The pituitary-adrenal responses to exogenous human corticotropin-releasing hormone in preterm, very low birth weight infants

Unmitigated Surgical Castration in Calves of Different Ages: Cortisol Concentrations, Heart Rate Variability, and Infrared Thermography Findings

Simple Summary

In the United States, castration is a common husbandry procedure utilized in the cattle industry. Despite castration being painful, it is commonly performed without the use of analgesia, one reason being the lack of available approved analgesics in the United States for use in alleviating pain associated with castration in cattle. Additionally, if pain mitigation is used, it is more often provided to older animals as there is a notion that younger animals experience pain to a lesser degree than older ones. The aim of this study was to characterize physiological responses to unmitigated surgical castration in calves of varying ages in terms of cortisol concentration, heart rate variability, and changes in eye temperature. Overall, our results indicate that the measured physiological responses to castration differed between age groups and changed over time post-castration. Younger calves showed a different response pattern than older calves for many of the variables measured suggesting that the response to castration-induced pain may be age-specific. For example, the youngest calves had lower cortisol and average eye temperature as compared to the oldest calves. Additionally, many variables showed a differential response to castration-induced pain, as compared with simulated castration, thus suggesting physiological indicators that could be targeted in future development and validation of analgesics for alleviation of pain associated with castration in cattle.

Abstract

The objective was to characterize physiological responses to unmitigated surgical castration in calves of varying ages. Thirty male Holstein calves of three ages [<6 w (6W); 3 m (3M); 6 m (6M); n = 10] underwent a simulated castration treatment (SHAM) followed 24 h later by castration (CAST). For both treatments, heart rate variability, eye temperature, and cortisol were measured over time from treatment to specified end points to capture the acute response period. Interactions between treatment and age (p = 0.035) and time and age (p < 0.001) were noted for cortisol. The 6W calves had lower cortisol compared to 6M calves at SHAM and CAST. Cortisol of 6W calves decreased from peak to pre-treatment levels faster than 6M calves. An interaction between time and age was reported in squared differences of inter-beat-intervals (RMSSD; p = 0.02) and high-frequency power (HFP; p = 0.05), whereby both responses decreased in 6W calves during the sampling period which was not seen in 3M and 6M calves. Average eye temperature (AET) differed by age (p = 0.0018) whereby 6W calves had lower AET than 6M calves (p = 0.0013) regardless of treatment and time. The findings suggest that responses to unmitigated surgical castration seem to be mediated by the autonomic nervous system in an age-related manner.

Antenatal Glucocorticoids Reduce the Incidence of Refractory Hypotension in Low Birthweight Infants during the Early Neonatal Period, but Do Not Affect It beyond This Time

OBJECTIVE

This study aimed to clarify the effect of antenatal glucocorticoids (AGs) on the incidence of refractory hypotension (RH) in very low birthweight (VLBW) infants after the first week of life.

STUDY DESIGN

We included VLBW infants born at a gestational age of <30 weeks and divided them into three groups: the complete group (born within 7 days of completing a single course [two doses] of AGs), the incomplete group (born without complete course), and the late delivery group (born at ≥8 days after a single course). We compared the incidence and period of onset of RH among the three groups.

RESULTS

A total of 115 infants were enrolled. The incidence of RH in the first week of life was significantly lower in the complete group than in the other groups. However, there was no significant difference in the incidence of RH after the first week of life among the groups.

CONCLUSION

AGs contribute to circulatory stabilization during the first week of life, but this effect does not last after 1 or 2 weeks of administration. In infants who receive AGs, physicians should consider that the risk of RH after the first week of life is not low.

Plasma cortisol and ACTH levels in 416 VLBW preterm infants during the first month of life: distribution in the AGA/SGA population

OBJECTIVE

The aim of this study is to establish the serum level distribution of cortisol and ACTH in VLBW preterm newborns and determine which neonates are ideal candidates for the stimulation test for adrenal insufficiency.

METHODS

Plasma cortisol and ACTH levels were evaluated in 416 VLBW newborns on days 1, 7, and 30 of life. Gender, gestational age, weight, type of delivery, RDS prophylaxis, and perinatal morbidities were considered as potential variability factors.

