Temporal structure of in vivo adrenal secretory activity estimated by deconvolution analysis

Circadian and ultradian rhythms of plasma cortisol concentrations have been documented under physiological conditions in diverse animal species. Using a novel, biophysical convolution model to remove subject-specific metabolic clearance rates, we have now estimated spontaneous adrenal secretory events in vivo. The latter were characterized by prominent ultradian rhythms of discrete secretory bursts with periodicities averaging 32, 46, 76, and 130 min. These ultradian cortisol secretory rhythms represented a 17- to 240-fold larger fraction of circadian secretory variations than did cortisol concentration rhythms. We conclude that deconvolution analysis can unmask underlying ultradian rhythms in adrenal secretory activity in vivo.     

A statistical model of diurnal variation in human growth hormone

The diurnal pattern of growth hormone (GH) serum levels depends on the frequency and amplitude of GH secretory events, the kinetics of GH infusion into and clearance from the circulation, and the feedback of GH on its secretion. We present a two-dimensional linear differential equation model based on these physiological principles to describe GH diurnal patterns. The model characterizes the onset times of the secretory events, the secretory event amplitudes, as well as the infusion, clearance, and feedback half-lives of GH. We illustrate the model by using maximum likelihood methods to fit it to GH measurements collected in 12 normal, healthy women during 8 h of scheduled sleep and a 16-h circadian constant-routine protocol. We assess the importance of the model components by using parameter standard error estimates and Akaike's Information Criterion. During sleep, both the median infusion and clearance half-life estimates were 13.8 min, and the median number of secretory events was 2. During the constant routine, the median infusion half-life estimate was 12.6 min, the median clearance half-life estimate was 11.7 min, and the median number of secretory events was 5. The infusion and clearance half-life estimates and the number of secretory events are consistent with current published reports. Our model gave an excellent fit to each GH data series. Our analysis paradigm suggests an approach to decomposing GH diurnal patterns that can be used to characterize the physiological properties of this hormone under normal and pathological conditions.     

Pulsatile ACTH secretion: variation with time of day and relationship to cortisol

It has long been known that ACTH is secreted in an episodic fashion demonstrating circadian and ultradian rhythms. High intensity venous sampling has recently revealed that in addition to these larger ultradian fluctuations in hormone levels, plasma ACTH in rats demonstrates high frequency, low amplitude oscillations which have been called "micropulses." These micropulses were not detected in previous studies due to sampling intervals of greater than 5 minutes. To investigate the presence of these ACTH micropulses in a primate species, blood samples were drawn from six chair-restrained rhesus monkeys at one-minute intervals for up to 70 minutes and plasma was assayed for immunoreactive ACTH. To assess the variation in ACTH micropulse parameters with time of day and the relationship to cortisol secretion, four of the monkeys were sampled for three 70-minute periods beginning at 0530, 1100, and 1730 hours, and plasma was assayed for immunoreactive ACTH and cortisol. Analysis of the data revealed that ACTH and cortisol are secreted in micropulses in rhesus monkeys with marked individual variation in the pattern of secretion and a concurrence of approximately 75% of ACTH and cortisol micropulses. Difference in pulse amplitude but not frequency appeared to contribute to the circadian variation in mean ACTH levels and a sampling interval of two minutes appeared to be adequate for accurately identifying micropulses of ACTH.     

Temporal characteristics of cortisol metabolism in adrenalectomized primates

The rhythmicities observed in the plasmatic levels of cortisol are generally attributed to rhythms of production and release of the hormone. Since the plasmatic concentration of any given substance is a function of its production and its removal from the circulation, it is conceivable that the metabolism of cortisol also occurs in an oscillating fashion. To test this hypothesis Rhesus monkeys were submitted to bilateral adrenalectomy; cortisol was replaced at a constant infusion rate while blood was sampled at hourly intervals for the measurement of cortisol plasma levels. Rhythmic oscillations in the cortisol levels were observed. These rhythms exhibited two major components: a circadian and an ultradian component. The authors suggest that these rhythms be considered whenever normal or pathologic hormone rhythmicities are analyzed.     

