[Prognostic factors of live-birth after in vitro fertilization for unexplained infertility: A cohort study]. / Facteurs pronostiques des chances de naissance vivante en fécondation in vitro pour infertilité inexpliquée : étude de cohorte.

OBJECTIVES: For 15 to 30% of infertile couples, no etiology can be found, leading to the diagnosis of "unexplained infertility". The aim of our study was to identify prognostic factors for live birth following in vitro fertilization (IVF) for these couples. METHODS: A retrospective, monocentric study on a cohort of couples undergoing IVF for unexplained infertility with the woman aged≤40 years old. Primary analysis compared couples with a live birth following IVF versus childless couples following IVF. RESULTS: Between January 2014 and December 2018, 104 couples were included, 196 transvaginal oocyte pickup were performed, followed by 234 embryo transfers (fresh or cryopreserved) which resulted in 43 deliveries. The cumulative live birth rate was 40.4% per couple. Before IVF attempts, no clinical or paraclinical prognostic factors between the two groups was observed. However, multivariate analysis showed several biological factors of good prognosis in course of treatment, such as a higher number of mature oocytes and better quality embryos in "live birth" group. CONCLUSIONS: For a couple, the chances of having a child following IVF unexplained infertility are 40.4%. However, no clinical characteristic enabled us to identify favourable or unfavourable prognosis factors before starting ART. The prognostic factors identified during IVF cycle are interesting to advise or not to pursue IVF.

No specific adverse pregnancy outcome in singleton pregnancies after assisted reproductive technology (ART) for unexplained infertility.

OBJECTIVE: To evaluate the obstetrical outcome of pregnancies obtained after assisted reproductive technology (ART).in women with unexplained infertility. MATERIALS AND METHODS: We conducted a retrospective observational case - control cohort study between January 2011 and May 2017. All pregnancies obtained after ART (Intra uterine insemination, In Vitro Fertilization, Intra Cytoplasmic Sperm Injection) were included. The ART pregnancy outcome of women with unexplained infertility was compared to ART pregnancies obtained in a context of male infertility. Cases were matched to controls (1:2) for age, Body Mass Index (BMI), and smoking status. RESULTS: After exclusion of twins, we studied 67 singleton pregnancies in the case group, matched with 129 singleton pregnancies in the control group. The first-trimester complications (miscarriage before 12 weeks gestation (WG), ectopic pregnancy) were similar in the two groups. Concerning the 2nd and the 3rd trimester, the incidence of gestational diabetes mellitus, pre-eclampsia, placenta previa, preterm labor was comparable between the two groups. In singletons, we found a non-significant increase of post-partum hemorrhage (OR=5.5, IC 0.5-50, p=0.13) and small for gestational age new-borns (OR=3.45, IC 0.65-18.1, p=0.14) in women with unexplained infertility. CONCLUSION: More adverse obstetrical outcome are commonly reported after ART, even in singleton pregnancies. Little is known for explaining it and to distingue the own contributions of ART techniques and of the infertility etiology. In our study, we didn't observe a significant negative impact of a history of unexplained infertility on pregnancy. However, further large studies are needed to evaluate more accurately the possible liabilities of the infertility etiology on obstetrical and perinatal outcome.

[Elective single embryo transfer policy at 48/72 h: which results after fresh transfers and frozen/thawed transfers?]. / Politique de transfert électif d'un embryon à 48/72h: quels résultats après transferts frais et transferts d'embryons congelés ?

OBJECTIVES: To evaluate our elective single embryo transfer policy performed at 48/72h and define predictive factors of pregnancy after frozen/thawed embryo transfer. METHODS: Analysis of 289 elective single embryo transfers (eSET) performed in a selected population in the ART center of Marseille University Hospital from January 2005 to December 2011, as well as the 325 following frozen/thawed embryo transfers performed in this population between May 2005 and December 2012. RESULTS: Cumulative pregnancy rate/oocyte retrieval was of 62.6%; 45% of the couples obtained the birth of at least one child. During this studied period, cumulative pregnancy and delivery rates in the whole population remained stable while multiple delivery rate/delivery clearly decreased. Elective single embryo after frozen/thawed transfer gave satisfying results (24.6% pregnancy/transfer) only in the lack of lysis or in case of mild lysis (1-25%) of the transferred embryo. CONCLUSION: The implementation of an eSET policy gives satisfying results, depending largely on embryo quality. By proposing eSET to a well-targeted population, chosen both on clinical and biological criteria, a clear reduction of cumulative multiple delivery rate/delivery was obtained in our center over this period, without any global decrease of cumulative pregnancy rate/attempt. Embryo quality is a major factor of success, especially in frozen/thawed cycles. The elective single embryo frozen/thawed transfer should be carried out only if embryo lysis after thawing does not exceed 25%.

[Macrocephalic spermatozoa. What would be the impact on reproduction?]. / Les spermatozoïdes macrocéphales. Quels risques pour la fonction de reproduction ?

