Diurnal cortisol changes in newborn infants suggesting entrainment of peripheral circadian clock in utero and at birth

Predicting iatrogenic adrenal insufficiency in neonates exposed to prolonged steroid courses: do cortisol levels help?

OBJECTIVE

To determine whether random cortisol levels obtained in neonates to assess for secondary adrenal insufficiency (AI) after prolonged steroid exposure are predictive of central AI.

STUDY DESIGN

Data were collected on neonates born 2017-2022 who received ≥10 consecutive days of systemic steroids and had cortisol measured thereafter. Data were then collected on whether those neonates developed signs of AI or had a failed adrenocorticotropic hormone (ACTH) stimulation test.

RESULTS

Of the 71 cortisol levels (in 67 neonates) that were analyzed, there was no difference in cortisol levels between neonates who developed AI (median cortisol level of 6.5 mcg/dl) and those who did not (median of 9.2 mcg/dl), or between those who failed their ACTH stimulation test or passed it, using Wilcoxon ranked sum tests.

CONCLUSION

These findings demonstrate that cortisol levels may not be helpful in identifying AI in neonates exposed to prolonged steroids.

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Effects of a tripartite intervention on biological stress in preterm infants during heel pricks for newborn screening: A randomized controlled trial

This prospective randomized trial examined the effects of a tripartite intervention (behavioral state modulation + nonnutritive sucking + tucking) on stress from procedural pain during heel pricks. Blood samples for routine screening were collected by heel pricks 48 h after birth (Stage 1) and at ≥37 weeks' gestation (Stage 2); salivary cortisol levels (SCLs) pre-prick (T0) and 20 min post-prick (T1) assessed stress. Preterm infants (n = 64) sampled by convenience at Level III neonatal care units were randomly assigned to the control condition (usual care) or intervention condition (tripartite intervention). Generalized estimating equations examined differences in salivary cortisol between conditions. After adjusting for effects of gestational age, postmenstrual age, and baseline SCLs, (1) at Stage 1, the change in salivary cortisol from T0 to T1 in preterm infants who received the tripartite intervention was, on average, significantly lower by 0.431 units (log scale) than the change in preterm infants who received the control condition (p < 0.001); (2) in the tripartite intervention condition, the difference between the change in mean SCLs from T0 to T1 at Stages 1 and 2 was significantly lower by 0.287 units (log scale), on average than between the change at Stages 1 and 2 in the control condition (p = 0.026). The provision of a tripartite intervention during heel prick significantly decreased the raise of SCLs compared with infants receiving usual care, suggesting lower stress. Clinicians could easily implement the tripartite intervention for heel-stick support; however, replication is needed before recommending its incorporation into routine heel stick and other stressful procedures.

Promoting sound development of preterm infants in the name of developmental neuroscience: Beyond advanced life support and neuroprotection

Despite the increased survival opportunities for extremely preterm infants, their long-term cognitive outcomes remain poor, with increased incidence of cognitive impairments in childhood and reduced opportunities to attend higher education in young adulthood compared to their term-born peers. Given that a considerable fraction of preterm infants develop cognitive impairments even without apparent sentinel events at birth and cerebral lesions on MRI assessed at term equivalent age, future strategies to improve the outcome may need to address cerebral dysfunction, which cannot be explained by the classical understanding of the injury cascade triggered by hypoxia-ischaemia around birth. Developmental care has been proposed to minimize neurodevelopmental impairments related to preterm birth. However, considerable modes of cares, environmental settings and procedures provided by the developmental care of current style appear to offer little benefit to the sound development of infants. Although it is obvious that advanced life support and neuroprotective treatments fall far short in compensating for the burden of preterm birth, researchers need to make further effort to fill the knowledge gap in the cerebral function of foetuses and newborn infants before establishing evidence-based developmental care. Clinicians need to develop an ability to translate the findings from basic and translational studies incorporating their potential biases and limitations. Care for newborn infants needs to be reassessed, including but not limited to developmental care, in the context that any sensory input and motor reaction of preterm infants may ultimately affect their cognitive functioning.

