the cell membrane sodium pump. A number of radioimmunoassays have been developed in order to study the clinical significance of ouabain. The results have been controversial with regard to the presence and chemical nature of plasma ouabain-like immunoreactivity.

Suppression of melatonin secretion by bright light in seasonal affective disorder.

Eleven patients with winter seasonal affective disorder and 10 healthy controls were exposed to light of 3300 lux for 5 min and for 1 hour respectively on consecutive evenings at 22:00 hours during winter and summer. In the winter, the measurements were undertaken both before and after the treatment with bright light for 2 weeks. In the summer, there was no treatment.

Decrease in melatonin precedes follicle-stimulating hormone increase during perimenopause.

Melatonin, the hormone of the pineal gland, which in animal studies has been found to inhibit aging processes, is secreted in smaller amounts towards senescence. Menopause, an aging process in women, is known to be associated with typical changes in gonadotropin and sex steroid secretion. Our main objective was to study the possible role of melatonin in the hormonal regulation of menopause.