OBJECTIVE: We want to highlight the risk of infertility and failure of Assisted Reproductive Technologies due to the presence of macrocephalic spermatozoa (MS) in the sperm at rate equalling or superior to 20% in at least one semen analysis. PATIENTS AND METHODS: We did a retrospective analysis of 19 infertile patients presenting MS at average rate between 14.3 and 49.7%. For each patient, at least one semen analysis showed a MS rate equal or superior to 20%. We did an automated analysis of the spermatozoa surface for 13 patients and a detailed analysis of the MS morphology in 18 patients. Thirteen couples benefited of one or more IVF with or without ICSI. RESULTS: The semen analysis shows an impairment of one or more parameter of the sperm in all patients. Three morphological aspects for MS were highlighted: MS with irregular head, MS with regular head, and MS with multiple heads, with a dominance of irregular heads. The spermatozoa surface analysis shows a significant increase of the average surface and of the standard deviation (p<0.0001). The average rate of pregnancies by transfer is decreased compared to usual rates in our laboratories (13% versus 28%). DISCUSSION AND CONCLUSION: We want to sensitize biologist and clinical doctors to the existence of partial forms of this syndrome, which could be related to infertility with impaired sperm parameters and low pregnancy rates after FIV or ICSI.

[Genetic aspects of the teratozoospermia]. / Aspects génétiques de la tératozoospermie.

Recent mutation identification in well-known sperm defects gives proof that there are genetic causes of infertility. Familial forms and some features of the spermograms lead toward the genetic origin of these syndromes. For each syndrome, several clinical aspects and partial forms were described. In these latter, apparently normal spermatozoa coexist with those showing the phenotype of interest. Transmission electron microscopy is the better tool to characterize the specific details of each syndrome. The frequency of genetic teratozoospermia is weak, the most studied syndromes are the globozoospermia, the macrocephaly, the syndrome of decapitated spermatozoa and the dyplasia of the fibrous sheat. A mutation was identified for two from these syndromes, but the two mutations does not account for all the cases from each syndrome. The various clinical aspects observed for each syndrome suggest that either other mutations or other genes are probably involved in these spermatogenic failures. The use of spermatozoa from patients for intra cytoplasmic sperm injection (ICSI) may pose two problems: fertilization problems and genetic risk for the progeny, including chromosomic and genic risk. Except for total macrocephaly which is excluded from ICSI because of sperm chromosomal abnormalities, these syndromes are consistent with assisted fertilization, but with uncertain rates of fertilization and pregnancy.

The inflammatory receptor CD40 is expressed on human adipocytes: contribution to crosstalk between lymphocytes and adipocytes.

AIMS/HYPOTHESIS: Obesity is associated with adipose tissue inflammation. The CD40 molecule, TNF receptor superfamily member 5 (CD40)/CD40 ligand (CD40L) pathway plays a role in the onset and maintenance of the inflammatory reaction, but has not been studied in human adipose tissue. Our aim was to examine CD40 expression by human adipocytes and its participation in adipose tissue inflammation. METHODS: CD40 expression was investigated in human whole adipose tissue and during adipocyte differentiation by real-time PCR, Western blot and immunohistochemistry. The CD40/CD40L pathway was studied using recombinant CD40L (rCD40L) in adipocyte culture and neutralising antibodies in lymphocyte/adipocyte co-culture. RESULTS: CD40 mRNA levels in subcutaneous adipose tissue were higher in the adipocyte than in the stromal-vascular fraction. CD40 expression was upregulated during adipocyte differentiation. Addition of rCD40L to adipocytes induced mitogen activated protein kinase (MAPK) activation, stimulated inflammatory adipocytokine production, and decreased insulin-induced glucose transport in parallel with a downregulation of IRS1 and GLUT4 (also known as SCL2A4). rCD40L decreased the expression of lipogenic genes and increased lipolysis. CD40 mRNA levels were significantly higher in subcutaneous adipose tissue than in visceral adipose tissue of obese patients and were positively correlated with BMI, and with IL6 and leptin mRNA levels. Lymphocyte/adipocyte co-culture led to an upregulation of proinflammatory adipocytokines and a downregulation of leptin and adiponectin. Physical separation of the two cell types attenuated these effects, suggesting the involvement of a cell-cell contact. Blocking the CD40/CD40L interaction with neutralising antibodies reduced IL-6 secretion from adipocytes. CONCLUSIONS/INTERPRETATION: Adipocyte CD40 may contribute to obesity-related inflammation and insulin resistance. T lymphocytes regulate adipocytokine production through both the release of soluble factor(s) and heterotypic contact with adipocytes involving CD40.

Chronic plasminogen activator inhibitor-1 (PAI-1) overexpression dampens CD25+ lymphocyte recruitment after lipopolysaccharide endotoxemia in mouse lung.

