Changes in prolactin secretion in the short- and long-term after adrenalectomy / Efeito da evolução temporal da adrenalectomia na secreção de prolactina

OBJECTIVE: To evaluate the modulation of the hypothalamus-pituitary-adrenal axis (HPA) on prolactin secretion in rats after adrenalectomy (ADX). MATERIALS AND METHODS: Plasma corticosterone, ACTH, and prolactin concentrations were measured by radioimmunoassay in rats after bilateral ADX in the short- (3 hours and 1day) and long-term (3, 7, and 14 days). RESULTS: Animals that underwent ADX showed undetectable corticosterone levels and a triphasic ACTH response with a transient increase (3h), a decrease (1d), and further increase in the long-term after ADX. Sham animals showed a marked increase in corticosterone and ACTH levels three hours after surgery, with a decrease to basal levels thereafter. Plasma prolactin levels were not changed after ADX. CONCLUSION: There are different points of equilibrium in the HPA axis after the glucocorticoid negative feedback is removed. Prolactin plasma secretion is not altered in the short or long- term after ADX, suggesting that the peptidergic neurons essential for prolactin release are not activated after ADX.

OBJETIVO: Avaliar a modulação do eixo hipotálamo-hipófise-adrenal (HHA) sobre a secreção de prolactina após adrenalectomia (ADX). MATERIAIS E MÉTODOS: Quantificamos por RIE corticosterona, ACTH e prolactina plasmáticos em ratos após curtos (3 horas e 1 dia) e longos (3, 7 e 14 dias) períodos de ADX bilateral. RESULTADOS: Animais ADX mostraram níveis indetectáveis de corticosterona. As concentrações plasmáticas de ACTH apresentaram resposta trifásica: aumento transitório (3h), diminuição (1d) e novo aumento após longos períodos de ADX. Animais Sham mostraram aumento de corticosterona/ACTH após três horas de cirurgia, diminuindo posteriormente aos níveis basais. As concentrações plasmáticas de prolactina não se alteraram após ADX. CONCLUSÃO: Existem diferentes pontos de equilíbrio do eixo HHA após a remoção da retroalimentação negativa exercida pelos glicocorticoides. A secreção de prolactina não se alterou após curtos/longos períodos de ADX, sugerindo que os neurônios peptidérgicos essenciais para a liberação de prolactina não estão ativados durante os diferentes períodos de ADX.

Avaliação do eixo hipotálamo-hipófise adrenal no diagnóstico e na remissão da doença de Cushing / Assessment of the hypothalamic-pituitary-adrenal axis in Cushing's disease diagnosis and remission

A doença de Cushing (DC) permanece um desafio médico com muitas questões ainda não respondidas. O sucesso terapêutico dos pacientes com DC está ligado à correta investigação do diagnóstico síndrômico e etiológico, além da experiência e talento do neurocirurgião. A adenomectomia hipofisária transesfenoidal constitui-se no tratamento de escolha para a DC. A avaliação da remissão da doença no pós-operatório e da recorrência em longo prazo constitui um desafio ainda maior. Especial destaque deve ser dado para o cortisol sérico no pós-operatório como marcador de remissão. Adicionalmente, o uso de corticoide exógeno no pós-operatório apenas em vigência de insuficiência adrenal tem sido sugerido por alguns autores como requisito essencial para permitir a correta interpretação do cortisol sérico nesse cenário. Neste artigo, revisamos as formas de avaliação da atividade da DC e os marcadores de remissão e recidiva da DC após a realização da cirurgia transesfenoidal.

