Melatonin phase-shifts human circadian rhythms with no evidence of changes in the duration of endogenous melatonin secretion or the 24-hour production of reproductive hormones

The pineal hormone melatonin is a popular treatment for sleep and circadian rhythm disruption. Melatonin administered at optimal times of the day for treatment often results in a prolonged melatonin profile. In photoperiodic (day length-dependent) species, changes in melatonin profile duration influence the timing of seasonal rhythms. We investigated the effects of an artificially prolonged melatonin profile on endogenous melatonin and cortisol rhythms, wrist actigraphy, and reproductive hormones in humans. Eight healthy men took part in this double-blind, crossover study. Surge/sustained release melatonin (1.5 mg) or placebo was administered for 8 d at the beginning of a 16-h sleep opportunity (1600 h to 0800 h) in dim light. Compared with placebo, melatonin administration advanced the timing of endogenous melatonin and cortisol rhythms. Activity was reduced in the first half and increased in the second half of the sleep opportunity with melatonin; however, total activity during the sleep opportunities and wake episodes was not affected. Melatonin treatment did not affect the endogenous melatonin profile duration, pituitary/gonadal hormone levels (24-h), or sleepiness and mood levels on the subsequent day. In the short term, suitably timed sustained-release melatonin phase-shifts circadian rhythms and redistributes activity during a 16-h sleep opportunity, with no evidence of changes in the duration of endogenous melatonin secretion or pituitary/gonadal hormones.     

Circadian variations in plasma levels of hypophyseal, adrenocortical and testicular hormones in men infected with human immunodeficiency virus

Alterations in the circadian time structure of the secretion of several hormones were investigated in 13 male patients infected with human immunodeficiency virus (HIV). Seven were asymptomatic (classified CDC II, according to the criteria of the Atlanta Centers for Disease Control), and 6 had acquired immunodeficiency syndrome (CDC IV). Ten healthy males volunteered as controls. Plasma levels of dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S), cortisol, testosterone, ACTH, and beta-endorphin were determined by RIA in blood samples obtained every 4 h from 0830-0830 h the next morning. Data were analyzed both by two-way analysis of variance and the cosinor method. Circadian rhythms were statistically validated for each of the six hormones in each of the three groups of subjects. Compared with the control subjects, mesors (24-h adjusted means) were significantly higher for cortisol and lower for DHEA, DHEA-S, and ACTH (P less than 0.001 for all four hormones) in all HIV-infected patients. Plasma testosterone mesors were similar in controls and CDC II patients, but decreased significantly in the CDC IV patient group (P less than 0.05). Analysis of the circadian rhythms of plasma hormone levels clearly indicated an altered adrenal hormonal state in HIV-infected male patients, even during the asymptomatic period of the infection. For instance, plasma cortisol at 0430 h was more than twice as high in HIV-infected patients as it was in time-qualified controls. Although patients already had elevated plasma cortisol and lowered adrenal androgen levels at this stage, hypogonadism was not observed, as gauged by plasma testosterone concentrations. We speculate that the primary hormonal defect in HIV-infected patients is increased cortisol secretion resulting from circadian-varying stimulation of the adrenal cortex by a factor other than pituitary ACTH. This factor might be a stimulating substance secreted primarily by infected immune cells. Excess cortisol would lower adrenal androgen secretion by shifting adrenal steroid biosynthesis toward glucocorticoids and decreasing pituitary ACTH secretion via a negative feedback mechanism.     

Circadian rhythms of atrial natriuretic peptide, renin, aldosterone, cortisol, blood pressure and heart rate in normal and hypertensive subjects