RESULTS

Cortisol and ACTH levels significantly decreased between 1, 7, and 30 days. Significantly higher cortisol levels were found at lower gestational ages and in infants born by vaginal delivery, whereas lower levels were observed in those born after maternal corticosteroid treatment. The distribution of cortisol and ACTH levels in healthy infants born by cesarian section is presented.

CONCLUSION

Even if high or low levels were not frequently linked to illness, the presented distribution data may indicate that the newborns are ideal candidates for the stimulation test.

Glucocorticoid Programming in Very Preterm Birth

Very preterm (i.e., <32 weeks of gestation) infants admitted to the neonatal intensive care unit are compromised in their abilities to respond adequately to common threats like hemodynamic changes and reduced energy supplies, which is partly attributable to adrenocortical insufficiency. Conversely, later in life, these infants show features of increased glucocorticoid bioactivity, such as abdominal fat distribution, raised blood pressure, insulin resistance and diabetes mellitus type 2. It has been suggested that the very preterm newborn responds to the adverse postnatal environment with a sustained elevation in hypothalamus-pituitary-adrenal axis activity that persists beyond infancy. This has implications for subsequent growth, body composition, metabolism, neurodevelopment and, ultimately, long-term disease risk. The mechanisms underpinning these associations are not fully elucidated yet. This review gives a brief summary of studies that investigated adrenocortical function in very preterm newborns and how the axis changes with age, as a possible explanation for the association between prematurity and long-term outcome.

Late-onset circulatory collapse of prematurity

Late-onset circulatory collapse (LCC) is a refractory hypotension occurring after the early neonatal period (>day 7), in very low-birthweight infants. Typically, infants stabilized within the early neonatal period develop sudden onset of circulatory collapse after the early neonatal period. The underlying pathophysiology of LCC is considered to be relative adrenal insufficiency, which is well known in Japan, but is not widely accepted in North America or Europe. The current increase in LCC in Japan suggests that the principal trigger is related to recent trends in neonatal medicine and/or newly introduced treatments for preterm infants, but the pathophysiology has not been fully elucidated. In this review, based on current knowledge regarding LCC, the pathophysiology is discussed.

Neonatal hydrocortisone therapy does not have a serious suppressive effect on the later function of the hypothalamus-pituitary-adrenal axis

AIM

This study investigated whether providing extremely low birthweight (ELBW) infants with a large amount of hydrocortisone had a serious suppressive effect on the later function of the hypothalamus-pituitary-adrenal (HPA) axis.

METHODS

We evaluated the function of the HPA axis in 58 ELBW infants receiving 9.0 ± 7.2 mg/kg of intravenous and 68.1 ± 34.1 mg/kg of oral hydrocortisone using a human corticotropin-releasing hormone stimulation test. The mean age at investigation was 12.0 ± 5.2 months. The response was judged to be normal when the maximum to minimum ratio of the plasma adrenocorticotropic hormone (ACTH) concentration was >2, the peak value of the serum cortisol concentration was >552 nmol/L, or the increment was >193 nmol/L than baseline concentration.

RESULTS

Of the 58 infants studied, 51 (88%) displayed a normal response to both the ACTH and cortisol secretion and seven infants (12%) who were judged to be poor responders exhibited a peak cortisol value of >386 nmol/L without any episode of adrenal insufficiency.

CONCLUSION

Providing ELBW infants with a daily low dose of long-term hydrocortisone therapy should not lead to a serious suppressive effect on the later function of the HPA axis, regardless of the administration method.