Postnatal steroid management in preterm infants with evolving bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease commonly affecting extremely preterm infants. Although mechanical ventilation and oxygen requirements in premature infants are identified as inciting mechanisms for inflammation and the development of BPD over time, data now support an array of perinatal events that may stimulate the inflammatory cascade prior to delivery. Corticosteroids, such as dexamethasone and hydrocortisone, have proven beneficial for the prevention and management of BPD postnatally due to their anti-inflammatory characteristics. This review aims to examine the pharmacologic properties of several corticosteroids, appraise the existing evidence for postnatal corticosteroid use in preterm infants, and assess steroid management strategies to ameliorate BPD. Finally, we aim to provide guidance based on clinical experience for managing adrenal suppression resulting from prolonged steroid exposure since this is an area less well-studied.

Circadian Rhythms of Perineuronal Net Composition

Perineuronal nets (PNNs) are extracellular matrix (ECM) structures that envelop neurons and regulate synaptic functions. Long thought to be stable structures, PNNs have been recently shown to respond dynamically during learning, potentially regulating the formation of new synapses. We postulated that PNNs vary during sleep, a period of active synaptic modification. Notably, PNN components are cleaved by matrix proteases such as the protease cathepsin-S. This protease is diurnally expressed in the mouse cortex, coinciding with dendritic spine density rhythms. Thus, cathepsin-S may contribute to PNN remodeling during sleep, mediating synaptic reorganization. These studies were designed to test the hypothesis that PNN numbers vary in a diurnal manner in the rodent and human brain, as well as in a circadian manner in the rodent brain, and that these rhythms are disrupted by sleep deprivation. In mice, we observed diurnal and circadian rhythms of PNNs labeled with the lectin Wisteria floribunda agglutinin (WFA+ PNNs) in several brain regions involved in emotional memory processing. Sleep deprivation prevented the daytime decrease of WFA+ PNNs and enhances fear memory extinction. Diurnal rhythms of cathepsin-S expression in microglia were observed in the same brain regions, opposite to PNN rhythms. Finally, incubation of mouse sections with cathepsin-S eliminated PNN labeling. In humans, WFA+ PNNs showed a diurnal rhythm in the amygdala and thalamic reticular nucleus (TRN). Our results demonstrate that PNNs vary in a circadian manner and this is disrupted by sleep deprivation. We suggest that rhythmic modification of PNNs may contribute to memory consolidation during sleep.

Biphasic Glucocorticoid Rhythm in One-Month-Old Infants: Reflection of a Developing HPA-Axis?

CONTEXT

The hypothalamus-pituitary-adrenal (HPA) axis displays a diurnal rhythm. However, little is known about its development in early life.

OBJECTIVE

To describe HPA-axis activity and study possible influencing factors in 1-month-old infants.

DESIGN

Observational.

SETTING

Amsterdam University Medical Center, location VU University Medical Center (VUMC), and Onze Lieve Vrouwe Gasthuis (OLVG), Amsterdam.

PARTICIPANTS

Fifty-five mother-infant pairs.

INTERVENTIONS

Collection of breast milk and infants' saliva 1 month postpartum for analysis of glucocorticoids (GCs; ie, cortisol and cortisone) using liquid chromatography- tandem mass spectrometry.

MAIN OUTCOME MEASURE

GC rhythm in infants' saliva and associations with vulnerability for maternal psychological distress (increased Hospital Anxiety and Depression Scale [HADS] score) or consultation at the Psychiatric Obstetric Pediatric (POP clinic), season at sampling, sex, and breast milk GC rhythmicity analyzed with SigmaPlot 14.0 software (Systat Software, San Jose, CA, USA) and regression analyses.