The occurrence and extent of a circadian rhythm in the circulating concentrations of atrial natriuretic peptide (ANP) are still matters of controversy. Only a few data are available in humans relating the time structure of plasma ANP levels with the circadian patterns of other hormones and cardiovascular variables. In a group of hospitalized normal volunteers (six men and four women, 16-76 years old), and in a group of hospitalized hypertensives (seven men and three women, 18-76 years old), we investigated the circadian variability of ANP and its temporal relationship with the circadian rhythms of blood pressure (BP) and heart rate (HR), and plasma renin activity (PRA), plasma aldosterone (PA) and plasma cortisol (PC) levels, by using a chronobiological inferential statistic method. At the end of a synchronizing period of 1 week (the diet and daily schedule were standardized), the subjects underwent automatic BP and HR monitoring, and blood sampling for 24 h. A statistically significant mean circadian rhythm was demonstrated for ANP, BP, HR, PRA, PA and PC in both normal and hypertensive subjects. The mean circadian acrophase of ANP (calculated to occur at around 04.00 h) anticipated the corresponding acrophases of the other hormones; BP and HR rhythms appeared to be in antiphase with ANP rhythm, i.e. the peak of BP and HR rhythms more or less coincided with the trough in ANP rhythm. A significant increase in the daily levels (assessed by the circadian mesor) of ANP was present in hypertensive subjects when compared with normal controls. In essential hypertension the circadian rhythm of ANP was set at higher circulating levels, but otherwise it was similar to the circadian rhythm found in normals. ANP mesors correlated significantly with renin and aldosterone mesors in normal subjects but not in hypertensive patients. ANP appears to anticipate awakening in its circadian periodic rise. On the basis of the considerable acrophase asynchronism, it seems possible to exclude any causal relations between the periodic changes of ANP and the rhythmic fluctuations of the other hormones that we studied. In contrast, important relations may be hypothesized between ANP levels and BP and HR values, on the basis of their antiphase rhythms.     

Twenty-four hour rhythm of melatonin in patients with a history of pineal and/or hypothalamo-neurohypophyseal germinoma

Abstract: Melatonin deficiency after a pinealectomy has been investigated in animals; however, in humans, this status can be assessed solely by investigating patients with a tumor originating in the pineal gland. This study analyzes secretion of melatonin and pituitary hormones in 14 patients with germinoma originating in the pineal or the hypothalamic-neurohypophyseal region. Thirteen patients had been successfully treated prior to this study. One patient was included in this study before the initiation of treatments. Plasma sampling was performed every 2 hr for 24 hr and melatonin concentrations were measured by radioimmunoassay. Melatonin secretion was nearly absent in the patients with pineal germinoma regardless of treatment option, even in the patient who had been untreated. In contrast, melatonin secretion and its circadian rhythms were not affected in patients with a hypothalamo-neurohypophyseal germinoma. The circadian rhythms of growth hormone and adrenocorticotropic hormone were not dysregulated in patients with the melatonin deficiency. We conclude that germinoma cells originating the pineal gland impair the production of melatonin by pineocytes and consequently induce a permanent melatonin deficiency in those patients. Since melatonin exerts multiple physiological functions, once a clinical concept of "melatonin deficiency syndrome" is established, melatonin replacement therapy could be investigated in patients who have a pineal germinoma or who have undergone a neurosurgical pinealectomy.     

Age-related alterations in the circadian rhythms of pulsatile luteinizing hormone and testosterone secretion in healthy men

The effect of advancing age on the chronobiology of testosterone (T) and luteinizing hormone (LH) secretion in healthy men was investigated. Twenty young (average age 30.4 yrs) and 14 elderly (average age 70.4 yrs) men underwent 10 min blood sampling for 25 hrs to evaluate the circadian periodicity of LH, LH pulse frequency, and T. Using cosinor regression analysis, young men were found to have a significant (p less than .05) circadian variation in LH pulse frequency, with slowing of LH pulses during the night (maximum slowing at 2230 hr). There was also a tendency for LH pulse amplitude to increase at night (p = .06) in young men. However, no significant circadian pattern in LH pulse frequency or amplitude was detected in the elderly men. Mean LH by radioimmunoassay (RIA) and bioassay did not vary over the 24-hr period in either age group. Both young and elderly men had significant circadian rhythms in serum T, although the rhythm in elderly men was considerably blunted and was shifted in time compared to the young. These data provide evidence for age-related changes in the circadian rhythms of LH pulse frequency and T secretion and suggest that the LHRH pulse generator loses its circadian rhythmicity with normal aging in men.     

Seasonal rhythms of plasma gonadotrophins: their persistence in elderly men and women

Circannual changes of immunoreactive LH and FSH were documented 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 men and women suffering from senile dementia. The sampling was serially dependent only for the young men and the core subgroups of elderly men and elderly women. A circadian rhythm for FSH was not detected in any group of subjects during any of the sampling sessions, whereas a circadian rhythm for LH was detected twice (June and October) in young men, once (October) in elderly demented patients, and not at all in the groups of elderly men and women. Both 24-h and yearly mean levels of gonadotrophins were higher in elderly subjects (two-to 25-fold according to the hormone, sex and season) than in young men. Circannual rhythms of plasma LH with large amplitudes were validated by the cosinor method, with an acrophase located in April or May. A circannual rhythm of plasma FSH was validated only in young men, with an acrophase in October. The persistence of a circannual rhythm of plasma LH with large amplitude in elderly subjects, associated with high mean levels of the hormone, especially in elderly women, suggests that this bioperiodicity of the pituitary gland is independent of gonadal function.     