Adrenal and thyroid function in the fetus and preterm infant

Adrenal and thyroid hormones are essential for the regulation of intrauterine homeostasis, and for the timely differentiation and maturation of fetal organs. These hormones play complex roles during fetal life, and are believed to underlie the cellular communication that coordinates maternal-fetal interactions. They serve to modulate the functional adaptation for extrauterine life during the perinatal period. The pathophysiology of systemic vasopressor-resistant hypotension is associated with low levels of circulating cortisol, a result of immaturity of hypothalamic-pituitary-adrenal axis in preterm infants under stress. Over the past few decades, studies in preterm infants have shown abnormal clinical findings that suggest adrenal or thyroid dysfunction, yet the criteria used to diagnose adrenal insufficiency in preterm infants continue to be arbitrary. In addition, although hypothyroidism is frequently observed in extremely low gestational age infants, the benefits of thyroid hormone replacement therapy remain controversial. Screening methods for congenital hypothyroidism or congenital adrenal hyperplasia in the preterm neonate are inconclusive. Thus, further understanding of fetal and perinatal adrenal and thyroid function will provide an insight into the management of adrenal and thyroid function in the preterm infant.

Diagnostic value of salivary cortisol in the CRH stimulation test in premature infants

CONTEXT

According to a recent nationwide survey in Japan, a significant proportion of very low birth weight infants (VLBWI) develop late-onset circulatory collapse after the first week of life. Small doses of glucocorticoid are very effective in these patients, and relative adrenal insufficiency is suspected to be the main cause of the condition. Although the CRH test is required to evaluate the hypothalamic-pituitary-adrenal axis, obtaining multiple blood samples is invasive.

OBJECTIVES

The present study was carried out to validate the consistency of the cortisol profiles of matched serum and saliva samples collected as part of the CRH test from VLBWI.

SUBJECTS/METHODS

In 23 VLBWI with a gestational age of less than 29 wk, we performed CRH tests at 2 wk after birth and at term. Their cortisol values were measured at the baseline and 30 min after the administration of a single dose of human CRH (1 μg/kg) using matched serum and saliva samples.

RESULTS

In 26 CRH tests in 19 infants, we were able to measure both serum and salivary cortisol. Significant correlations were detected between the infants' serum and salivary cortisol values (r=0.78; P<0.0001), the increases in these values induced in response to the CRH test (r=0.81; P<0.0001), and their peak serum and salivary cortisol values (r=0.68; P=0.0001).

CONCLUSION

This study indicated that using salivary cortisol measurements for the CRH test could be a reliable method for evaluating the hypothalamic-pituitary-adrenal axis in VLBWI with gestational age of less than 29 wk.

Effects of intrauterine exposure to synthetic glucocorticoids on fetal, newborn, and infant hypothalamic-pituitary-adrenal axis function in humans: a systematic review

BACKGROUND

Synthetic glucocorticoids are commonly used in reproductive medicine. Fetal organ systems are highly sensitive to changes in the intrauterine environment, including overexposure to glucocorticoids. Structural and functional alterations resulting from such changes may persist throughout life and have been associated with diverse diseases. One system that could be particularly sensitive to fetal glucocorticoid overexposure is the hypothalamic-pituitary-adrenal (hpa) axis. Many human studies have investigated this possibility, but a systematic review to identify consistent, emergent findings is lacking.

METHODS

We systematically review 49 human studies, assessing the effects of intrauterine exposure to synthetic glucocorticoids on fetal, neonate, and infant hpa function.

RESULTS

Study quality varied considerably, but the main findings held true after restricting the analyses to higher-quality studies: intrauterine exposure to synthetic glucocorticoids reduces offspring hpa activity under unstimulated conditions after pain but not pharmacological challenge. Although reduced unstimulated hpa function appears to recover within the first 2 wk postpartum, blunted hpa reactivity to pain is likely to persist throughout the first 4 months of life. There is some evidence that the magnitude of the effects is correlated with the total amount of glucocorticoids administered and varies with the time interval between glucocorticoid exposure and hpa assessment.

CONCLUSIONS

This systematic review has allowed the demonstration of the way in which intrauterine exposure to various regimens of synthetic glucocorticoids affects various forms of hpa function. As such, it guides future studies in terms of which variables need to be focused on in order to further strengthen the understanding of such therapy, whilst continuing to profit from its clinical benefits.