Circadian rhythms of salivary cortisol content during long-term space flight

Adaptation mechanisms of adrenal function related to secretion of cortisol were studied under conditions of microgravity. Parameters of diurnal rhythms of salivary cortisol were studied by Russian cosmonauts on board orbital station Mir during long-term space flights (SF). The preflight circadian rhythms of salivary cortisol in cosmonauts were characterized by the morning maximum occurring at 9∶43 a.m., the fluctuation amplitude 6.05 nmol/1, and the daily average concentration 8.79 nmol/l. The characteristics of cortisol diurnal rhythm changed under conditions of long-term space flight. On average, the rhythm measure and amplitude decreased after two months of flight. The postflight maximum concentration of free cortisol tended to occur later in the day. Evidently, the motor activity during SF, i.e., prophylactic exercises along with other factors, significantly influenced the parameters of cortisol circadian rhythm that was revealed by the individual variability of findings during the flight. After the long-term SF, individual ratios of salivary and plasma cortisol levels increased against the background of increased plasma content of the hormone, i.e., the fraction of free, physiologically active hormone in the total pool of circulating molecules decreased.     

Diurnal rhythms of free estradiol and cortisol during the normal menstrual cycle in women with major depression

To investigate whether depression is accompanied by changes in diurnal rhythms of free estradiol and cortisol in different phases of the menstrual cycle, we measured these two hormone levels in saliva samples collected every 2 h for 24 h from 15 healthy normally cycling women and 12 age-matched normally cycling women suffering from major depression taking antidepressants. The assessments were repeated four times over one menstrual cycle: during menstruation and in the late follicular/peri-ovulating, early to mid-luteal and late luteal phases, respectively. Quantification with a nonlinear periodic regression model revealed distinct diurnal rhythms in free estradiol and free cortisol in all subjects. For the diurnal cortisol rhythm, significant differences were found in the peak-width and ultradian amplitude among different menstrual phases, both in controls and depressed patients, while no significant differences were found between the two groups. The diurnal estradiol rhythm, on the other hand, was quite consistent among different menstrual phases within both groups, while the depressed patients had overall larger amplitudes than controls, which is negatively correlated with disease duration. Significant positive correlations between the two hormone rhythms were found for 24-h mean level (mesor), peak, and trough in late luteal phase, and for ultradian harmonics in early to mid-luteal phase in controls, but only for ultradian harmonics in late follicular/peri-ovulating phase and for acrophase in the menstruation phase in depressed patients. A sub-analysis was also performed in patients who received Fluoxetine (n = 7). The findings implicate a close correlation between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, both of which may be involved in depression.     

Rhythmic and Nonrhythmic Modes of Anterior Pituitary Gland Secretion

Because of confounding effects of subject-specific and hormone-specific metabolic clearance, the nature of anterior pituitary secretory events in vivo is difficult to ascertain. We review an approach to this problem, in which deconvolu-tion analysis is used to dissect the underlying secretory behavior of an endocrine gland quantitatively from available serial plasma hormone concentration measurements assuming one- or two-compartment elimination kinetics. This analytical tool allows one to ask the following physiological questions: (a) does the anterior pituitary gland secrete exclusively in randomly dispersed bursts, and/or does a tonic (constitutive) mode of interburst hormone secretion exist? and (b) what secretory mechanisms generate the circadian or nyctohemeral rhythms in blood concentrations of pituitary hormones? Waveform-independent deconvolution analysis of 24-h serum hormone concentration profiles of immunoreactive growth hormone (GH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and β-endorphin in normal men sampled every 10 min showed that (a) anterior pituitary gland secretion in vivo occurs in an exclusively burstlike mode for all hormones except TSH and prolactin (for the latter two, a mixed burst and basal mode pertains); (b) significant nyctohemeral regulation of secretory burst frequency alone is not demonstrable for any hormone; (c) prominent 24-h variations in secretory-burst amplitude alone are delineated for ACTH and LH; (d) TSH, GH, and β-endorphin are both frequency and amplitude controlled; (e) prolactin manifests 24-h rhythms in both secretory-burst amplitude and nadir secretory rates; (f) no significant diurnal variations occur in FSH secretory parameters; and (g) a fixed hormone half-life yields good fits of the 24-h serum hormone concentration series, which indicates that there is no need to introduce diurnal variations in hormone half-lives. In summary, the normal human anterior pituitary gland appears to release its various (glyco)protein hormones via intermittent secretory episodes that are apparently unassociated with significant basal hormone secretion, except in the case of TSH and prolactin. Hormone-specific amplitude and/or frequency control of secretory burst activity over 24 h provides the mechanistic basis for the classically recognized nyctohemeral rhythms in plasma concentrations of adenohypophyseal hormones in the human.     