Light exposure induces equivalent phase shifts of the endogenous circadian rhythms of circulating plasma melatonin and core body temperature in men.

Release of melatonin into the circulation by the pineal occurs almost exclusively during the nighttime hours. It has been proposed that this daily rhythm, like that of body temperature, reflects the output of a central circadian pacemaker in humans. In order to investigate the relationship of the circadian rhythms of body temperature and melatonin in humans and compare their resetting responses to light, we characterized the endogenous 24-h profiles of these rhythms in eight young male adults during constant routines before and after exposure to a stimulus consisting of bright light, room light, and darkness/sleep. We found that the time of the fitted maximum of the endogenous melatonin rhythm consistently preceded the fitted temperature minimum by a mean +/- SE of 1.8 +/- 0.2 h. Bright-light exposure induced substantial and equivalent phase shifts of the melatonin and temperature rhythms (mean +/- SE difference in the phase-shifting response, 0.03 +/- 0.32 h), and the body temperature and melatonin rhythms thus maintained their usual phase relationship even after light-induced circadian phase inversion. These results are consistent with the hypothesis that the endogenous circadian components of both the plasma melatonin and body temperature rhythms are generated by a single central circadian pacemaker in humans. Furthermore, using the time of the fitted temperature minimum as a reference standard, we found that the fitted maximum of the endogenous 24-h melatonin profile was a more reliable phase marker than the onset of the nocturnal rise of melatonin (F = 4.48; P less than 0.01).     

Circadian rhythm abnormalities in totally blind people: incidence and clinical significance.

When people are completely isolated from environmental time cues, their circadian rhythms free run with a nearly 24-h cycle, generated by an internal body clock. Free-running temperature, cortisol, and melatonin rhythms have also been described in totally blind people, even though they were living in normal society and had access to abundant time cues; thus an intact visual system may be essential for synchronization of the circadian system. However, because of the small numbers of subjects studied, the incidence and clinical significance of circadian rhythm abnormalities among the blind has remained uncertain. In this study, plasma melatonin (n = 20), cortisol (n = 4), and sleep propensity (n = 1) were measured in serial samples taken from totally blind subjects for 24 h. Most totally blind subjects had circadian rhythm abnormalities. In about half of the subjects, the rhythms were free-running. Some blind subjects suffered recurrent insomnia and daytime sleepiness that were maximal when the internal rhythms were out of phase with the preferred sleep times. The high incidence of abnormal circadian rhythms in blind people underscores the importance of the light-dark cycle as an important environmental synchronizer for the human circadian system.     

The role of granulocyte-macrophage-colony stimulating factor, cortisol, and melatonin in the regulation of the circadian rhythms of peripheral blood cells in healthy volunteers and patients with breast cancer

The circulating blood cells show highly reproducible circadian rhythms. However, the factors that regulate these rhythms are not well understood. In the current study, we examined the diurnal variations of peripheral blood cells (white blood cells, neutrophils, lymphocytes), granulocyte-macrophage-colony stimulating factor (GM-CSF), and melatonin levels, and considered the role of melatonin on these rhythms in healthy volunteers and in patients with early breast cancer. Fourteen premenopausal patients with early stage breast cancer (T2, N1 tumors) and 10 premenopausal healthy volunteers were included in the study. Blood samples were taken every 4 hr for a period of 24 hr. Peripheral blood cells were counted by automated analyser and also from peripheral blood films. GM-CSF levels were measured by ELISA and melatonin levels by radioimmunoassay (RIA). Serum melatonin, cortisol, and GM-CSF levels, and peripheral blood cell counts showed significant circadian rhythms in healthy volunteers. Except for GM-CSF, these circadian rhythms were found not to be suppressed in early breast cancer patients. While there were significant correlations of serum GM-CSF and cortisol levels with peripheral blood cell counts in healthy volunteers, only lymphocyte counts were found to be significantly correlated with serum GM-CSF and cortisol levels in patients with breast cancer. Serum melatonin levels were found to be significantly correlated with lymphocyte counts in both groups. Our results suggest that peripheral blood cells show significant circadian rhythms in both healthy volunteers and in patients with stage II (T2, N1) breast cancer, and GM-CSF, cortisol, and melatonin may have a role in the regulation of peripheral blood cell counts.     