Relative adrenal insufficiency in the preterm and term infant

Cortisol release in the face of illness or stress is vital for survival. Relative adrenal insufficiency occurs when a patient's cortisol response is inadequate for the degree of illness or stress. Numerous studies have documented the existence of relative adrenal insufficiency in critically ill adults, and its association with increased morbidity and mortality. There is increasing evidence that relative adrenal insufficiency may be an etiology for hemodynamic instability and hypotension in the critically ill newborn, but compared with the adult population, there is still a paucity of data in this population. Randomized controlled trials are needed to evaluate the efficacy and safety of glucocorticoids for the treatment of cardiovascular insufficiency due to relative adrenal insufficiency in ill preterm and term newborn infants.

Cortisol production rates in preterm infants in relation to growth and illness: a noninvasive prospective study using gas chromatography-mass spectrometry

CONTEXT

Whereas intrauterine growth and maturation depend on low cortisol levels, an adrenal stress response postnatally is thought to be mandatory in preterm infants.

OBJECTIVE

The goal of this study was to determine cortisol production rates (CPRs) in preterm infants during early life with extreme illness and, thereafter, during extrauterine growth and maturation.

DESIGN

We describe a longitudinal observational study.

SETTING

The study was conducted at a university neonatal intensive care unit.

PATIENTS AND METHODS

Seventeen well (27.9 +/- 1.8 wk) and 44 ill (27.3 +/- 1.6 wk) preterm infants were classified by the Score for Neonatal Acute Physiology. Glucocorticoid metabolites were profiled by gas chromatography-mass spectrometry in 24-h urinary samples. Urine was collected noninvasively using cellulose nappies and extracted by hydraulic press.

RESULTS

Medians of CPRs (microg kg(-1) d(-1) mg creatinine) in ill (well) preterm infants were as follows: at d 1, 35 (40); d 2, 35 (40); d 3, 48 (53); d 5, 47 (41); wk 2, 72 (48); wk 3, 73 (37); wk 4, 54 (26). Regression analysis revealed a significant inverse influence of gestational age (P < 0.005) on the maximum of CPRs but not of severity of illness (Score for Neonatal Acute Physiology; P = 0.72). A mature adrenal response was found in only 12 of 44 (27%) ill preterm infants, who had CPRs higher than the 3-fold median of CPRs of well infants. This mature adrenal response was associated with a significantly higher incidence of cerebral bleeding: 9 of 12 (75%) vs. 8 of 32 (25%) without such a response (P = 0.003). During growth, CPRs of ill (well) preterm infants decreased: at month 2, 30 (18); month 3, 18 (22); correlation between weight gain and decrease of CPRs in ill infants between wk 4 and month 3, r = -0.48 (P = 0.027).

CONCLUSIONS

Severity of illness did not have a significant influence on CPRs in preterm infants. However, the highest CPRs were associated with a significantly higher incidence of cerebral bleeding. During growth, CPRs decreased significantly, suggesting that preterm infants have the ability to regulate cortisol production. CPRs in ill preterm infants might reflect inadequate stress reaction, but this could also reveal persistence of fetal protective mechanisms against high catabolic cortisol concentrations.

Transient adrenocortical insufficiency of prematurity and systemic hypotension in very low birthweight infants

OBJECTIVES

A proportion of preterm, very low birthweight (VLBW, < 1500 g) infants may show inadequate adrenal response to stress in the immediate postnatal period. The human corticotrophin releasing hormone (hCRH) stimulation test was used to: (a) determine the relation between pituitary-adrenal response and systemic blood pressure in these infants; (b) characterise the endocrinological features of transient adrenocortical insufficiency of prematurity (TAP).

STUDY DESIGN

A total of 226 hCRH tests were performed on 137 VLBW infants on day 7 and 14 of life in a tertiary neonatal centre.