RESULTS

A significant biphasic GC rhythm was detected in infants, with mean peaks [standard error of the mean, SEM] at 6:53 am [1:01] and 18:36 pm [1:49] for cortisol, and at 8:50 am [1:11] and 19:57 pm [1:13] for cortisone. HADS score, POP consultation, season at sampling, and sex were not associated with the infants' GC rhythm. Breast milk cortisol maximum was positively associated with infants' cortisol area-under-the-curve (AUC) increase and maximum. Higher breast milk cortisone AUC increase, AUC ground, and maximum were associated with an earlier maximum in infants. Breast milk and infant GC concentrations were associated between 6:00 am and 9:00 am.

CONCLUSIONS

A biphasic GC rhythm, peaking in the morning and evening, was seen in 1-month-old infants at a group level. Breast milk GC parameters might be associated with the infants' GC rhythm, possibly caused by a signaling effect of breast milk GCs, or as an associative effect of increased mother-infant synchrony. These results contribute to an increased understanding of early life HPA-axis development.

Circadian Clock, Time-Restricted Feeding and Reproduction

The goal of this review was to seek a better understanding of the function and differential expression of circadian clock genes during the reproductive process. Through a discussion of how the circadian clock is involved in these steps, the identification of new clinical targets for sleep disorder-related diseases, such as reproductive failure, will be elucidated. Here, we focus on recent research findings regarding circadian clock regulation within the reproductive system, shedding new light on circadian rhythm-related problems in women. Discussions on the roles that circadian clock plays in these reproductive processes will help identify new clinical targets for such sleep disorder-related diseases.

Clinical utility of stimulation tests in infants with suspected adrenal insufficiency (AI)

Diagnosis of adrenal insufficiency (AI) in infants can be difficult. While a low random cortisol can signal AI, often confirmatory tests are required when clinical suspicion is strong but the cortisol levels are equivocal. Several studies have demonstrated that in sick preterm infants, there is relative adrenal insufficiency (RAI) defined as an inadequate cortisol production relative to the degree of stress or illness, a condition which can last for several weeks, while in term infants the adrenal axis is mature at birth (Bagnoli F, Mori A, Fommei C, Coriolani G, Badii S, et al. ACTH and cortisol cord plasma concentrations in preterm and term infants. J Perinatol 2013;33:520-4). Adrenocorticotrophic hormone (ACTH) and corticotrophin releasing hormone (CRH) stimulation tests have been validated in infants in several studies. In light of recent reports of false-negative results of stimulation tests, it is imperative to highlight the pitfalls of these tests. The purpose of this communication is to bring attention to the accuracy of timing of these tests in infants.

Feeding-Induced Cortisol Response in Newborn Infants

CONTEXT

Understanding the biological rhythms and stress response in sick newborns is important to minimize the negative effects of intensive care. Salivary cortisol has been used as a noninvasive surrogate marker of adrenal function; however, understanding of its control variables is insufficient.

OBJECTIVE

To investigate the presence of feeding-induced cortisol response and its control variables in newborns.

DESIGN, SETTING, AND PATIENTS

Fifty-three newborn infants, who were between 30 and 40 weeks' corrected age and were on 3-hourly regular oral/enteral feeding, were recruited between January 2013 and June 2014.

MAIN OUTCOME MEASURE

Saliva samples were collected before and 1 hour after regular feeding. Dependence of cortisol levels (adjusted for postnatal age) and their feeding-related elevation on clinical variables was assessed by using generalized estimating equations.

RESULTS

Higher cortisol levels were associated with corrected age ≥37 weeks and saliva samples collected after feeding (both P < 0.001). Oral feeding was associated with a greater feeding-induced cortisol response compared with exclusive enteral feeding (P = 0.034), whereas a prolonged feeding duration (≥30 minutes) was associated with a reduced cortisol response compared with brief feeding (<30 minutes) (P < 0.001). Gestational age, corrected age, antenatal/postnatal glucocorticoids, type of milk, and daily feeding volume had no effect on cortisol response.