Pituitary hormone circadian rhythm alterations in cirrhosis patients with subclinical hepatic encephalopathy

AIM： To analyze pituitary hormone and melatonin circadian rhythms, and to correlate hormonal alterations with clinical performance, hepatic disease severity and diagnostic tests used for the detection of hepatic encephalopathy in cirrhosis. METHODS： Twenty-six patients with cirrhosis were enrolled in the study. Thirteen patients hospitalized for systemic diseases not affecting the liver were included as controls. Liver disease severity was assessed by the Child-Pugh score. All patients underwent detailed neurological assessment, electroencephalogram （EEG）, brain magnetic resonance imaging （MRI）, assays of pi- tuitary hormone, cortisol and melatonin, and complete blood chemistry evaluation. RESULTS： Pituitary hormone and melatonin circadian patterns were altered in cirrhosis patients without clinical encephalopathy. Circadian hormone alterations were different in cirrhosis patients compared with controls. Although cortisol secretion was not altered in any patient with cirrhosis, the basal cortisol levels were low and correlated with EEG and brain MRI abnormalities. Melatonin was the only hormone associated with the severity of liver insufficiency. CONCLUSION： Abnormal pituitary hormone and melatonin circadian patterns are present in cirrhosis before the development of hepatic encephalopathy. These abnormalities may be early indicators of impending hepatic encephalopathy. Factors affecting the human biologic clock at the early stages of liver insufficiency require further study.     

Circadian timekeeping during pregnancy: endogenous phase relationships between maternal plasma hormones and the maternal body temperature rhythm in pregnant rhesus monkeys.

Nine pregnant rhesus monkeys maintained in constant low level lighting (5 Lux) from 56-80 days gestation (dGA) onward were studied to assess the presence or absence of circadian maternal body temperature and maternal plasma hormone variations. Maternal arterial blood samples were taken every 4 h in six monkeys (105-120 dGA) for 48-56 h and every 2 h in three monkeys (108-115 dGA) for 60 h. Maternal intraabdominal temperature was recorded continuously. Cosinor analysis was used to determine circadian rhythmicity. Individual endogenous timekeeping was demonstrated by 1) free-running circadian variations in maternal body temperature in all nine animals, 2) consistent internal acrophase relationships between the maternal body temperature and maternal plasma cortisol rhythm, and 3) idiosyncrasy of the temporal relationship of detectable rhythms to the external environment in individual animals. Only one animal had a significant maternal plasma ACTH rhythm, whereas the presence of 24-h variations in the other hormones varied in individual animals. The mean +/- SD acrophase profiles in hours from the temperature acrophase in those animals who showed significant rhythms were 19.7 +/- 0.6 (n = 8) for cortisol, 19.4 +/- 2.4 (n = 6) for dehydroepiandrosterone sulfate, 8.3 +/- 1.1 (n = 6) for progesterone, and 18.9 +/- 1.6 (n = 3) for estradiol. We conclude that 24-h variations in maternal plasma hormones are truly endogenously generated and not passively dependent on the light-dark cycle. The maternal circadian system regulates the 24 h temporal organization of endogenous plasma hormone variations. We hypothesize that rhythms in cortisol, dehydroepiandrosterone sulfate, progesterone, and estradiol during pregnancy are directly or indirectly governed by the maternal hypothalamus via the circadian oscillatory output of the maternal adrenal.     