RESULTS

Basal, peak, and incremental rise in serum cortisol (Delta Cort(0-30)) on day 7 were associated significantly with the lowest systolic, mean, and diastolic blood pressures recorded during the first two weeks of life (r > 0.25, p < 0.005). These cortisol concentrations also correlated significantly but negatively with the maximum and total cumulative dose of dopamine (r > -0.22, p < 0.02), dobutamine (r > -0.18, p < 0.04), and adrenaline (r > -0.26, p < 0.004), total volume of crystalloid (r > -0.22, p < 0.02), and duration of inotrope treatment (r > -0.25, p < 0.006). Multivariate regression analysis of significant factors showed that the lowest systolic, mean, and diastolic blood pressures remained independently associated with serum cortisol (basal, peak, and Delta Cort(0-30)) on day 7. Hypotensive infants requiring inotropes (group 2) were significantly less mature and more sick than infants with normal blood pressure (group 1). The areas under the ACTH response curves were significantly greater in group 2 than in group 1, on both day 7 (p = 0.004) and day 14 (p = 0.004). In contrast, the area under the cortisol response curve was significantly greater in group 1 than in group 2 on day 7 (p = 0.001), but there was no significant difference between the two groups on day 14. In addition, serum cortisol at the 50th centile in hypotensive infants had high specificity and positive predictive value (0.80-0.93 and 0.81-0.89 respectively) for predicting early neonatal hypotension.

CONCLUSIONS

This study characterises the fundamental endocrinological features of TAP: normal or exaggerated pituitary response; adrenocortical insufficiency; good recovery of adrenal function by day 14 of postnatal life. The results also provide the centiles of serum cortisol for hypotensive patients and infants with normal blood pressure, and show a significant relation between serum cortisol and blood pressure in VLBW infants.

Early pituitary-adrenal response and respiratory outcomes in preterm infants

OBJECTIVE

To assess the influence of circulating (basal) and stimulated plasma adrenocorticotrophin (ACTH) and serum cortisol on the duration of oxygen supplementation and development of chronic lung disease (CLD) in preterm, very low birthweight infants.

METHODS

A total of 226 human corticotrophin releasing hormone stimulation tests were performed on 137 very low birthweight infants on days 7 and 14 in a tertiary neonatal centre.

RESULTS

Multivariate regression analysis showed that the duration of oxygen supplementation was negatively associated with birth weight, but positively associated with alveolar-arterial oxygen gradient (A-aDO(2)) on the first day and with basal serum cortisol on day 14. In addition, the multivariate classification and regression trees model indicated that the two most useful indices for predicting CLD were clinical risk index for babies (CRIB) score (> 9) and peak serum cortisol (> 740 nmol/l) on day 14. The sensitivity, specificity, positive and negative predictive values of these factors for predicting CLD were 53%, 80%, 81%, and 70% respectively.

CONCLUSIONS

The findings suggest that birth weight, severity of initial respiratory failure as reflected by the A-aDO(2) gradient, and continuing "stress" with persistent increase in serum cortisol on day 14 are significant risk factors associated with the duration of oxygen supplementation, whereas early pituitary-adrenal response (basal and peak plasma ACTH and serum cortisol on day 7) is not an independent risk factor. Although CRIB score in combination with peak serum cortisol on day 14 are useful predictors of CLD, the need to use a stimulation test and the relatively late timing of the forecast render these indices unattractive for routine clinical use.

Maternal and fetal hypothalamic-pituitary-adrenal axes during pregnancy and postpartum