Cushing's disease (CD) remains a medical challenge, with many questions still unanswered. Successful treatment of CD patients is closely related to correct approach to syndromic and etiological diagnosis, besides the experience and talent of the neurosurgeon. Pituitary transsphenoidal adenomectomy is the treatment of choice for DC. Assessment of remission after surgery and recurrence in the long term is an even greater challenge. In this regard, special attention should be paid to the role of postoperative serum cortisol as a marker of CD remission. Additionally, the postoperative use of exogenous glucocorticoids only in cases of adrenal insufficiency has been suggested by some authors as an essential practice to enable the use of serum cortisol in this scenario. In this article, we review the forms of evaluation of DC activity, and markers of remission and relapse of CD after transsphenoidal surgery.

Neural regulation of the stress response: glucocorticoid feedback mechanisms

The mammalian stress response is an integrated physiological and psychological reaction to real or perceived adversity. Glucocorticoids are an important component of this response, acting to redistribute energy resources to both optimize survival in the face of challenge and to restore homeostasis after the immediate challenge has subsided. Release of glucocorticoids is mediated by the hypothalamo-pituitary-adrenal (HPA) axis, driven by a neural signal originating in the paraventricular nucleus (PVN). Stress levels of glucocorticoids bind to glucocorticoid receptors in multiple body compartments, including the brain, and consequently have wide-reaching actions. For this reason, glucocorticoids serve a vital function in negative feedback inhibition of their own secretion. Negative feedback inhibition is mediated by a diverse collection of mechanisms, including fast, non-genomic feedback at the level of the PVN, stress-shut-off at the level of the limbic system, and attenuation of ascending excitatory input through destabilization of mRNAs encoding neuropeptide drivers of the HPA axis. In addition, there is evidence that glucocorticoids participate in stress activation via feed-forward mechanisms at the level of the amygdala. Feedback deficits are associated with numerous disease states, underscoring the necessity for adequate control of glucocorticoid homeostasis. Thus, rather than having a single, defined feedback ‘switch’, control of the stress response requires a wide-reaching feedback ‘network’ that coordinates HPA activity to suit the overall needs of multiple body systems.

Cortisol Awakening Response and Nighttime Salivary Cortisol Levels in Healthy Working Korean Subjects

PURPOSE: Cortisol awakening response (CAR) and nighttime cortisol levels have been used as indices of adrenocortical activity. However, population-based statistical information regarding these indices has not been provided in healthy subjects. This study was carried out to provide basic statistical information regarding these indices. MATERIALS AND METHODS: Cortisol levels were measured in saliva samples collected immediately upon awakening (0 min), 30 min after awakening and in the nighttime on two consecutive days in 133 healthy subjects. RESULTS: We determined the mean [standard deviation (SD)], median (interquartile range) and 5th-95th percentile range for each measure and auxiliary indices for CAR, i.e., the secreted cortisol concentration within 30 min of awakening (CARscc) and absolute and relative increases in cortisol level within 30 min of awakening (CARi and CARi%, respectively). We also determined these values for auxiliary indices derived from nighttime cortisol level, i.e., the ratio of cortisol level 30 min after awakening (CA30 min) to nighttime level (CA30 min/NC), as well as absolute and relative decreases in cortisol levels from CA30 min to nighttime (DCd and DCd%, respectively). We found no significant differences in cortisol level for any time point or in auxiliary indices between collection days, genders and ages. CONCLUSION: The provided descriptive information and statistics on the CAR and nighttime cortisol level will be helpful to medical specialists and researchers involved in hypothalamus-pituitary-adrenal axis assessment.

A pilot study on hypothalamo-pituitary-adrenocortical axis in primary hyperparathyroidism.