Melatonin administration can entrain the free-running circadian system of blind subjects

Although melatonin treatment has been shown to phase shift human circadian rhythms, it still remains ambiguous as to whether exogenous melatonin can entrain a free-running circadian system. We have studied seven blind male subjects with no light perception who exhibited free-running urinary 6-sulphatoxymelatonin (aMT6s) and cortisol rhythms. In a single-blind design, five subjects received placebo or 5 mg melatonin p.o. daily at 2100 h for a full circadian cycle (35-71 days). The remaining two subjects also received melatonin (35-62 days) but not placebo. Urinary aMT6s and cortisol (n=7) and core body temperature (n=1) were used as phase markers to assess the effects of melatonin on the During melatonin treatment, four of the seven free-running subjects exhibited a shortening of their cortisol circadian period (tau). Three of these had taus which were statistically indistinguishable from entrainment. In contrast, the remaining three subjects continued to free-run during the melatonin treatment at a similar tau as prior to and following treatment. The efficacy of melatonin to entrain the free-running cortisol rhythms appeared to be dependent on the circadian phase at which the melatonin treatment commenced. These results show for the first time that daily melatonin administration can entrain free-running circadian rhythms in some blind subjects assessed using reliable physiological markers of the circadian system.     

Effect of MT1 melatonin receptor deletion on melatonin-mediated phase shift of circadian rhythms in the C57BL/6 mouse

In the mouse suprachiasmatic nucleus (SCN), melatonin activates MT1 and MT2 G-protein coupled receptors, which are involved primarily in inhibition of neuronal firing and phase shift of circadian rhythms. This study investigated the ability of melatonin to phase shift circadian rhythms in wild type (WT) and MT1 melatonin receptor knockout (KO) C57BL/6 mice. In WT mice, melatonin (90 microg/mouse, s.c.) administered at circadian time 10 (CT10; CT12 onset of activity) significantly phase advanced the onset of the circadian activity rhythm (0.60 +/- 0.09 hr, n = 41) when compared with vehicle treated controls (-0.02 +/- 0.07 hr, n = 28) (P < 0.001). In contrast, C57 MT1KO mice treated with melatonin did not phase shift circadian activity rhythms (-0.10 +/- 0.12 hr, n = 42) when compared with vehicle treated mice (-0.12 +/- 0.07 hr, n = 43). Similarly, in the C57 MT1KO mouse melatonin did not accelerate re-entrainment to a new dark onset after an abrupt advance of the dark cycle. In contrast, melatonin (3 and 10 pm) significantly phase advanced circadian rhythm of neuronal firing in SCN brain slices independent of genotype with an identical maximal shift at 10 pm (C57 WT: 3.61 +/- 0.38 hr, n = 3; C57 MT(1)KO: 3.45 +/- 0.11 hr, n = 4). Taken together, these results suggest that melatonin-mediated phase advances of circadian rhythms of neuronal firing in the SCN in vitro may involve activation of the MT2 receptor while in vivo activation of the MT1 and possibly the MT2 receptor may be necessary for the expression of melatonin-mediated phase shifts of overt circadian activity rhythms.     

Circadian rhythms of ocular melatonin in the wrasse Halichoeres tenuispinnis, a labrid teleost

Using in vivo and in vitro methods we studied the regulation of ocular melatonin rhythms in the wrasse Halichoeres tenuispinnis, by either light or the circadian clock. Rhythmic changes in ocular melatonin levels under light-dark (LD) cycles were persistent under constant darkness (DD), and had a circadian periodicity of approximately 24h. However, ocular melatonin levels remained low under constant light conditions. When wrasse were exposed to a single 6-h light pulse at three different circadian phases under DD, phase-dependent phase shifts in the circadian rhythms of ocular melatonin were observed. When eyecups were prepared during mid-light periods or at the onset of darkness, and incubated in vitro in either light or dark periods, both time and light conditions affected melatonin release. These results indicate that the melatonin rhythms in the wrasse eye are driven by an ocular circadian clock that is entrained to LD cycles via local photoreceptors.     

Patterns of plasma melatonin with ageing and mental condition: stability of nyctohemeral rhythms and differences in seasonal variations

Effects of ageing and mental condition on the nyctohemeral and seasonal rhythms of plasma melatonin in human subjects were investigated. Four groups of subjects were formed for a transverse study: 7 healthy young men (24 years), 6 elderly women, 6 elderly men and 6 elderly patients (2 men and 4 women) suffering from senile dementia (70-80 years). The subjects were synchronized. Blood samples were taken every 4 h during 24 h in January, March, June and October. In comparison to young men, the plasma levels of melatonin were markedly decreased (by about one half) in elderly subjects without any difference according to sex or mental condition. Nyctohemeral rhythms of the hormone were validated in all groups and at all sampling sessions. The nyctohemeral acrophases were remarkably stable (around 03.00 h) whatever the season, age or sex. A seasonal variation was found in all groups (except elderly women) with differences between young and elderly subjects: plasma melatonin levels were significantly lower in January than in June in young men, whereas in elderly subjects they were significantly lower in October than in January/March. No significant difference was observed in mesor, amplitude or acrophase of nyctohemeral and seasonal rhythms of plasma melatonin in patients with senile dementia when compared with healthy elderly subjects. The stability of the nyctohemeral peak time whatever the age group or season as opposed to the differences in the seasonal pattern of plasma melatonin according to the age groups raises the problems of both outdoor photoperiod and ageing in ruling the secretion of melatonin in man.     