The principal modulators of the hypothalamic-pituitary-adrenal (HPA) axis are corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Corticotropin-releasing hormone is not exclusively produced in the hypothalamus. Its presence has been demonstrated at peripheral inflammatory sites. Ovulation and luteolysis bear characteristics of an aseptic inflammation. CRH was found in the theca and stromal cells as well as in cells of the corpora lutea of human and rat ovaries. The cytoplasm of the glandular epithelial cells of the endometrium has been shown to contain CRH and the myometrium contains specific CRH receptors. It has been suggested that CRH of fetal and maternal origin regulates FasL production, thus affecting the invasion (implantation) process through a local auto-paracrine regulatory loop involving the cytotrophoblast cells. Thus, the latter may regulate their own apoptosis. During pregnancy, the plasma level of circulating maternal immunoreactive CRH increases exponentially from the first trimester of gestation due to the CRH production in the placenta, decidua, and fetal membranes. The presence in plasma and amniotic fluid of a CRH-binding protein (CRHbp) that reduces the bioactivity of circulating CRH by binding is unique to humans. Maternal pituitary ACTH secretion and plasma ACTH levels rise during pregnancy-though remaining within normal limits-paralleling the rise of plasma cortisol levels. The maternal adrenal glands during pregnancy gradually become hypertrophic. Pregnancy is a transient, but physiologic, period of hypercortisolism. The diurnal variation of plasma cortisol levels is maintained in pregnancy, probably due to the secretion of AVP from the parvicellular paraventricular nuclei. CRH is detected in the fetal hypothalamus as early as the 12th week of gestation. CRH levels in fetal plasma are 50% less than in maternal plasma. The circulating fetal CRH is almost exclusively of placental origin. The placenta secretes CRH at a slower rate in the fetal compartment. AVP is detected in some neurons of the fetal hypothalamus together with CRH. AVP is usually detectable in the human fetal neurohypophysis at 11 to 12 weeks gestation and increases over 1000-fold over the next 12 to 16 weeks. The role of fetal AVP is unclear. Labor appears to be a stimulus for AVP release by the fetus. The processing of POMC differs in the anterior and intermediate lobes of the fetal pituitary gland. Corticotropin (ACTH) is detectable by radioimmunoassay in fetal plasma at 12 weeks gestation. Concentrations are higher before 34 weeks gestation, with a significant fall in late gestation. The human fetal adrenal is enormous relative to that of the adult organ. Adrenal steroid synthesis is increased in the fetus. The major steroid produced by the fetal adrenal zone is sulfoconjugated dehydroepiandrosterone (DHEAS). The majority of cortisol present in the fetal circulation appears to be of maternal origin, at least in the nonhuman primate. The fetal adrenal uses the large amounts of progesterone supplied by the placenta to make cortisol. Another source of cortisol for the fetus is the amniotic fluid where cortisol converted from cortisone by the choriodecidua, is found. In humans, maternal plasma CRH, ACTH, and cortisol levels increase during normal labor and drop at about four days postpartum; however, maternal ACTH and cortisol levels at this stage are not correlated. In sheep, placental CRH stimulates the fetal production of ACTH, which in turn leads to a surge of fetal cortisol secretion that precipitates parturition. The 10-day-long intravenous administration of antalarmin, a CRH receptor antagonist, significantly prolonged gestation compared to the control group of animals. Thus, CRH receptor antagonism in the fetus can also delay parturition. The HPA axis during the postpartum period gradually recovers from its activated state during pregnancy. The adrenals are mildly suppressed in a way analogous to postcure Cushing's syndrome. Provocation testing has shown that hypothalamic CRH secretion is transiently suppriently suppressed at three and six weeks postpartum, normalizing at 12 weeks.

The corticotrophin-releasing hormone test in preterm infants

OBJECTIVE

The developing hypothalamic--pituitary--adrenal axis (HPAA) may be immature and not yet fully functional in preterm infants. This may result in an inappropriate adrenal response to stress. Little is known about the pituitary--adrenal response to corticotrophin-releasing hormone (CRH) stimulation during the early neonatal period in preterm infants born before 32 weeks of gestation. Therefore, in a first study we investigated the pituitary--adrenal response to 1 microg/kg CRH i.v. in 13 preterm infants born less-than-or-equal 32 weeks of gestation. In addition, in a randomized placebo-controlled study we compared the pituitary--adrenal response of 1 microg/kg CRH to placebo and stimulation with 2 microg/kg CRH.

RESULTS

In the first study, the level of ACTH increased from 6.9 +/-2.1 to 11.6 +/- 5.1 pmol/l (P < 0.01) and cortisol increased from 350 plus minus 115 to 582 +/- 201 nmol/l (P < 0.05). Thirty-eight percent of the studied infants showed a maximal level of ACTH < 9 pmol/l, and 15% showed a maximal level of cortisol < 360 nmol/l. In the randomized study, infants in the 1 microg/kg and in the 2 microg/kg CRH group, but not in the placebo group, showed a significant increase in cortisol and ACTH after stimulation (P < 0.01). Stimulated levels of ACTH and cortisol were significantly higher in the 2 microg/kg group compared with the placebo and the 1 microg/kg group. No differences were found for plasma ACTH and cortisol levels in the 1 microg/kg group compared with the placebo group. Basal levels of cortisol and ACTH obtained from the first and from the randomized study correlated significantly (n = 29; r = 0.42, P < 0.03). In addition, in infants stimulated with 1 microg/kg CRH a lower cortisol response correlated with a longer stay in hospital (n = 13; r = --0.57, P < 0.05).