Background & objectives: Parathormone (PTH) and calcium, both have been shown to stimulate adrenal steroidogenesis in animal models and in vitro experiments. This is attributed to structural similarity between 15-25 amino acid region of the parathyroid hormone (PTH) and 1-11 amino acid region of adrenocorticotropin (ACTH). However, there are no in vivo human data regarding the effect of PTHcalcium axis on adrenocortical function. Materials: Ten patients with primary hyperparathyroidism underwent evaluation for cortisol dynamics including 0800 h and 2000 h plasma cortisol on day 1, cortisol response to insulin induced hypoglycaemia (IIH) on day 2, and 1 mg overnight dexamethasone suppression test (ONDST) on day 4. Serum aldosterone was also measured at 0800 h in fasting state on salt ad libitum for three days. These parameters were repeated 3 months after curative parathyroidectomy. Results: Basal plasma cortisol level at 0800 h and 2000 h were within upper normal range and loss of circadian rhythm in cortisol secretion was observed in half and forty per cent of patients had nonsuppressibility with ONDST. The defined peak cortisol response to insulin induced hypoglycaemia (>550 nmol/l) was achieved in all and nearly one third of patients had exaggerated response (>2000 nmol/l). After curative parathyroidectomy, the abnormalities in circadian rhythm and non-suppressibility with ONDST continued to prevail in 40 per cent of patients. The peak cortisol response to IIH showed a decrement but remained higher than normal. No correlation was observed between circulating parathyroid hormone and calcium with cortisol levels. Serum aldosterone was in upper normal range pre - and postoperatively, though it decreased postoperatively, but it could not attain a statistical significance (p = 0.5). Interpretation & conclusion: Abnormalities in hypothalamo-pituitary-adrenocortical axis in primary hyperparathyroidism do occur, however these are inconsistent and do not recover in majority of patients even after 3 months of curative parathyroidectomy.

Central actions of glucocorticoids in the control of body fluid homeostasis: review

The involvement of the hypothalamic-pituitary-adrenal axis in the control of body fluid homeostasis has been extensively investigated in the past few years. In the present study, we reviewed the recent results obtained using different approaches to investigate the effects of glucocorticoids on the mechanisms of oxytocin and vasopressin synthesis and secretion in response to acute and chronic plasma volume and osmolality changes. The data presented here suggest that glucocorticoids are not only involved in the mechanisms underlying the fast release but also in the transcriptional events that lead to decreased synthesis and secretion of these neuropeptides, particularly oxytocin, under diverse experimental conditions of altered fluid volume and tonicity. The endocannabinoid system, through its effects on glutamatergic neurotransmission within the hypothalamus and the nuclear factor κB-mediated transcriptional activity, seems to be also involved in the specific mechanisms by which glucocorticoids exert their central effects on neurohypophyseal hormone synthesis and secretion.

Repercussões imunológicas dos distúrbios do sono: o eixo hipotálamo-pituitária-adrenal como fator modulador / Immune outcomes of sleep disorders: the hypothalamic-pituitary-adrenal axis as a modulatory factor

OBJETIVO: Revisar a literatura a respeito da interação entre sono e sistema imunológico. MÉTODO: Busca no Web of Science e no PubMed com os descritores: sono, privação de sono, estresse, eixo hipotálamo-pituitária-adrenal, sistema imunológico e doenças auto-imunes. RESULTADOS: Foram encontrados 588 artigos no Web of Science. As 61 referências mais significativas e mais relacionadas aos objetivos do estudo foram utilizadas. Foram incluídos artigos originais e de revisão. CONCLUSÃO: A privação de sono e o sistema imunológico exercem e sofrem influências mútuas. A privação de sono é considerada um estressor, uma vez que induz a elevação do cortisol em seres humanos - ou da corticosterona em roedores. Os glicocorticóides, por sua vez, exercem um efeito imunossupressor. Por essas razões, foi proposto que o aumento da ativação do eixo hipotálamo-pituitária-adrenal seja um importante mediador das alterações imunológicas observadas em pacientes com insônia ou privados de sono.