CONCLUSIONS

Feeding-induced cortisol response was observed in newborns. The cortisol response was more prominent following oral feeding and was reduced with prolonged feeding. Future studies may investigate whether feeding-induced cortisol response plays a role in the acquisition of adrenal ultradian and diurnal rhythms.

Glucocorticoid metabolites in newborns: A marker for traffic noise related stress?

BACKGROUND

Traffic noise has been associated with an increased risk for several non-auditory health effects, which may be explained by a noise-induced release of stress hormones (e.g. glucocorticoids). Although several studies in children and adults have indicated an increased secretion of glucocorticoids after exposure to noise, information regarding newborns is scarce.

OBJECTIVES

To investigate the association between residential exposure to road traffic noise and postnatal stress response, as assessed by the concentration of glucocorticoids at five weeks of age.

METHODS

Residential noise exposure was estimated for each infant based on spatially detailed modeled data. Adjusted multivariable linear regression models were used to estimate the association between noise exposure and the concentration of nine glucocorticoid metabolites measured in urine of 165 infants from a prospective birth cohort in Bern, Switzerland. Noise exposure (Lden, dB) was categorized into tertiles: low (reference), medium and high.

RESULTS

Indications of a positive association were found between high road traffic noise and cortisol (% change relative to the reference: 12.1% [95% confidence interval: -10.3, 40.1%]) and cortisone (22.6% [-1.8, 53.0%]), but just the latter was borderline significant. Borderline significant associations were also found between downstream metabolites and higher road traffic noise levels; associations were found to be both positive (i.e. for β-cortolone (51.5% [-0.9, 131.5%])) and negative (i.e. for α-cortolone (-18.3% [-33.6, 0.6%]) and tetrahydrocortisol (-23.7% [-42.8, 1.9%])).

CONCLUSIONS

Our findings suggest a potential association between exposure to higher road traffic noise levels and changes in glucocorticoid metabolism in early postnatal life. A possible physiological relevance and associations with short- and long-term adverse health effects in a larger study population need to be further investigated.

Rhythmic Three-Part Harmony: The Complex Interaction of Maternal, Placental and Fetal Circadian Systems

From the perspective of circadian biology, mammalian pregnancy presents an unusual biological scenario in which an entire circadian system (i.e., that of the fetus) is embodied within another (i.e., that of the mother). Moreover, both systems are likely to be influenced at their interface by a third player, the placenta. Successful pregnancy requires major adaptations in maternal physiology, many of which involve circadian changes that support the high metabolic demands of the growing fetus. A functional role for maternal circadian adaptations is implied by the effects of circadian disruption, which result in pregnancy complications including higher risks for miscarriage, preterm labor, and low birth weight. Various aspects of fetal physiology lead to circadian variation, at least in late gestation, but it remains unclear what drives this rhythmicity. It likely involves contributions from the maternal environment and possibly from the placenta and the developing intrinsic molecular clocks within fetal tissues. The role of the placenta is of particular significance because it serves not only to relay signals about the external environment (via the mother) but may also exhibit its own circadian rhythmicity. This review considers how the fetus may be influenced by dynamic circadian signals from the mother and the placenta during gestation, and how, in the face of these changing influences, a new fetal circadian system emerges. Particular emphasis is placed on the role of endocrine signals, most notably melatonin and glucocorticoids, as mediators of maternal-fetal circadian interactions, and on the expression of the clock gene in the 3 compartments. Further study is required to understand how the mother, placenta, and fetus interact across pregnancy to optimize circadian adaptations that support adequate growth and development of the fetus and its transition to postnatal life in a circadian environment.

