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Melatonin enhances cortisol levels in aged but not young women.
No full textIn spite of animal data showing an effect of melatonin in the regulation of the hypothalamus-pituitary-adrenal (HPA) axis, no effect of melatonin on cortisol has been evidenced in young men. Gender and aging are believed to influence the regulation of the HPA axis, and may thus modulate the melatonin effect on cortisol. In this study we investigated whether an effect of melatonin on cortisol can be observed in women of different age. Six young women in early follicular phase (22-32 years; EFW) and eight aged women in postmenopause (54-62 years; PMW) were studied. At 08.00 h on two consecutive days each woman received, randomly and in double-blind fashion, a pill of placebo or melatonin (100 mg). Serum levels of melatonin and cortisol were evaluated at 20-min intervals for 48 h. In comparison to EFW, PMW showed an earlier onset of nocturnal melatonin (p < 0.05) and cortisol rise (p < 0.01) and higher cortisol levels at lunch (p < 0.05) and early evening (p < 0.01). Melatonin administration did not modify serum cortisol levels in EFW but elicited a marked increase of daytime cortisol levels in PMW (p < 0.02). The present data reveal that in aged PMW the cortisol levels are enhanced at selected circadian times and are stimulated by melatonin
Exogenous melatonin enhances luteinizing hormone levels of women in the follicular but not in the luteal menstrual phase.
No full textTo investigate the effect of exogenous melatonin on LH pulsatility in women during the follicular and luteal menstrual phases.Randomized, double-blind placebo-controlled study.Normal cycling young women (25 to 35 years old).Each subject was admitted at the Clinical Research Center for 2 consecutive days on both the follicular and the luteal menstrual phases. On each day, at 7:00 A.M. an indwelling catether was placed in an antecubital vein for a 10 minutes blood sampling from 9:00 A.M. to 5:00 P.M. On the 2 consecutive days of both the follicular and the luteal menstrual phases, each subject randomly received either placebo or melatonin pills (1 mg at 8:00 and 0.75 mg at 10:00 and 12:00 A.M.).Luteinizing hormone pulsatility.The amplitude of LH pulses and mean LH levels were increased by melatonin in the follicular but not in the luteal menstrual phase.The stimulatory effect of exogenous melatonin on LH is modulated by the endocrine environment and selectively exerted in the follicular phase of the menstrual cycle
Acute hyperthermic effect of light on core body temperature (cBT) is mediated by melatonin suppression in women
No full textThe effect of light on core body temperature is mediated by melatonin in women.
No full textAcute exposure to bright light at night reduces the nocturnal decline of core body temperature (cBT) and inhibits melatonin secretion in men. Since inhibition of melatonin secretion by beta-adrenergic blockade reduces the nocturnal decline of cBT by 40\% in women, experiments were performed to investigate whether the thermoregulatory effect of light is mediated by modifications of melatonin secretion in cycling women. Results show that the elevation of cBT induced by nocturnal exposure to bright light (3000 lux) can be reversed completely by circumventing the decline of serum melatonin levels with concurrent oral administration of melatonin. Our finding establishes melatonin as the mediator of the effect of light on cBT in women and provides a rationale for the use of orally administered melatonin as an aid in the reentrainment of the cBT rhythm in desynchronized conditions
Melatonin enhances cortisol levels in aged women: reversible by estrogens.
No full textThe administration of melatonin increases cortisol levels in postmenopausal women. Aging and hypoestrogenism are believed to impair the regulation of the hypothalamo-pituitary-adrenal axis and may participate in the determination of this altered response. In this study the implications of hypoestrogenism were tested. Seven postmenopausal women were studied. At 08.00 hr for 2 consecutive days, each woman received randomly and in a double blind fashion a pill of placebo or melatonin (100 mg). Serum melatonin and cortisol levels were evaluated at 20 min intervals, for 48 hr. Measurements were performed in the same subjects both during no estrogen supplementation and at least two cycles of conjugated estrogens administration (0.625 mg/day). During estrogen supplementation, postmenopausal women showed slightly lower cortisol levels at lunch and early night (20.00-01.00 hr). The onset of the nocturnal melatonin rise was not modified, but that of cortisol was delayed of about 60 min (P < 0.02). The administration of melatonin elicited a marked increase in daytime cortisol levels in postmenopausal women (P < 0.02), but this stimulus completely disappeared during estrogen administration. Mean nighttime (20.00-08.00 hr) cortisol levels were not modified by daytime administration of melatonin. The present data reveal that in aged postmenopausal women, reversal of hypoestrogenism, resulting from supplemental estrogens, may improve the regulation of the hypothalamopituitary-adrenal axis
Insulin, insulin-like growth factor I (IGF-I) and IGF-II enhance basal and gonadotrophin-releasing hormone-stimulated luteinizing hormone release from rat anterior pituitary cells in vitro.
No full textThe role of insulin-like growth factor I (IGF-I) and IGF-II on luteinizing hormone (LH) release is still unclear. The present study was performed to investigate modifications of basal and gonadotrophin-releasing hormone (GnRH)-stimulated (10(-9) mol/l) LH release, induced by 4-h and a 24-h incubation with physiological doses of IGF-I (1, 5 and 10 nmol/l) and IGF-II (5, 10 and 15 nmol/l) in comparison with insulin (0.0017, 0.1722 and 1.722 nmol/l), from primary cultures of male rat anterior pituitary cells. Both during the 4-h and the 24-h incubation, basal and GnRH-stimulated LH release were increased by IGF-I, IGF-II and insulin in a dose-dependent fashion. Present data confirm insulin's capability of potentiating anterior pituitary LH release from dispersed rat anterior pituitary cells in vitro, and reveal similar effects for physiological doses of IGF-I and IGF-II
Hypothermic effect of melatonin and nocturnal core body temperature decline are reduced in aged women.
No full textIn young humans, the nocturnal rise of the hypothermic hormone melatonin generates 40-50\% of the circadian core body temperature (Tc) decline. The nocturnal Tc decline is reduced with aging in men. In this study we investigated whether a similar attenuation occurs in women and whether it is associated with a reduced serum concentration and/or action of melatonin. The circadian rhythms of melatonin and Tc (measured in the vagina) and the responses of both Tc (measured into the auricolar canal) and finger skin temperature to melatonin administration (100 mg at 0800) were investigated in two experiments involving young (22-32 yr) and aged (54-62 yr) women. In aged women, the nocturnal onset of the melatonin rise was phase advanced and Tc decline and Tc rhythm amplitude were reduced (P < 0.0005). The serum melatonin concentrations in aged women were similar to those of young women, but the melatonin capability to reduce Tc and increase skin temperature was markedly impaired. Our data show that, in women, an aging-associated reduction of temperature responses to melatonin is probably involved in inducing an attenuation of the nocturnal Tc decline and circadian Tc rhythm amplitude
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Stimulatory effect of insulin, insulin-like-growth-factor-I (IGF-I) and IGF-II on anterior pituitary LH release in vitro
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