OBJECTIVE: To review the literature on the interaction between sleep and the immune system. METHOD: A search on Web of Science and Pubmed database including the keywords sleep, sleep deprivation, stress, hypothalamic-pituitary-adrenal axis, immune system, and autoimmune diseases. RESULTS: On Web of Science, 588 publications were retrieved; 61 references, more significant and closer to our objective, were used, including original articles and review papers. CONCLUSION: Sleep deprivation and immune system exert a bidirectional influence on each other. Since sleep deprivation is considered a stressor, inasmuch as it induces elevation of cortisol or corticosterone levels in humans and rodents, respectively, and given the well-known immunosuppressive effect of glucocorticoids, we propose that increased activation of the hypothalamic-pituitary-adrenal axis is a major mediator of the immune alterations observed in patients with insomnia or in sleep deprived subjects.

Salivary cortisol to assess the hypothalamic-pituitary-adrenal axisin healthy children under 3 years old

OBJETIVO: Estabelecer intervalos de concentrações referenciais de cortisol salivar em crianças saudáveis, nos períodos matutino e vespertino, verificando os fatores de interferência nessa dosagem e a possibilidade de presença de ritmo circadiano. MÉTODOS: Pesquisa observacional controlada, incluindo aleatoriamente 91 crianças com idade de 45 dias a 36 meses, residentes em comunidade de Santo André (SP). Critérios de inclusão: nutridas, saudáveis, sem febre ou uso de corticóide, subdivididas em faixas etárias (cinco subgrupos) com intervalo de 6 meses. Houve coleta de saliva domiciliar nos períodos manhã e tarde para dosagem de cortisol, sob radioimunoensaio com anticortisol 3-oxima-albumina bovina. RESULTADOS: Os cinco subgrupos apresentaram dosagens matutinas superiores às vespertinas (p < 0,001), com diferença superior a 30 por cento a partir de 1 ano de idade. Valor médio em nmol/L foi de 557,86 (manhã) e 346,36 (tarde). Observou-se correlação linear negativa na dosagem matutina para horas de repouso e freqüência de dieta (p < 0,05); na vespertina, para medidas antropométricas (p < 0,05). CONCLUSÕES Foram estabelecidos valores de referência de normalidade de cortisol salivar em crianças saudáveis, e aos 45 dias foi possível observar ritmo circadiano, que atingiu maturidade aos 12 meses de vida. Privações de sono e dieta elevaram valores de cortisol matutino.

OBJECTIVE: To establish reference concentration intervals for salivary cortisol in healthy children, in the morning and in the afternoon, investigating factors that interfere with the concentration measured and the possibility that circadian rhythms are present. METHODS: A controlled observational study was carried out with 91 children aged 45 days to 36 months, selected at random and living in Santo André, state of São Paulo, Brazil. Inclusion criteria were: healthy, well-nourished, free from fever and corticoid use, subdivided by age group (five subsets) at 6-month intervals. Saliva was collected during home visits in the morning and afternoon. Cortisol was radioimmunoassayed with cortisol 3-oxime-bovine albumin antiserum. RESULTS: The five subsets exhibited higher cortisol concentration during the morning than in the afternoon (p < 0.001), and this difference passed 30 percent from 1 year of age onwards. Mean concentrations, in nmol/L, were 557.86 (morning) and 346.36 (afternoon). A negative linear correlation was observed between morning concentrations and hours' sleep and frequency of meals (p < 0.05), and in the afternoon with anthropometric measurements (p < 0.05). CONCLUSIONS: Reference values for normal salivary cortisol in healthy children were established. At 45 days it was possible to observe circadian rhythms, which reached maturity at 12 months of life. Sleep and food deprivation increased morning cortisol levels.

Plasma cortisol response to 1-24 adrenocorticotropin in patients with treated/untreated sellar & suprasellar mass lesions.