Dependence of nighttime sleep duration in one-month-old infants on alterations in natural and artificial photoperiod

Human sleep–wake cycles are entrained by both natural and artificial light–dark cycles. However, little is known regarding when and how the photoperiod changes entrain the biological clock after conception. To investigate the dependence of sleep patterns in young infants on the natural and artificial light–dark cycles, 1,302 pairs of one-month-old infants and their mothers were asked to answer a questionnaire. Birth in spring, longer daytime sleep duration, early/regular light-off times, and longer maternal nighttime sleep duration were identified as independent variables for longer infant nighttime sleep duration in both univariate and multivariate analyses. Longer maternal nighttime sleep duration was dependent on shorter naps and early/regular bed times but not on the season. We found that nighttime sleep duration depended on both natural and artificial diurnal photoperiod changes in one-month-old infants. Although sleep patterns of infants mimicked those of their mothers, nighttime sleep duration depended on the season, and was positively associated with daytime sleep duration, only in the infants. These specific variables, which render sleep patterns of the infants different from those of their mothers, might be a clue to reveal the covert acquisition process of mature circadian rhythms after birth.

Decreased Numbers of Somatostatin-Expressing Neurons in the Amygdala of Subjects With Bipolar Disorder or Schizophrenia: Relationship to Circadian Rhythms

BACKGROUND

Growing evidence points to a key role for somatostatin (SST) in schizophrenia (SZ) and bipolar disorder (BD). In the amygdala, neurons expressing SST play an important role in the regulation of anxiety, which is often comorbid in these disorders. We tested the hypothesis that SST-immunoreactive (IR) neurons are decreased in the amygdala of subjects with SZ and BD. Evidence for circadian SST expression in the amygdala and disrupted circadian rhythms and rhythmic peaks of anxiety in BD suggest a disruption of rhythmic expression of SST in this disorder.

METHODS

Amygdala sections from 12 SZ, 15 BD, and 15 control subjects were processed for immunocytochemistry for SST and neuropeptide Y, a neuropeptide partially coexpressed in SST-IR neurons. Total numbers (Nt) of IR neurons were measured. Time of death was used to test associations with circadian rhythms.

RESULTS

SST-IR neurons were decreased in the lateral amygdala nucleus in BD (Nt, p = .003) and SZ (Nt, p = .02). In normal control subjects, Nt of SST-IR neurons varied according to time of death. This pattern was altered in BD subjects, characterized by decreases of SST-IR neurons selectively in subjects with time of death corresponding to the day (6:00 am to 5:59 pm). Numbers of neuropeptide Y-IR neurons were not affected.

CONCLUSIONS

Decreased SST-IR neurons in the amygdala of patients with SZ and BD, interpreted here as decreased SST expression, may disrupt responses to fear and anxiety regulation in these individuals. In BD, our findings raise the possibility that morning peaks of anxiety depend on a disruption of circadian regulation of SST expression in the amygdala.

Is physiological glucocorticoid replacement important in children?

Cortisol has a distinct circadian rhythm with low concentrations at night, rising in the early hours of the morning, peaking on waking and declining over the day to low concentrations in the evening. Loss of this circadian rhythm, as seen in jetlag and shift work, is associated with fatigue in the short term and diabetes and obesity in the medium to long term. Patients with adrenal insufficiency on current glucocorticoid replacement with hydrocortisone have unphysiological cortisol concentrations being low on waking and high after each dose of hydrocortisone. Patients with adrenal insufficiency complain of fatigue, a poor quality of life and there is evidence of poor health outcomes including obesity potentially related to glucocorticoid replacement. New technologies are being developed that deliver more physiological glucocorticoid replacement including hydrocortisone by subcutaneous pump, Plenadren, a once-daily modified-release hydrocortisone and Chronocort, a delayed and sustained absorption hydrocortisone formulation that replicates the overnight profile of cortisol. In this review, we summarise the evidence regarding physiological glucocorticoid replacement with a focus on relevance to paediatrics.