CONCLUSIONS

In this study we show that a 1 microg/kg CRH stimulation test in preterm infants results more often in an inappropriate adrenal response while stimulation with 2 microg/kg CRH gives rise to an appropriate response in all studied infants. Furthermore, stimulation with 2 microg/kg CRH results in higher levels of ACTH and cortisol compared to placebo and 1 microg/kg CRH. We conclude that in preterm infants the ability of the pituitary to respond adequately to CRH stimulation depends on the dose of CRH used and may also be dependent on the maturity of the pituitary--adrenal axis.

Refractory hypotension in preterm infants with adrenocortical insufficiency

Five preterm, very low birthweight infants with severe hypotension and adrenocortical insufficiency are described. The profound hypotension was resistant to volume expansion and inotrope treatment, but responded promptly to corticosteroid treatment. A human corticotrophin releasing hormone (hCRH) test performed before corticosteroid treatment showed adequate pituitary response, and the endocrine dysfunction was identified at the adrenal level. Corticosteroid treatment should be considered and could be life saving in severely hypotensive preterm infants who do not respond to conventional treatment with volume expanders and inotropes.

Adrenocorticotropin and corticotropin-releasing hormone tests in preterm infants

The short ACTH test is used in evaluating the hypothalamo-pituitary-adrenal axis (HPA-axis) in preterm neonates after dexamethasone treatment. This test mainly examines primary adrenal suppression but is also used as a method to test secondary adrenal insufficiency because long-term deprivation of ACTH causes atrophy of the adrenal cortex. The CRH test, on the other hand, directly examines the function of the pituitary. We tested 18 infants in the neonatal intensive care unit with both the ACTH test and the CRH test to determine which of these two tests more reliably demonstrates HPA-axis suppression. One patient had normal responses both in the ACTH test and in the CRH test when the limit of 360 nmol/L was used as a sign of proper cortisol secretion. In four cases the patients' cortisol secretion would have been regarded as normal by the low-dose ACTH test, whereas the CRH test did not show an adequate cortisol response. In conclusion, the ACTH test did not reliably indicate HPA-axis suppression after a short (<2 weeks) course of dexamethasone therapy in this study. Therefore, whether the infant is or will be under acute stress after short glucocorticoid treatment, ensuring adequate cortisol secretion with the CRH test should be considered.

Leptin and metabolic hormones in infants of diabetic mothers

AIMS

To investigate the effect of maternal diabetes on leptin in term newborns and to determine whether leptin correlates with insulin and its associated biochemical parameters in support of the hypothesis that a functional "adipoinsular axis" might exist at this stage of development.

METHODS

A total of 116 term newborns were prospectively enrolled and categorised into three groups: 44 were infants of non-diabetic mothers (control group C); 41 were infants born to mothers with gestational diabetes on dietary treatment (group D); and 31 were infants born to mothers with gestational or pregestational diabetes on insulin treatment (group I).

RESULTS

No significant difference in serum leptin was observed between the three groups; the results of the study population were therefore pooled and analysed. Serum leptin correlated significantly with serum insulin, insulin:glucose ratio, birth weight, body length, body mass index, placenta weight, and maternal HbA(1c). Female infants had significantly higher serum leptin than male infants. All parameters except placenta weight and body length remained significantly associated with serum leptin when multivariate stepwise regression analysis was applied. Subgroup analysis revealed a significant correlation between serum leptin and cortisol in group D.

CONCLUSIONS

There was no significant difference in serum leptin between infants born to diabetic and non-diabetic mothers, though infants born to mothers requiring insulin treatment had the highest median serum leptin concentrations. The significant association between serum leptin and insulin or insulin:glucose ratio supports the hypothesis that a functional adipoinsular axis might exist in term newborns. Furthermore, the significant correlation between maternal HbA(1c) and circulating leptin of the studied infants suggests that the clinical control of maternal diabetes could affect the regulation of serum leptin in these infants.