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Biomedical subjects

A Reinberg

Publications and source records attributed to A Reinberg.

At least 109 records · Page 6Linked to original sources
PubMed1983

Differences in the seasonal rhythmicity of plasma prolactin in elderly human subjects: detection in women but not in men.

Effects of age, sex and mental condition on the circadian and circannual rhythmicity of plasma prolactin in human subjects were investigated. Circannual changes were recorded on a circadian basis in January, March, June and October in four groups of subjects: seven young men, six elderly men, six elderly women and six senile demented patients (two men and four women). Blood samples were drawn every 4 h over a 24-h period at the four sampling sessions. Circadian rhythms of the hormone were validated in all groups and at all sampling sessions except twice in elderly demented subjects. The 24-h mean levels of prolactin in plasma were approximately the same in young and elderly subjects. The circadian acrophases were most often located in the vicinity of 02.00-04.00 h. The circannual rhythmicity of the hormone showed a sex difference; the rhythm was not validated in either young or elderly men but was detected in the groups of elderly women and elderly demented patients (mainly women). The acrophases were located in May. This paper strongly suggests a sex difference in the circannual rhythmicity of plasma prolactin levels in elderly subjects.

Adult↗
PubMed1983

[Desynchronization of the circadian rhythm of oral temperature in young human subjects with poor tolerance for night work].

15 night workers (mean age, 28 years; mean seniority 1.5 years) volunteered to measure their oral temperature (clinical thermometers 0.05 degrees C precision) 5 times/24 hrs. during a 21 day span. Time series were analyzed individually according to 3 methods. 11 of the subjects with a good tolerance had (with one exception) their prominent circadian period tau equal to 24 hrs. as well as a relatively large circadian amplitude (A from 0.19 to 0.42 degrees C). By contrast, subjects with a poor tolerance (sleep disorders, persisting fatigue, psychological troubles, etc.) had a tau value ranging from 24.9 to 25.7 hrs. associated with a relatively small rhythm amplitude (A from 0.04 to 0.13 degrees C). These results support the hypothesis that a desynchronisation of circadian rhythms help to explain why certain subjects do not tolerate shiftwork.

Adult↗
PubMed1983

[Biological rhythms of thyrotropin secretion].

The rhythmic pattern of TSH secretion is now well-established and is characterized by a circadian (24 h) periodicity with a pre-sleep acrophase which is modulated by endogenous oscillators and environmental synchronisers. Among external synchronisers, the sleep-waking cycle has been extensively studied and sleep onset appears to have a negative influence on the nycthemeral TSH peak. Nutritional status may affect the TSH rhythmicity since a short term starvation induces a shift in the acrophase time. Major neurotransmitter involved in the TSH rhythms are serotonine which could be responsible for the TSH nadir. By contrast dopamine is not directly implicated in the circadian pattern of TSH secretion. TRH, the main neuropeptide controlling the thyrotrope cell, certainly has a major role in the mediation of the TSH rhythmicity. The involvement of somatostatine is less clear but as assumed for dopamine, its negative influence on TSH secretion would be stronger at the time of TSH peak than at the time of nadir. The major inhibitory effect of thyroid hormones on TSH secretion and release is evident on mean serum TSH levels but does not seem responsible for serum circadian variations. Likewise, the TSH rhythm is present in both sex and influence of estrogens and androgens would only be to modulate the mean serum TSH level. Finally the physiological influence of glucocorticoids on TSH secretion has not been clearly demonstrated.

Adult↗
PubMed1983

Alterations in circadian rhythmicity in calcium oxalate renal stone formers.

The circadian (circannual for oxalic acid) variations of 13 urinary variables (volume, creatinine, calcium, oxalic acid, glycolic acid, 17-ketosteroids, 17-hydroxycorticosteroids, phosphates, urea, uric acid, chloride, sodium, and potassium) have been documented in 7 calcium oxalate renal stone formers and 7 healthy men (control group). Urine was collected every 4 h over a period of 24 h. All subjects had the same synchronization: diurnal activity from 07(00) to 23(00) +/- 1 h and nocturnal rest; meals were given at fixed clock hours (08(00), 12(30) and 20(00) +/- 1 h). A statistically-significant rhythm (p less than 0.05) was validated for all variables except urea and calcium in healthy men. In renal stone formers, 6 variables (calcium, oxalic acid, and glycolic acid in particular) had no detectable circadian rhythm. However, a periodicity of c. 8 h (ultradian rhythm) was demonstrated for calcium and oxalic acid with peaks being located around 02(00), 10(00), and 18(00). No circannual variations in oxalic acid output could be observed. The present study shows an alteration of the periodicity of calcium and oxalic metabolisms, i.e. the loss of a circadian (24-h) rhythm and the occurrence of an ultradian rhythm of 8 h. The risk of calcium-oxalate crystallisation appears thus greater at 02(00), 10(00), and 18(00). Furthermore, any study dealing with oxalic acid excretion should state the season of urine collection when comparing renal stone formers and healthy subjects, as significant differences in oxaluria may appear during the summer months and not during the rest of the year.