Rhythmic and Nonrhythmic Modes of Anterior Pituitary Gland Secretion

Because of confounding effects of subject-specific and hormone-specific metabolic clearance, the nature of anterior pituitary secretory events in vivo is difficult to ascertain. We review an approach to this problem, in which deconvolu-tion analysis is used to dissect the underlying secretory behavior of an endocrine gland quantitatively from available serial plasma hormone concentration measurements assuming one- or two-compartment elimination kinetics. This analytical tool allows one to ask the following physiological questions: (a) does the anterior pituitary gland secrete exclusively in randomly dispersed bursts, and/or does a tonic (constitutive) mode of interburst hormone secretion exist? and (b) what secretory mechanisms generate the circadian or nyctohemeral rhythms in blood concentrations of pituitary hormones? Waveform-independent deconvolution analysis of 24-h serum hormone concentration profiles of immunoreactive growth hormone (GH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and β-endorphin in normal men sampled every 10 min showed that (a) anterior pituitary gland secretion in vivo occurs in an exclusively burstlike mode for all hormones except TSH and prolactin (for the latter two, a mixed burst and basal mode pertains); (b) significant nyctohemeral regulation of secretory burst frequency alone is not demonstrable for any hormone; (c) prominent 24-h variations in secretory-burst amplitude alone are delineated for ACTH and LH; (d) TSH, GH, and β-endorphin are both frequency and amplitude controlled; (e) prolactin manifests 24-h rhythms in both secretory-burst amplitude and nadir secretory rates; (f) no significant diurnal variations occur in FSH secretory parameters; and (g) a fixed hormone half-life yields good fits of the 24-h serum hormone concentration series, which indicates that there is no need to introduce diurnal variations in hormone half-lives. In summary, the normal human anterior pituitary gland appears to release its various (glyco)protein hormones via intermittent secretory episodes that are apparently unassociated with significant basal hormone secretion, except in the case of TSH and prolactin. Hormone-specific amplitude and/or frequency control of secretory burst activity over 24 h provides the mechanistic basis for the classically recognized nyctohemeral rhythms in plasma concentrations of adenohypophyseal hormones in the human.     

Characterizing the amplitude dynamics of the human core-temperature circadian rhythm using a stochastic-dynamic model

Two measures, amplitude and phase, have been used to describe the characteristics of the endogenous human circadian pacemaker, a biological clock located in the hypothalamus. Although many studies of change in circadian phase with respect to different stimuli have been conducted, the physiologic implications of the amplitude changes (dynamics) of the pacemaker are unknown. It is known that phase changes of the human circadian pacemaker have a significant impact on sleep timing and content, hormone secretion, subjective alertness and neurobehavioral performance. However, the changes in circadian amplitude with respect to different stimuli are less well documented. Although amplitude dynamics of the human circadian pacemaker are observed in physiological rhythms such as plasma cortisol, plasma melatonin and core temperature data, currently methods are not available to accurately characterize the amplitude dynamics from these rhythms. Of the three rhythms core temperature is the only reliable variable that can be monitored continuously in real time with a high sampling rate. To characterize the amplitude dynamics of the circadian pacemaker we propose a stochastic-dynamic model of core temperature data that contains both stochastic and dynamic characteristics. In this model the circadian component that has a dynamic characteristic is represented as a perturbation solution of the van der Pol equation and the thermoregulatory response in the data that has a stochastic characteristic is represented as a first-order autoregressive process. The model parameters are estimated using data with a maximum likelihood procedure and the goodness-of-fit measures along with the associated standard error of the estimated parameters provided inference about the amplitude dynamics of the pacemaker. Using this model we analysed core temperature data from an experiment designed to exhibit amplitude dynamics. We found that the circadian pacemaker recovers slowly to an equilibrium level following amplitude suppression. In humans this reaction to perturbation from equilibrium value has potential physiological implications.     

Twenty-four-hour secretory patterns of cortisol,progesterone and estradiol in heifers during the follicular and luteal phases of the ovarian cycle