BACKGROUND & OBJECTIVES: One microgram short synacthene test is widely recommended as a screening test for evaluation of hypothalamo-pituitary-adrenocortical axis in patients with secondary adrenal insufficiency. Information on adequacy of cortisol response to this dose at different periods of the day in patients with hypothalamic-pituitary disorders is not available. Hence, this study was designed to assess the adequacy of cortisol response to 1 microg 1-24 adrenocorticotropin (ACTH) at 0800 h and 1600 h in patients with sellar and suprasellar mass lesions. METHODS: Thirty five consecutive patients with sellar and suprasellar mass lesions with mean age of 43.0+/-14.4 yr and 36 healthy controls with mean age of 32.3+/-9.0 yr were studied after obtaining informed consent. Maintenance doses of glucocorticoids in these patients were discontinued appropriately. On day 1, prestimulated and stimulated plasma cortisol samples at 0800 h and at 30 and 60 min following i.v. bolus of 1 microg 1-24 ACTH were collected. While on day 3, plasma cortisol samples were similarly collected at 1600 h. Cortisol estimation was done by a sensitive and specific radioimmunoassay. Stimulated plasma cortisol of 500 nmol/l or higher was defined as a normal response. RESULTS: In healthy controls, the prestimulated and peak cortisol levels at 0800 h (377.5+/-93.3 and 729.1+/-183.2 nmol/l) were higher (P<0.001 and P<0.01) than those at 1600 h (230.1+/-75.7 and 665.8+/-138.6 nmol/l). All subjects had a cortisol response of 500 nmol/l or higher in response to 1 microg 1-24 ACTH both at 0800 and 1600 h. In the patients' group, the prestimulated plasma cortisol at 0800 h (250.3+/-169.7 nmol/l) was higher (P<0.001) than that at 1600 h (166.3+/-128.9 nmol/l), while the peak cortisol response was comparable (P>0.05) in the morning as well as in the evening (490.9+/-309.4 vs 464.8+/-318.4). In 27 patients (77%) the morning and evening stimulated cortisol response to 1 microg 1-24 ACTH was consistent (normal in 13 and subnormal in 14) but was discrepant in the remaining 8 (23%). In 7 of these 8 patients, cortisol response was normal at 0800 h but not at 1600 h, while in only one, normal response was seen at 1600 h but not at 0800 h. INTERPRETATION & CONCLUSION: The demonstration of normal peak cortisol response to 1 microg 1-24 ACTH at 0800 h but not at 1600 h in substantial number of patients with sellar and suprasellar mass lesions suggests preference to morning for performing this test.

Stress and hippocampus / 法医学杂志

This review summarizes the present advance of effects of stress on hippocampal structure and function and the role of hippocampus in feedback regulation of thalamic-pituitary-adrenocortical (HPA) axis during stress. It shows that stress can affect hippocampal structure and function, on the other hand, the hippocampus can also suppress the stress reaction through the feedback regulation of HPA axis, but chronic stress can attenuate this regulation, then significantly impair its structure and function.

Role of the hypothalamic pituitary adrenal axis in the control of the response to stress and infection

The release of adrenocorticotropin (ACTH) from the corticotrophs is controlled principally by vasopressin and corticotropin-releasing hormone (CRH). Oxytocin may augment the release of ACTH under certain conditions, whereas atrial natriuretic peptide acts as a corticotropin release-inhibiting factor to inhibit ACTH release by direct action on the pituitary. Glucocorticoids act on their receptors within the hypothalamus and anterior pituitary gland to suppress the release of vasopressin and CRH and the release of ACTH in response to these neuropeptides. CRH neurons in the paraventricular nucleus also project to the cerebral cortex and subcortical regions and to the locus ceruleus (LC) in the brain stem. Cortical influences via the limbic system and possibly the LC augment CRH release during emotional stress, whereas peripheral input by pain and other sensory impulses to the LC causes stimulation of the noradrenergic neurons located there that project their axons to the CRH neurons stimulating them by alpha-adrenergic receptors. A muscarinic cholinergic receptor is interposed between the alpha-receptors and nitric oxidergic interneurons which release nitric oxide that activates CRH release by activation of cyclic guanosine monophosphate, cyclooxygenase, lipoxygenase and epoxygenase. Vasopressin release during stress may be similarly mediated. Vasopressin augments the release of CRH from the hypothalamus and also augments the action of CRH on the pituitary. CRH exerts a positive ultrashort loop feedback to stimulate its own release during stress, possibly by stimulating the LC noradrenergic neurons whose axons project to the paraventricular nucleus to augment the release of CRH.