Do plasma melatonin concentrations decline with age?

PURPOSE: Numerous reports that secretion of the putative sleep-promoting hormone melatonin declines with age have led to suggestions that melatonin replacement therapy be used to treat sleep problems in older patients. We sought to reassess whether the endogenous circadian rhythm of plasma melatonin concentration changes with age in healthy drug-free adults. METHODS: We analyzed the amplitude of plasma melatonin profiles during a constant routine in 34 healthy drug-free older subjects (20 women and 14 men, aged 65 to 81 years) and compared them with 98 healthy drug-free young men (aged 18 to 30 years). RESULTS: We could detect no significant difference between a healthy and drug-free group of older men and women as compared to one of young men in the endogenous circadian amplitude of the plasma melatonin rhythm, as described by mean 24-hour average melatonin concentration (70 pmol/liter vs 73 pmol/liter, P = 0.97), or the duration (9.3 hours vs 9.1 hours, P = 0.43), mean (162 pmol/liter vs 161 pmol/liter, P = 0.63), or integrated area (85,800 pmol x min/liter vs 86,700 pmol x min/liter, P = 0.66) of the nocturnal peak of plasma melatonin. CONCLUSION: These results do not support the hypothesis that reduction of plasma melatonin concentration is a general characteristic of healthy aging. Should melatonin replacement therapy or melatonin supplementation prove to be clinically useful, we recommend that an assessment of endogenous melatonin be carried out before such treatment is used in older patients.     

Circadian pattern of circulating plasma ACTH, cortisol, and aldosterone in patients with beta-thalassemia

Plasma levels of ACTH, cortisol, and aldosterone were measured for an entire day every 2 h, starting from midnight, in 4 healthy subjects, and in 4 patients with beta-thalassemia, without evidence for any endocrine disease. The subjects, after synchronized standard life conditions for 10 days, were held in constant supine position during the study. The data were analysed by the "cosinor" method. The results show significant circadian rhythms for the three biological variables in healthy subjects. In the thalassemic patients a significant circadian rhythm was detected only for cortisol and aldosterone. No rhythm was demonstrated for ACTH in the patient group. While no differences were found in mesors and acrophases for the three hormones between the two groups, a significant difference was observed regarding amplitudes. These data suggest that in beta-thalassemia, the secretion rhythmicity of ACTH is modified, whereas the adrenal cortex maintains its own physiologic rhythmicity in hormone secretion.     

Correlation between urinary cortisol and 6-sulphatoxymelatonin rhythms in field studies of blind subjects

OBJECTIVE: Blind individuals have different types of circadian rhythm disorders. In order to study these in the field reliable markers of circadian phase are required. The aim of the present study was to determine the usefulness of urinary cortisol as a marker rhythm in field studies. This was assessed by investigating the relationship between the cortisol rhythms and the previously determined melatonin rhythms from a large sample of blind people with different types of circadian rhythm disorders. DESIGN: Field study SUBJECT: Registered blind subjects (n = 49) classified as having light perception or better (n = 19, 12 men, 7 women, aged 23-61 years) or having no conscious perception of light (n = 30, 24 men, 6 women, aged 19-72 years) were studied in their normal environment. MEASUREMENT: Sequential 4-hourly urine samples (plus an overnight sample) were collected for 48 h each week for 3-5 weeks. Urinary cortisol and 6-sulphatoxymelatonin were measured by radioimmunoassay. RESULT: Irrespective of the type of circadian rhythm (entrained or free-running), there was a significant correlation between the characteristics of the 6-sulphatoxymelatonin and cortisol rhythms in the blind subjects. CONCLUSION: Urinary cortisol is recommended as a useful marker of circadian phase in field studies in addition to urinary 6-sulphatoxymelatonin measurements.     