Daily variations of plasma cortisol, progesterone and estradiol concentrations were measured by radioimmunoassay in six different normally cycling heifers during estrus (day 1 of the cycle) and diestrus (days 12–15 of the cycle). Each animal was fitted with an indwelling jugular catheter, and blood was withdrawn at 30-min intervals over a 24-h period. Statistical evaluation of the hormonal profiles using time series analysis revealed that all three steroids are secreted episodically with secretory episodes varying in number, magnitude and timing among different heifers. After dividing the 24-h into three 8-h time periods (I, 09.00–17.00 h; II. 17.00–01.00h; III, 01.00–09.00 h) a prominent circadian rhythm was found for cortisol during estrus and diestrus. Diurnal periodicity similar to that of cortisol was noticed for plasma progesterone during estrus but not diestrus when a functional corpus luteum was present. Estradiol secretion during the follicular and luteal phase of the estrous cycle was characterized by intermittent sustained elevations lasting about 9–15 h and marked by a graded rise and fall of hormone levels unrelated to photoperiod.From our results obtained in cycling heifers we conclude the following: (1) Plasma cortisol exhibits a distinct circadian rhythm during estrus and diestrus which is highly correlated with the light–dark cycle. (2) Plasma progesterone during estrus demonstrates a diurnal pattern which is absent in diestrous heifers bearing a corpus luteum. (3) Plasma estradiol lacks circadian rhythmicity but shows a distinct pattern different from that of progesterone, indicating that both steroids are secreted independently and not controlled by a circadian pacemaker.     

Circadian rhythm of cholesterol-7alpha-hydroxylase and cortisol in the African green monkey (Cercopithecus aethiops).

Cholesterol-7alpha-hydroxylase in African green monkey liver had an apparent Km of 1.65-10(-4) M cholesterol and a pH optimum of 7.4. The amplitudes of the circadian maxima of enzyme activity and serum cortisol levels were significantly greater in vervets than in grivets. Fluctuations in enzyme activity and cortisol levels during the circadian cycle were positively correlated (r = 0.89). Enzyme activities and hormone levels were 2.7-fold lower over a 24-h period in the grivet than in the vervet. Cholesterol feeding reduced the enzyme activity by 40% and serum cortisol was reduced to 38% of control levels at the diurnal peak. Serum glucocorticoids may be important physiological regulators of cholesterol-7alpha-hydroxylase in non-human primates. The concentration of cortisol and its time of release appear to be factors in the hyperresponsive trait of grivets. Genetic differences between vervet and grivet races may account for differences in the amplitude and timing of the circadian rhythm of cholesterol-7alpha-hydroxylase activity possibly influenced by cortisol.     

月经周期不同阶段游离皮质醇昼夜节律的变化

为了研究皮质醇分泌的昼夜节律在月经周期中的变化,实验对15位月经周期正常的育龄期健康妇女,在月经周期的不同阶段分别于24h内每隔两小时采样,检测唾液昼夜游离皮质醇水平。采用非线性回归分析模型分析皮质醇昼夜节律。结果显示,皮质醇昼夜节律在整个月经周期都具有复杂的明显受到亚节律(ultradian)影响的分泌形式;与月经期相比,围排卵期和黄体晚期昼夜节律波峰宽度(peak-width)明显减低(P=0．005与0．031),而昼夜节律波谷(trough)有抬高趋势(P=0．0622与0．066);黄体晚期的亚节律波幅(ultradian amplitude)与月经期相比显著减低(P=0．002)而与围排卵期相比有减低趋势(P=0．05)。这些结果提示月经周期的不同阶段对皮质醇分泌的昼夜节律有影响。     

Multiple Component Analysis of Plasma Growth Hormone in Children with Standard and Short Stature

Growth hormone (GH) concentrations (in ng/ml) were determined by radioimmunoassay, in plasma obtained at about 3-hr intervals during a 24-hr sampling span, from 42 boys and 12 girls of short stature (2-4 standard deviations below their peer group mean), and 13 boys and 9 girls of standard stature. Subjects had 11.20 0.37 years of age at the time of study, and were living on a diurnal waking (∼07:30 to ∼22:30), nocturnal resting routine during sampling. Analysis of these data by single and population-mean cosinor methods as well as by analysis of variance revealed circadian and ultradian prominent components characterizing most groups. Accordingly, a multiple component analysis was undertaken for data of each group separately, as well as for all subjects. A comparison of circadian parameters indicates similar characteristics between short and standard children, whether one compares boys [P=0.674, 0.371 and 0.749 for comparison of rhythm adjusted means (M), amplitudes (A) and acrophases (), respectively], girls (P=0.993,0.914 and 0.397), or all children (P=0.859,0.712 and 0.865). Differences are found, however, in circasemidian characteristics as well as in the prominent 8-hr ultradian component documented for the short but not for the standard children. These ultradian components should be taken into consideration in the design and later evaluation of a time-specified treatment of children of short stature.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish, Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish,Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