Adult↗
PubMed1982

Effects of starvation on circadian variations of plasma TSH in rats.

Diurnal fluctuations of plasma TSH were investigated in ad libitum fed rats as well as after a 3 day starvation period in order to study the relationship between the circadian pattern of TSH secretion and nutritional status. Our study showed the persistence of a circadian TSH rhythm after a 3-day starvation without any change in the amplitude of plasma TSH variations. However, the 24 h average plasma TSH levels were significantly lower. A suggestive acrophase occurred at the same period of the day in starved and fed rats. Our results suggest that the control of plasma TSH concentrations and nycthemeral rhythm are not closely related and may even possibly be independent of one another.

Animals↗
PubMed1982

Adrenal circadian system in young and elderly human subjects: a comparative study.

Circadian changes in plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), total and unbound cortisol were studied in four groups: seven healthy young men, six elderly men, six elderly women and six elderly demented patients of both sexes. The daily activities of the subjects were synchronous; blood samples were taken every 4 h and 4 hourly urine samples were collected only from the young men. A circadian rhythm was defined for plasma 18-OH-DOC, total and unbound cortisol in all groups; the secretory patterns of these steroids were parallel, as were the profiles of urinary 18-OH-DOC and unconjugated cortisol. When compared with respect to sex, the 24-h mean level of total cortisol was higher in women; that of unbound cortisol was higher in the three groups of elderly patients than in the young men. No major changes in plasma steroids were observed between elderly demented patients (mainly women) and healthy elderly women. The phasing of total and unbound cortisol showed no major modifications with age, sex or senile dementia. Acrophases of 18-OH-DOC were earlier in elderly patients than in young men. Amplitudes were not modified with sex in elderly patients but were always lower in the demented patients. A circadian rhythm was defined for 18-OH-DOC, unconjugated cortisol, 17-hydroxycorticosteroids (17-OH-CS) and 17-ketosteroids in the urine of the young men. The acrophases of 18-OH-DOC and unbound cortisol were close, as were those of 17-OH-CS and 17-ketosteroids. The lag was short between the acrophases of 18-OH-DOC in plasma and urine and between those of plasma unbound cortisol and urinary unconjugated cortisol; it was much larger between the acrophases of plasma total cortisol and 17-OH-CS. Thus, the process of ageing, and the possible alterations in the central nervous system which are often seen in normal ageing, induced no major modifications in the temporal organization of adrenocortical function, even in subjects who were very advanced in age.

17-Hydroxycorticosteroids↗
PubMed1981

Circadian variations in substance P, luliberin (LH-RH) and thyroliberin (TRH) contents in hypothalamic and extrahypothalamic brain nuclei of adult male rats.

Using both the 'punch' microdissection and radioimmunological techniques, circadian variations in substance P, luliberin (LH-RH) and thyroliberin (TRH) concentrations can be statistically validated in some discrete brain regions of the (Wistar CFY) male rat investigated in May. Animals were synchronized with light from 06.00 to 18.00 h and darkness. Water and food were available ad libitum. Very well marked circadian rhythms were in evidence in brain areas where the neuronal peptides investigated are mostly present in nerve terminals in high concentrations: medial basal hypothalamus for luliberin and thyroliberin and substantia nigra for substance P. On the contrary, no significant rhythms were detected in a number of areas where luliberin (preoptic area) or substance P (preoptic area, central gray matter, amygdala, globus pallidus) synthetizing perikarya are present. This suggests that at least luliberin and substance P are not secreted according to a circadian rhythmicity. The most striking finding was that crest time locations were situated at only two different times of the day: 14.00 h for thyroliberin and 20.00 h for substance P and luliberin. This suggests that circadian variations are not solely dependent on the activity of the endocrine system.

Amygdala↗
PubMed1981

Circadian changes in the bioavailability and effects of indomethacin in healthy subjects.

Nine subjects, 19 to 29 years old (2 females) synchronized with activity from 07.00 to 00.00 received a single daily oral dose (100 mg) of indomethacin at fixed hours: 07.00, 11.00, 15.00, 19.00 and 23.00, in random order and at weekly intervals. 1) Chronopharmacokinetics: Venous blood (sampled at: 0, 0.33, 0.67, 1.0, 1.5, 2.0, 4.0, 6.0, 8.0 and 10.0 h post ingestion) was used for plasma drug determination. Circadian changes in peak height, time to peak, area under the concentration-time curve and the disappearance rate were used to characterize indomethacin chronopharmacokinetics. A circadian rhythm of both peak height and time to peak was validated. An evening ingestion led to smallest peak height and longest time to peak. 2) Circadian changes in a set of effects: Eleven physiologic variables were investigated (post absorption) at delta t = 2 h. Circadian rhythms were detected: i) on control day and ii) with evening ingestion for ten of the eleven variables indicating that the subjects' temporal structure did not become altered by an evening ingestion, whereas it did become so by morning ones. Transient changes (n minutes post absorption) measured as T240 min post absorption/Tcontrol day, same clock hour ratio were also circadian rhythmic for most variables. Again, evening ingestion appeared least disturbing.