Effects of GH replacement on 24-h ambulatory blood pressure and its circadian rhythm in adult GH deficiency

OBJECTIVE: Increased prevalence of hypertension and cardiovascular mortality have been reported in hypopituitary patients who had been appropriately replaced with conventional pituitary hormones except GH. Growth hormone replacement (GHR) results in improvement of surrogate markers of cardiovascular function. Data on effects of GHR on blood pressure (BP) in adult growth hormone deficiency (AGHD), however, remain contradictory. There are as yet no reports on BP circadian rhythms in untreated or treated AGHD. Therefore, in a 12-month follow-up study, we evaluated the effects of GHR on ambulatory blood pressure (ABP) in AGHD patients. STUDY DESIGN: A prospective, open treatment design study to determine the effects of GHR on ABP and heart rate in AGHD patients. GH was commenced at a daily dose of 0.5 IU, and titrated up by increments of 0.25 IU at 4-weekly intervals to achieve and maintain IGF-I standard deviation score (IGF-I SD) between the median and upper end of the age-related reference range. PATIENTS: Twenty-two, post-pituitary surgery, severe AGHD patients (11 men), defined as peak GH response < 9 mU/l to provocative testing were recruited. The mean age +/- SEM was 48.8 +/- 2.5 years. Twenty-one patients required additional pituitary replacement hormones following pituitary surgery and were on optimal doses at recruitment. MEASUREMENTS: Twenty-four-hour ABP and heart rate (HR), body mass index (BMI), waist hip ratio (WHR) and total body water (TBW) were measured before and after 12 months on GHR. Cosinor analysis was used to analyse BP and HR circadian rhythm parameter estimates. RESULTS: Target IGF-I SD was achieved within 3 months of commencement of GHR in all patients (-3.5 +/- 0.4 at baseline vs. 0.8 +/- 0.2 at 3 months, P < 0.001) and remained within range at 12 months (1.1 +/- 0.2, P < 0.001 compared to baseline). A significant increase in TBW (45.8 +/- 1.2 vs. 47.8 +/- 1.5 kg, P < 0.05) but no significant change in BMI (30.7 +/- 2.2 vs. 31.8 +/- 2.7, P = NS) or WHR (0.95 +/- 0.02 vs. 0.93 +/- 0.02, P = NS) was observed after 12 months on GHR. The 24-h mean systolic ABP (SBP; 126.2 +/- 2.8 vs. 120.1 +/- 2.7 mmHg, P < 0.001) and diastolic ABP (DBP; 78.2 +/- 1.6 vs. 71.4 +/- 1.8 mmHg, P < 0.001) significantly decreased following GHR with a parallel increase in 24-h mean HR (69.6 +/- 2.5 vs. 73.8 +/- 2.5 beats/min; P < 0.001). A significant nocturnal decrease in SBP and DBP was observed both before (SBP; daytime, 129.1 +/- 2.8 vs. night time, 115.9 +/- 3.0 mmHg, P < 0.001 and DBP; daytime, 80.7 +/- 1.6 vs. night time, 69.2 +/- 1.8 mmHg, P < 0.001) and following GHR (SBP; daytime, 122.8 +/- 2.6 vs. night time, 110.0 +/- 3.6 mmHg, P < 0.001 and DBP; daytime, 73.9 +/- 1.8 vs. night time, 62.0 +/- 2.3 mmHg, P < 0.001). Individual and population-mean cosinor analysis demonstrated significant circadian rhythms for SBP, DBP and HR before and after 12 months on GHR (P < 0.001), suggesting that SBP, DBP and HR circadian rhythms were not altered by GHR. There was, however, a significant reduction in SBP (124.2 +/- 2.8 vs. 118.4 +/- 2.8 mmHg, P < 0.001) and DBP (77.0 +/- 1.6 vs. 70.2 +/- 1.8 mmHg, P < 0.001) MESOR with an increase in HR MESOR (68.9 +/- 2.5 vs. 72.2 +/- 2.4 beats/min, P < 0.01) following GHR. CONCLUSIONS: Systolic and diastolic BP and HR circadian rhythms are preserved in AGHD following 12 months of GHR. However, there is a significant decrease in 24-h mean SBP and DBP and increase in 24-h mean HR after 12 months on GHR. We postulate that this decrease in 24-h mean SBP and DBP may result in a reduction of cardiovascular morbidity and mortality and may explain the beneficial effects of GHR on cardiovascular system previously reported in AGHD patients.