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Possible influence of melatonin on the human prolactin circadian secretory pattern
No full textIn humans, prolactin (PRL) shows a circadian secretory
pattern characterized by a sleep-dependent rising plasma
level. In particular, PRL rises are related to non-rapid eye
movement sleep (NREMS), even though there is a
progressive rise during the night with the highest plasma
levels in the second half of nocturnal sleep just when
NREMS is less prevalent. In previous work we found that PRL rises were linked to slow wave sleep (SWS). Furthermore, we observed a statistically significant PRL circadian secretory pattern (i.e., the presence of a circadian rhythm) only in "good sleepers" (i.e., subjects having an "effìcient" sleep). In such subjects, the most commonly used "sleep efficiency index" (i.e., the ratio: (SWS + REMS)/(total sleep time); normal range, 0.35-0.60) showed values greater than 0.35. On the contrary, "poor sleepers", with an efficiency index inferior to 0.35, did not demonstrate the presence of a PRL rhythm. A circadian secretory pattern has also been found for
melatonin (MT) , to date, the most investigated substance
produced by the pineal gland. Even though there are
some discordant data, in the case of a normal recurrence of
light-dark and wake-sleep cycles, a MT plasma level
increase would usually be detectable in the first half of
nocturnal sleep and therefore would occur before the PRL
rise. The aim of this study was to evaluate whether MT is
involved in the regulation of the PRL circadian secretory
rhythm. Subjects and methods: Eight healthy volunteers,
considered as controls (five males and three females; mean
age, 34 years; range 20-41 years), and eight patients with
neuroradiological evidence of pineal tumour (six males and
two females; mean age, 33 years; range, 18- 38 years) were
examined. The latter were collected in a time interval of 5
years. In such patients, the histological diagnosis was one of a well-differentiated, low-grade fibrillary astrocytoma, noninvasive and, in five cases, sharply circumscribed (benign
astrocytomas). All the patients presented no neurological or
psychopathological symptoms during the testing period.
After two adaptation nights, each subject underwent an
all-night polysomnogram (EEG, EOG, EMG) from 22:00 to
07:00 with the lights off. Sleep was scored according to
standard criteria. Blood samples were drawn every 15
min. In all subjects PRL and MT plasma levels were
measured by a homologous double antibody radioimmunoassay (RIA). A week before and during the 3 days spent in the sleep laboratory, the duration of light-dark and wake-sleep cycles, physical activity, and diet were
standardized by a pre-established schedule. All the subjects underwent testing either in spring or autumn and the women
during the follicular phase of their menstrual cycle.
PRL and MT chronobiological characteristics were
determined by the single and population mean-cosinor
methods: i.e., the 24 h cosine function of a continuous curve
best fitted by least-squares analysis in the case of an
individual or group, respectively. Such methods provide
the possible statistical significance of a circadian secretory
curve: i.e., the presence of a rhythm according to the Fvalue
for zero amplitude test. Both the individual and group
circadian curves are characterized by the following
parameters: (a) mesor - 24 h average obtained by the best
fitting cosine function used to approximate the circadian
curve; (b) amplitude - difference between the maximum
value measured at acrophase and the mesor in the cosine
curve; (c) acrophase - crest timing of the best fitted curve.
Results: All healthy volunteers showed PRL and MT
circadian secretory rhythms. The presence of a PRL
circadian rhythm is likely due to the presence of efficient
sleep. On the contrary, in all the patients with a pineal
tumour MT circadian plasma levels were inferior to the RIA
normal minimum value and therefore the cosinor methods
failed to show significant MT curves. In addition, such
patients did not exhibit a PRL circadian rhythm even though
their sleep efficiency index was within the normal range.
Furthermore, they allow the detection ofa possible PRL circadian rhythm. Our data demonstrate the need for a polygraphic study of sleep to show the presence of a PRL circadian rhythm that in fact is detectable only in subjects having efficient sleep (sleep efficiency index greater than 0.35). Furthermore, the results concerning patients with pineal tumours permit one to nypothesize that, among possible circadian systems (regulating PRL rhythm, an important role is probably played by the pineal gland through MT. Since the PRL rhythm is sleep-dependent, it seems reasonable to infer that the nocturnal entrainment process is mediated by the pineal gland. Of course, an action by other substances (together with or independent from MT) produced by the pineal gland cannot be excIuded. Such a hypothesis awaits further examination by future research. In order to explain the possible influence of MT on PRL circadian rhythm we could suggest that in humans the PRL acrophase while it has been pointed out that in some animals pinealectomy abolishes the PRL circadian rhythm and MT enhances the PRL nocturnal secretion. On the other hand, in addition to normal PRL plasma levels, the group of patients with pineal tumors presented a normal behavioral pattern as far as the recurrence of the wake-sleep cycle and the organization of sleep cycles were concerned. Such results suggest that MT does not influence the hypothalamic- pituitary mechanisms involved in overall PRL circadian secretion and, according to others, either the wake - sleep cycle or the systems controlling the quantity and quality of sleep
Importance of sleep and melatonin for the human prolactin circadian secretory pattern in normal and pathological conditions
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Age-related modifications of the human growth hormone circadian secretory pattern studied with a new statistical method in healthy adults
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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