Paradoxical diurnal cortisol changes in neonates suggesting preservation of foetal adrenal rhythms

Studies suggested the presence of foetal adrenal rhythms of cortisol, which are entrained in antiphase to maternal rhythms. In contrast, neonates are thought to have no adrenal rhythm until 2-3 months after birth. To test the hypothesis that a foetal-type adrenal rhythm is preserved after birth, saliva samples were collected from 65 preterm/term infants during hospital stay (30-40 weeks corrected age) at 10:00 and 19:00 h. Cortisol levels were assessed for their diurnal difference and dependence on antenatal/postnatal clinical variables. Cortisol levels were lower during periods 15-28 days and >28 days than ≤5 days of life. Lower cortisol was associated with pregnancy-induced hypertension (PIH), gestational age <28 weeks, and mechanical ventilation after birth. Higher cortisol was associated with vaginal delivery and non-invasive ventilation support at saliva collection. PIH and non-invasive mechanical ventilation at saliva collection were associated with cortisol levels even after adjustment for postnatal age. Cortisol levels were higher in the evening than in the morning, which was unassociated with gestational and postnatal age. Higher cortisol levels in the evening suggest the preservation of a foetal-type diurnal rhythm. Cortisol levels are associated with intrinsic and extrinsic variables, such as PIH, delivery mode, gestational age, and respiratory conditions.

Evidence for central hypercortisolism and elevated blood pressure in adolescent offspring of mothers with pre-eclampsia

OBJECTIVE

Maternal total and free cortisol concentrations are reduced in pre-eclampsia (PE) and gestational hypertension (GH). However, the effect of this on the hypothalamic-pituitary-adrenal (HPA) axis function in the offspring is unknown. We examined the basal HPA axis activity in adolescent offspring of mothers with pre-pregnancy hypertension/GH/PE.

DESIGN AND SUBJECTS

A total of 1182 participants (mean age 17·1 years) recruited from the Western Australian Pregnancy Cohort (Raine) Study provided fasting morning blood samples for basal HPA axis and concomitant clinical assessments, including blood pressure.

MEASUREMENTS

Plasma ACTH, total cortisol, corticosteroid-binding globulin (CBG) and free cortisol calculated by Coolens' equation were measured from the blood samples collected at home before 10:00 am.

RESULTS

Total plasma cortisol (689 ± 153 nmol/l vs 583 ± 172 nmol/l, P = 0·024), ACTH (15·5 ± 13 pmol/l vs 10·8 ± 5·1 pmol/l, P = 0·040) and calculated free cortisol (52 ± 21 nmol/l vs 42 ± 22 nmol/l, P = 0·052) were higher in the PE offspring than in controls. The pre-pregnancy hypertension group had evidence of a lower ACTH/plasma free cortisol ratio (0·22 vs 0·33 P = 0·020) and lower CBG (713 nmol/l vs 821 nmol/l, P = 0·004) compared with controls. Systolic blood pressure was elevated in the GH/PE group compared with controls (120 mmHg vs 116 mmHg, P = 0·006).

CONCLUSIONS

Hypothalamic-pituitary-adrenal axis activity is increased in the adolescent offspring of mothers with pre-eclampsia. This may be an adaptation resulting from the reduced maternal cortisol during foetal life. The resulting mild hypercortisolism may have implications for long-term health outcomes and warrants further investigation.

Comparison of cortisol samples in the first two weeks of life in preterm infants

BACKGROUND

Growing literature on negative childhood stress emphasizes the need to understand cortisol values from varying biomarker samples.

OBJECTIVE

This work aimed to examine cortisol samples for usability, associations, and individual stability in neonates.

SUBJECTS

The sample consisted of preterm infants (n=31).

MATERIALS AND METHODS

Analyses on cortisol collected from cord blood and from saliva and urine samples on days 1, 7, and 14 included Spearman correlations and paired t-tests.

RESULTS

Usability rates were 80.6% (cord blood), 85.9% (saliva), and 93.5% (urine). Salivary and urinary cortisol levels had significant correlation on day 1 only (p=0.004). Significant differences in individual stability of cortisol concentrations existed except in urine on days 1 and 7 and in saliva on days 7 and 14.