The neuroimmune-endocrine axis: pathophysiological implications for the central nervous system cytokines and hypothalamus-pituitary-adrenal hormone dynamics

Cytokines are molecules that were initially discovered in the immune system as mediators of communication between various types of immune cells. However, it soon became evident that cytokines exert profound effects on key functions of the central nervous system, such as food intake, fever, neuroendocrine regulation, long-term potentiation, and behavior. In the 80's and 90's our group and others discovered that the genes encoding various cytokines and their receptors are expressed in vascular, glial, and neuronal structures of the adult brain. Most cytokines act through cell surface receptors that have one transmembrane domain and which transduce a signal through the JAK/STAT pathway. Of particular physiological and pathophysiological relevance is the fact that cytokines are potent regulators of hypothalamic neuropeptidergic systems that maintain neuroendocrine homeostasis and which regulate the body's response to stress. The mechanisms by which cytokine signaling affects the function of stress-related neuroendocrine systems are reviewed in this article.

Hypothalamo-pituitary response before and after surgical stress [splenectomy] in Thalassemic patients

Multiple endocrinopathy is a common manifestation in thalassemia. Although the response of the stress hormones to induced hypoglycemia has been studied in these patients, the impact of surgical stress is not yet determined. The hypothalamo-pituitary-adrenal axis of 27 thalassemic patients [TP], [4-15 years old [y.]] admitted for splenectomy, was evaluated before and after surgical stress during 1996-8. Blood samples for measurement of ACTH, cortisol, growth hormone [GH], thyroid stimulating hormone [TSH] and prolactin [PRL] were taken a day before and also approximately two hours after surgical insult. For comparison, 22 non-thalassemic patients [NTP] [3.5-14 y.] admitted for elective laparotomy, were selected as the control group. The cortisol response after surgical stress was significantly higher than baseline in both the TP [17.4 +/- 6.3 vs 30.81 +/- 11.49 micro g/dl; P<0.001] and the NTP [20.65 +/- 9.1 vs 36.87 +/- 11.08 micro g/dl; P<0.001]. NTP showed a significant elevation of ACTH upon surgical stress [P<0.001], while the difference between pre- and post-stress ACTH was not statistically significant in TP [P=0.123]. However, the ACTH concentration before operation in TP. was significantly higher than that of NTP [P<0.042] with no remarkable difference after surgical stress between the two groups [P=0.261]. GH increased significantly after operation in TP and NTP [P< 0.016 and <0.05, respectively]. A significant change in TSH [P< 0.03] and PRL [P< 0.004] was also observed in TP after operation. The hypothalamo-pituitary as well as the pituitary-adrenal axes are usually intact and responsive in TP. It is concluded that, the remarkable increase in ACTH concentration before operation may be due to a decreased adrenal reserve. Thus, the possibility of primary partial adrenal insufficiency, particularly under stress situations, should be considered in every thalassemic patient

Neonatal handling induces anovulatory estrous cycles in rats

Since previous work has shown that stimulation early in life decreases sexual receptiveness as measured by the female lordosis quotient, we suggested that neonatal handling could affect the function of the hypothalamus-pituitary-gonadal axis. The effects of neonatal handling on the estrous cycle and ovulation were analyzed in adult rats. Two groups of animals were studied: intact (no manipulation, N = 10) and handled (N = 11). Pups were either handled daily for 1 min during the first 10 days of life or left undisturbed. At the age of 90 days, a vaginal smear was collected daily at 9:00 a.m. and analyzed for 29 days; at 9:00 a.m. on the day of estrus, animals were anesthetized with thiopental (40 mg/kg, ip), the ovaries were removed and the oviduct was dissected and squashed between 2 glass slides. The number of oocytes of both oviductal ampullae was counted under the microscope. The average numbers for each phase of the cycle (diestrus I, diestrus II, proestrus and estrus) during the period analyzed were compared between the two groups. There were no significant differences between intact and handled females during any of the phases. However, the number of handled females that showed anovulatory cycles (8 out of 11) was significantly higher than in the intact group (none out of 10). Neonatal stimulation may affect not only the hypothalamus-pituitary-adrenal axis, as previously demonstrated, but also the hypothalamus-pituitary-gonadal axis in female rats