Adult↗
PubMed1981

Age- and mental health-related circadian rhythms of plasma levels of melatonin, prolactin, luteinizing hormone and follicle-stimulating hormone in man.

Circadian changes in plasma levels of melatonin, prolactin, LH and FSH were studied in four groups: seven healthy young men, six elderly men, six elderly women and six elderly demented patients (two men and four women). The daily activities of the subjects were synchronous and blood samples were taken every 4 h. The 24-h mean concentrations of prolactin in plasma were the same in all groups, whereas those of LH and FSh were twice as high in the elderly as in the young men and eight and 23 times higher respectively in the elderly women. The 24-h mean plasma levels of melatonin in the elderly were half those in the young, but were not influenced by the sex or mental condition of the subjects. A statistically significant circadian rhythm for melatonin was defined in the four groups, for prolactin in all groups except the elderly men and for LH only in the demented patients and in the young men. No circadian rhythm could be detected for FSH in any of the four groups. The acrophases of melatonin and prolactin ranged between 02.30 and 04.00 h, those of LH (when a rhythm was validated) clustered around 01.00 h. The circadian rhythms of plasma levels of melatonin, prolactin and LH are not modified in old age nor in dementia. A positive correlation has been demonstrated in young men between melatonin and LH and between melatonin and prolactin, but no such correlation could be found in the elderly.

Adult↗
PubMed1981

Clinical chronopharmacology.

Circadian (approximately or equal to 24 h), circannual (approximately or equal to 1 year) and other biological rhythms of endogenous origin, detectable at all levels of organization, constitute a temporal structure in all animal species, including man. Circadian, circannual and other rhythmic changes in biological susceptibility and response of organisms to a large variety of physical as well as chemical agents including medications and foods are rather common phenomena. Modern chronopharmacology investigates drug effects: a) as a function of biological timing and b) upon parameters characterising the endogenous bioperiodicities. A better understanding of periodic and thus predictable changes in drug effects can be attained through consideration of three complementary concepts: the chronokinetics of a drug (rhythmic changes in its pharmacokinetics): the chronesthesy (rhythmic changes in susceptibility of target biosystem to this drug), and the chronergy (the drug-integrated overall effects). One of the aims of chronopharmacology is solving problems of drug optimization. Knowledge of those administration times coinciding with best effectiveness or tolerance is required to optimize both timing(s) and dosage(s) of a medication. Illustrative examples of both experimental and clinical investigative chronopharmacology are corticosteroids and anticancerous agents.

Adult↗
PubMed1980

Circadian variation of adrenocortical cyclic nucleotides (cyclic AMP and cyclic GMP) in hypophysectomized rats.

The existence of a circadian variation in the adrenocortical concentrations of cyclic AMP and cyclic GMP in male adult Wistar rats examined 10 days after hypophysectomy is demonstrated. The results suggest that the circadian variations of adrenocortical cyclic nucleotides observed previously in intact rats might not entirely depend upon pituitary corticotrophin.

Adrenal Cortex↗
PubMed1979

Circannual and circadian rhythms in the concentration of corticosterone in the plasma of the edible frog (Rana esculenta L.).

For a period of 21 months between May 1974 and September 1976, circadian variations in the plasma concentration of corticosterone were studied by competitive protein-binding techniques in mature male and female edible frogs living in their natural environment. Blood samples were taken from 8 to 12 frogs six times daily and conventional and cosinor methods were used for statistical analysis. Circadian rhythms were not detected during February and March (time of hibernation). Circannual rhythms were detected in three parameters of the circadian rhythm. The mean concentration of corticosterone over a 24 h period (24 h mean) reached a peak on 1 May (between 15 April and 15 May; 95% limits of confidence); the annual mean value of the 24 h means was 1.97 +/- 0.25 (S.E.M.) microgram/100 ml, with an amplitude of 0.66 microgram/100 ml (0.53--0.79 microgram/100 ml; 95% limits of confidence). Circadian variations in the concentration of corticosterone were largest in May (peak of reproductive activity). The times at which the peak concentration of corticosterone occurred showed circannual variations: peak values were detected around 24.00 h in May, 19.00 h in July and 08.00 h in November. Both circadian and circannual variations have therefore been demonstrated in an endocrine function of an amphibian in its natural habitat.

Animals↗