The minimal model of the hypothalamic–pituitary–adrenal axis

This paper concerns ODE modeling of the hypothalamic–pituitary– adrenal axis (HPA axis) using an analytical and numerical approach, combined with biological knowledge regarding physiological mechanisms and parameters. The three hormones, CRH, ACTH, and cortisol, which interact in the HPA axis are modeled as a system of three coupled, nonlinear differential equations. Experimental data shows the circadian as well as the ultradian rhythm. This paper focuses on the ultradian rhythm. The ultradian rhythm can mathematically be explained by oscillating solutions. Oscillating solutions to an ODE emerges from an unstable fixed point with complex eigenvalues with a positive real parts and a non-zero imaginary parts. The first part of the paper describes the general considerations to be obeyed for a mathematical model of the HPA axis. In this paper we only include the most widely accepted mechanisms that influence the dynamics of the HPA axis, i.e. a negative feedback from cortisol on CRH and ACTH. Therefore we term our model the minimal model. The minimal model, encompasses a wide class of different realizations, obeying only a few physiologically reasonable demands. The results include the existence of a trapping region guaranteeing that concentrations do not become negative or tend to infinity. Furthermore, this treatment guarantees the existence of a unique fixed point. A change in local stability of the fixed point, from stable to unstable, implies a Hopf bifurcation; thereby, oscillating solutions may emerge from the model. Sufficient criteria for local stability of the fixed point, and an easily applicable sufficient criteria guaranteeing global stability of the fixed point, is formulated. If the latter is fulfilled, ultradian rhythm is an impossible outcome of the minimal model and all realizations thereof. The second part of the paper concerns a specific realization of the minimal model in which feedback functions are built explicitly using receptor dynamics. Using physiologically reasonable parameter values, along with the results of the general case, it is demonstrated that un-physiological values of the parameters are needed in order to achieve local instability of the fixed point. Small changes in physiologically relevant parameters cause the system to be globally stable using the analytical criteria. All simulations show a globally stable fixed point, ruling out periodic solutions even when an investigation of the ‘worst case parameters’ is performed.     

Modeling the glucose-insulin regulatory system and ultradian insulin secretory oscillations with two explicit time delays

In the glucose-insulin regulatory system, ultradian insulin secretory oscillations are observed to have a period of 50-150 min. After pioneering work traced back to the 1960s, several mathematical models have been proposed during the last decade to model these ultradian oscillations as well as the metabolic system producing them. These currently existing models still lack some of the key physiological aspects of the glucose-insulin system. Applying the mass conservation law, we introduce two explicit time delays and propose a more robust alternative model for better understanding the glucose-insulin endocrine metabolic regulatory system and the ultradian insulin secretory oscillations for the cases of continuous enteral nutrition and constant glucose infusion. We compare the simulation profiles obtained from this two time delay model with those from the other existing models. As a result, we notice many unique features of this two delay model. Based on our intensive simulations, we suspect that one of the possibly many causes of ultradian insulin secretion oscillations is the time delay of the insulin secretion stimulated by the elevated glucose concentration.     

Deconvolution of Serum Cortisol Levels by Using Compressed Sensing

The pulsatile release of cortisol from the adrenal glands is controlled by a hierarchical system that involves corticotropin releasing hormone (CRH) from the hypothalamus, adrenocorticotropin hormone (ACTH) from the pituitary, and cortisol from the adrenal glands. Determining the number, timing, and amplitude of the cortisol secretory events and recovering the infusion and clearance rates from serial measurements of serum cortisol levels is a challenging problem. Despite many years of work on this problem, a complete satisfactory solution has been elusive. We formulate this question as a non-convex optimization problem, and solve it using a coordinate descent algorithm that has a principled combination of (i) compressed sensing for recovering the amplitude and timing of the secretory events, and (ii) generalized cross validation for choosing the regularization parameter. Using only the observed serum cortisol levels, we model cortisol secretion from the adrenal glands using a second-order linear differential equation with pulsatile inputs that represent cortisol pulses released in response to pulses of ACTH. Using our algorithm and the assumption that the number of pulses is between 15 to 22 pulses over 24 hours, we successfully deconvolve both simulated datasets and actual 24-hr serum cortisol datasets sampled every 10 minutes from 10 healthy women. Assuming a one-minute resolution for the secretory events, we obtain physiologically plausible timings and amplitudes of each cortisol secretory event with R ² above 0.92. Identification of the amplitude and timing of pulsatile hormone release allows (i) quantifying of normal and abnormal secretion patterns towards the goal of understanding pathological neuroendocrine states, and (ii) potentially designing optimal approaches for treating hormonal disorders.     