Aspectos básicos de la neuroendocrinoinmunología (NEI) / Basic aspects of the neuroendocrinoimmunology

En este artículo se discuten los aspectos básicos de la interacción entre los sistemas neuroendócrino e inmune. Existen dos vías principales de comunicación ente el cerebro y el sistema inmune: el sistema nervioso autónomo y la rama neuroendócrina a través de los productos que libera la pituitaria. La pincipal influencia del cerebro sobre la función inmune es ejercida a través del eje hipotálamo-pituitaria adrenal (HPA). Ciertos neurotransmisores, neuropéptidos y neurohormonas afectan la función inmune tanto in vivo como in vitro. Además, las células inmunes expresan en sua membranas receptores para esas moléculas. Una característica de esta comunicación es su bidireccionalidad ya que las citoquinas que se producen y liberan durante la respuesta inmune pueden a su vez, afectar al eje HPA. En este contexto, describimos parte de nuestro trabajo experimental desarrolado en ratas infectadas com Candida albicans y expuestas a un esquema de estrés crónico y variado.

Cortisol response to arginine-vasopressin does not compare with cortisol response to insulin-hypoglycemia in pituitary tumors.

Timed cortisol responses to insulin-hypoglycemia (IH) and arginine-vasopressin (AVP) were compared in 16 patients with pituitary tumors and six healthy controls. Serum cortisol was estimated by a specific and sensitive radioimmunoassay as per the WHO protocol. The basal cortisol (AM) was normal (> 290 nmol/l) in 9 patients and low in seven. With IH peak cortisol response was normal (> 550 nmol/l) in 10 patients, 8 of whom had normal and 2 had low basal (AM) cortisol. In contrast AVP evoked normal cortisol responses in only 5 of these patients, all of whom had normal basal (AM) cortisol and none had low basal (AM) cortisol. The data indicate lower sensitivity for AVP stimulation test (50%) and favour IH as the standard cortisol stimulation test in patients with pituitary tumors awaiting surgery.

Food and the circadian activity of the hypothalamic-pituitary-adrenal axis

Temporal organization is an important feature of biological systems and its main function is to facilitate adaptation of the organism to the environment. The daily variation of biological variables arises form an internal time-keeping system. The major action of the environment is to synchronize the internal clock to a period of exactly 24 h. The lightdark cycle, food ingestion, barometric pressure, acoustic stimuli, scents and social cues have been mentioned as synchronizers or "zeitgebers". The circadian rhythmicity of plasma corticosteroids has been well characterized in man and in rats and evidence has been accumulated showing daily rhythmicity at every level of the hypothalamic-pituitary-adrenal (HPA) axis. Studies of restricted feeding in rats are of considerable importance because they reveal feeding as a major synchronizer of rhythms in HPA axis activity. The daily variation of the HPA axis stress response appears to be closely related to food intake as well as to basal activity. In humans, the association of feeding and HPA axis activity has been studied under physiological and pathological conditions such as anorexia nervosa, bulimia, malnutrition, obesity, diabetes mellitus and Cushing's syndrome. Complex neuroanatomical pathways and neurochemical circuitry are involved in feeding-associated HPA axis modulation. In the present review we focus on the interaction among HPA axis rhythmicity, food ingestion, and different nutritional and endocrine states.