CONCLUSIONS

Usability was highest for urine samples. We found little correlation between cortisol sample levels at each time; individual stability of cortisol concentrations was minimal. Interpretation of cortisol findings in all studies should be performed cautiously.

Theory of Inpatient Circadian Care (TICC): A Proposal for a Middle-Range Theory

The circadian system controls the daily rhythms of a variety of physiological processes. Most organisms show physiological, metabolic and behavioral rhythms that are coupled to environmental signals. In humans, the main synchronizer is the light/dark cycle, although non-photic cues such as food availability, noise, and work schedules are also involved. In a continuously operating hospital, the lack of rhythmicity in these elements can alter the patient’s biological rhythms and resilience. This paper presents a Theory of Inpatient Circadian Care (TICC) grounded in circadian principles. We conducted a literature search on biological rhythms, chronobiology, nursing care, and middle-range theories in the databases PubMed, SciELO Public Health, and Google Scholar. The search was performed considering a period of 6 decades from 1950 to 2013. Information was analyzed to look for links between chronobiology concepts and characteristics of inpatient care. TICC aims to integrate multidisciplinary knowledge of biomedical sciences and apply it to clinical practice in a formal way. The conceptual points of this theory are supported by abundant literature related to disease and altered biological rhythms. Our theory will be able to enrich current and future professional practice.

Influence of acoustic stimulation on the circadian and ultradian rhythm of premature infants

The aim of the present study was to evaluate the development of the circadian rhythm of the salivary cortisol in premature infants and its correlation with the onset of the sleep-activity behavior pattern during the first 3 weeks of life under controlled light:dark conditions. Furthermore, we investigated the influence of acoustic stimulation by audiotaped lullabies or the maternal voice on the cortisol values and long-term sleep-activity patterns. The study was a block-randomized, prospective clinical trial with a study population of 62 preterm neonates (30<37 gestational age). We compared two study groups who listened either to music or to the maternal voice (music: N=20; maternal voice: N=20) with a matched control group (N=22). The acoustic stimulation took place every evening between 20:00 and 21:00 h for 30 min over a period of 2 weeks. The cortisol values and activity-rest behavior of the neonates were determined during the first 3 weeks of life on the 1st, 7th and 14th day. Actigraphic monitoring was used to record the activity pattern continuously over 24 h and a validated algorithm for neonates was used to estimate sleep and wakefulness. The saliva samples were obtained 10 min before and 10 min after the acoustic interventions for the study groups. Additionally, saliva samples were obtained from the control group seven times over a 24-h period (20:00, 21:00, 01:00, 05:00, 08:00, 13:00 and 17:00 h). The cortisol data were analyzed by fast Fourier transformation to assess periodic characteristics and frequencies. Hierarchical linear modeling was further performed for the statistical analysis.

RESULTS

The cortisol rhythm analysis indicated a circadian rhythm pattern for only one premature infant, all others of the neonates showed no circadian or ultradian rhythm in cortisol. Cortisol level of the premature neonates was significantly higher during the first day of the study period at night-time (median: 17.1 nmol/L, IQR=9.7-24.4 nmol/L) than on days 7 (median: 9.6 nmol/L, IQR=4.7-14.6 nmol/L; Tukey-HSD, z=4.12, p<0.001) and 14 (IQR=5.8-13.7 nmol/L; Tukey-HSD, z=2.89, p<0.05). No significant effect of acoustic stimulation was observed on the cortisol concentration and sleep-wake behavior. The activity-sleep rhythm of preterm neonates was dominated by ultradian rhythm patterns with a prominent period length of 4 h (30.5%). Activity frequencies of neonates were also significantly higher overnight on the first study day (mean: 329±185.1 U) than of night seven (mean: 260.2±132.4 U; Tukey-HSD, z=2.50, p<0.05). Quiet-activity patterns increased, whereas high-activity patterns decreased during the observation period. Average sleep time increased significantly during the study time from day 1 to day 7 (Tukey-HSD, z=2.51, p<0.05). In conclusion, premature infants showed higher cortisol levels - without a circadian rhythmicity - and higher activity frequencies in the first days after birth which may reflect an adaptation process of neonates after birth. Cortisol concentrations and the activity patterns were not influenced by music interventions.