Circadian rhythms of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), cortisol, and melatonin in women with breast cancer

Background: Circadian rhythms in plasma concentrations of many hormones and cytokines determine their effects on target cells. Methods: Circadian variations were studied in cortisol, melatonin, cytokines (basic fibroblast growth factor [bFGF], EGF, insulin-like growth factor-1 [IGF-1]), and a cytokine receptor (insulin-like growth factor binding protein-3 [IGFBP-3]) in the plasma of 28 patients with metastatic breast cancer. All patients followed a diurnal activity pattern. Blood was drawn at 3h intervals during waking hours and once during the night, at 03:00. The plasma levels obtained by enzyme-linked immunoassay (ELISA) or radioimmunoassay (RIA) were evaluated by population mean cosinor (using local midnight as the phase reference and by one-way analysis of variance (ANOVA). Results: Cortisol and melatonin showed a high-amplitude circadian rhythm and a superimposed 12h frequency. bFGF showed a circadian rhythm with an acrophase around 13:00 with a peak-to-trough interval (double amplitude) of 18.2% and a superimposed 12h frequency. EGF showed a circadian rhythm with an acrophase around 14:20, a peak-to-trough interval of 25.8%, and a superimposed 12h frequency. IGF-1 showed a high value in the morning, which is statistically different t test) from the low value at 10:00, but a regular circadian or ultradian rhythm was not recognizable as a group phenomenon. IGFBP-3 showed a low-amplitude (peak-to-trough difference 8.4%) circadian rhythm with the acrophase around 11:00 and low values during the night. Conclusions: (1) Circadian periodicity is maintained in hospitalized patients with metastatic breast cancer. (2) Ultradian (12h) variations were superimposed on the circadian rhythms of the hormones and several of the cytokines measured. (3) Studies of hormones and cytokines in cancer patients have to take their biologic rhythms into consideration. (4) The circadian periodicity of tumor growth stimulating or restraining factors raises questions about circadian and/ or ultradian variations in the pathophysiology of breast cancer. (Chronobiology International, 18(4), 709-727)     

A method to evaluate dynamics and periodicity of hormone secretion

Spontaneous hormone secretory dynamics include tonic and pulsatile components and a number of periodic processes. Circadian variations are usually found for melatonin, TSH and GH, with peak secretions at night, and in cortisol secretion, which peaks in the morning. Free thyroxine (FT4) and insulin-like growth factor (IGF)1 levels do not always change with circadian rhythmicity or show only minor fluctuations. Fractional variations explore the dynamics of secretion related to time intervals, and the rate of change in serum levels represents a signal for the receptorial system and the target organ. We evaluated time-related variations and change dynamics for melatonin, cortisol, TSH, FT4, GH and IGF1 levels in blood samples obtained every 4 h for 24 h from eleven healthy males, ages 35-53 years (mean ? SE 43.6 ± 1.7). Nyctohemeral (i.e., day-night) patterns of hormone secretion levels and the fractional rate of variation between consecutive 4-hourly time-qualified hormone serum levels (calculated as percent change from time 1 to time 2) were evaluated for circadian periodicity using a 24 and 12-h cosine model. A circadian rhythm was validated for serum level changes in cortisol with peaks of the 24-h cosine model at 07:48 h, and melatonin, TSH and GH, with phases at 01:35 h, 23:32 h, and 00:00 h, respectively. A weak, but significant, 12-h periodicity was found for FT4 serum levels, with minor peaks in the morning (10:00 h) and evening (22:00 h), and for IGF1, with minor peaks in the morning (07:40 h) and evening (19:40 h). Circadian rhythmicity was found in the 4-hourly fractional variations with phases of increase or surge at 02:00 h for cortisol, 22:29 h for melatonin, 05:14 h for FT4, and 21:19 h for GH. A significant 12-h periodicity was found for the 4-hourly fractional variations of TSH with two peaks in the morning (decrease or drop at 04:42 h) and afternoon (surge at 16:28 h), whereas IGF1 fractional variation changes did not show a significant rhythmic pattern. In conclusion, the calculation of the time-qualified fractional rate of variation allows evaluation of the dynamics of secretion and the specification of the timepoint(s) of maximal change of secretion, not only for hormones whose secretion is characterized by a circadian pattern of variation, but also for hormones that show no circadian or only weak ultradian (12 h) variations (i.e., FT4).