Population pharmacokinetics of unbound hydrocortisone in critically ill neonates and infants with vasopressor-resistant hypotension

OBJECTIVES

To determine the population pharmacokinetics of unbound hydrocortisone in critically ill neonates and infants receiving IV hydrocortisone for treatment of vasopressor-resistant hypotension and to identify patient-specific sources of pharmacokinetic variability.

DESIGN

Prospective observational cohort study.

SETTING

Level 3 neonatal ICU.

PATIENTS

Sixty-two critically ill neonates and infants receiving IV hydrocortisone as part of standard of care for the treatment of vasopressor-resistant hypotension: median gestational age 28 weeks (range, 23-41), median weight 1.2 kg (range, 0.5-4.4), and 29 females.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Unbound baseline cortisol and postdose hydrocortisone concentrations measured from blood samples being drawn for routine laboratory tests. A one-compartment model best described the data. Allometric weight and postmenstrual age were significant covariates on unbound hydrocortisone clearance and volume of distribution. Final population estimates for clearance, volume of distribution, and baseline cortisol concentration were 20.2 L/hr, 244 L, and 1.37 ng/mL, respectively. Using the median weight and postmenstrual age of our subjects (i.e., 1.2 kg and 28 wk) in the final model, the typical unbound hydrocortisone clearance and volume of distribution were 1.0 L/hr and 4.2 L, respectively. The typical half-life for unbound hydrocortisone was 2.9 hours. A sharp and continuous increase in unbound hydrocortisone clearance was observed at 35 weeks postmenstrual age.

CONCLUSIONS

We report the first pharmacokinetic data for unbound hydrocortisone, the pharmacologically active moiety, in critically ill neonates and infants with vasopressor-resistant hypotension. Unbound hydrocortisone clearance increased with body weight and was faster in children with an older postmenstrual age. Unbound hydrocortisone clearance increased sharply at 35 weeks postmenstrual age and continued to mature thereafter. This study lays the groundwork for evaluating unbound hydrocortisone exposure-response relationships and drawing definitive conclusions about the dosing of IV hydrocortisone in critically ill neonates and infants with vasopressor-resistant hypotension.

Dispatches from the interface of salivary bioscience and neonatal research

The emergence of the interdisciplinary field of salivary bioscience has created opportunity for neonatal researchers to measure multiple components of biological systems non-invasively in oral fluids. The implications are profound and potentially high impact. From a single oral fluid specimen, information can be obtained about a vast array of biological systems (e.g., endocrine, immune, autonomic nervous system) and the genetic polymorphisms related to individual differences in their function. The purpose of this review is to describe the state of the art for investigators interested in integrating these unique measurement tools into the current and next generation of research on gonadal steroid exposure during the prenatal and neonatal developmental periods.

Approaches to salivary cortisol collection and analysis in infants

Salivary cortisol is becoming more commonly utilized as a biologic marker of stress in observational studies and intervention research. However, its use with infants (12 months of age or younger) is less widespread and poses some special challenges to researchers. In order to decide on the most suitable collection procedure for salivary cortisol in infants, a number of criteria should be considered. This article will aid investigators interested in integrating salivary cortisol measurement into their research studies by presenting (1) an overview of the patterns of cortisol secretion in infancy including the development of diurnal rhythm and response to stress; (2) a comparison of the most commonly used approaches for collecting salivary cortisol samples in infants including cotton rope, syringe aspiration technique, filter paper, hydrocellulose microsponge, and the Salimetrics children's swab; (3) a discussion of the factors contributing to heightened cortisol variability in infancy and how these can be limited; (4) analytical issues associated with cortisol measurement; and (5) examples of criteria to consider when choosing a saliva sampling method and lab for conducting assays.