BACKGROUND: Plasma plasminogen activator inhibitor-1 (PAI-1) level rises during sepsis and confers a worse prognosis. PAI-1 participation to sepsis has been poorly documented and was mainly associated with fibrin deposits. Beside fibrin deposits, increased tissue PAI-1 expression may contribute to the poor outcome of endotoxemia through other mechanisms. OBJECTIVE AND METHODS: During lipopolysaccharide (LPS) challenge, the role of PAI-1 in the early phase of inflammation was examined in the lungs of transgenic mice that either overexpress or lack the PAI-1 gene (PAI-1Tg or PAI-1(-/-)). RESULTS: Analysis of leukocytes revealed that neutrophil and macrophage infiltrations did not differ for PAI-1Tg and wild-type (WT) mice. Remarkably, CD25+ lymphocyte infiltration was totally blunted in PAI-1Tg lungs and inversely correlated with fibrin depositions. In parallel, mRNA levels of the regulatory T cell (Treg) markers FoxP3, CTLA-4, and GITR were significantly lower in PAI-1Tg than in WT lungs after LPS challenge. These data are supported by opposite results in PAI-1(-/-) lungs. The systemic compartments (spleen and peripheral blood) showed no decrease in CD25+, CD4+ CD25+ lymphocytes, and Treg markers in PAI-1Tg mice after LPS injection compared with WT mice. In addition, plasma and lung concentrations of interleukin-6 (IL-6) and macrophage inflammatory protein-1alpha (MIP-1alpha) were significantly higher in PAI-1Tg mice than WT mice. CONCLUSION: Our results suggest that chronic tissue PAI-1 overexpression influences the early phase of the inflammatory response during endotoxemia through the control of T lymphocyte traffic.

Expression of adrenomedullin in adipose tissue of lean and obese women.

OBJECTIVE: Adrenomedullin (AM), a potent vasodilatator and antioxidative peptide, was shown recently to be expressed by adipose tissue. The aim of our study was to investigate the precise localization of AM within human adipose tissue, and to examine AM regulation in obesity. DESIGN: Subcutaneous (SC) and omental (OM) adipose tissues from 9 lean and 13 obese women were profiled for AM expression changes. Preadipocytes from human adipose tissue were isolated and differentiated under defined adipogenic conditions. METHODS: AM expression was analyzed by immunohistochemistry, in situ hybridization and quantitative RT-PCR. RESULTS: A strong AM expression was observed in vessel walls, stromal cell clusters and isolated stromal cells, some of them being CD 68 positive, whereas mature adipocytes were not labeled. Calcitonin receptor-like receptor and receptor activity-modifying proteins (RAMP) 2 and RAMP 3 were expressed in vessel walls. In vitro, preadipocytes of early differentiation stages spontaneously secreted AM. No difference in AM localization was found between SC and OM adipose tissue. AM levels in SC tissue did not differ between lean and obese subjects. By contrast, AM levels in OM tissue were significantly higher in obese as compared with lean women. Moreover, we found a positive relationship between OM AM and tumor necrosis factor alpha mRNA levels and AM-immunoreactive area in OM tissue followed the features of the metabolic syndrome. CONCLUSION: Stromal cells from human adipose tissue, including macrophages, produce AM. Its synthesis increased in the OM territory during obesity and paralleled the features of the metabolic syndrome. Therefore, AM should be considered as a new member of the adipokine family.

11beta-Hydroxysteroid dehydrogenase type 1-driven cortisone reactivation regulates plasminogen activator inhibitor type 1 in adipose tissue of obese women.

BACKGROUND: Plasminogen activator inhibitor type 1 (PAI-1) is the main inhibitor of the fibrinolytic system and contributes to an increased risk of atherothrombosis in insulin-resistant obese patients. In adipose tissue, we have shown that PAI-1 is synthesized mainly in the visceral stromal compartment and is positively regulated by glucocorticoids. We have demonstrated that adipose tissue expression of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1), an enzyme that catalyzes the conversion of inactive cortisone to active cortisol, is exaggerated in obese patients. OBJECTIVES: We hypothesized that increased action of 11beta-HSD-1 in adipose tissue of obese subjects may contribute to PAI-1 overproduction. PATIENTS AND METHODS: Using in situ hybridization, we studied the expression of the mRNAs coding for PAI-1 and 11beta-HSD-1 in the stromal compartment of visceral adipose tissue obtained from obese women. The regulation of PAI-1 secretion from in vitro incubated tissue explants was also investigated. RESULTS: Regression analysis showed a significant positive linear relationship between PAI-1 and 11beta-HSD-1 mRNAs expression. In vitro incubation of adipose tissue explants demonstrated that cortisone stimulated PAI-1 gene expression and secretion, and that these effects were inhibited by co-incubation with the 11beta-HSD inhibitor, glycyrrhetinic acid. CONCLUSIONS: Our data demonstrate that 11beta-HSD-1-driven cortisone reactivation regulates adipose PAI-1 synthesis and secretion. They suggest that the increased PAI-1 synthesis and secretion observed in obese patients can be also related, at least in part, to an increased local conversion of cortisone to cortisol. Therefore, local cortisol metabolism in adipose tissue may be involved in increasing the risk of cardiovascular disease in obese subjects.

[Optimization of artificial inseminations with donor semen: a four-year experience]. / Optimisation des résultats d'inséminations intra-utérines uniques avec sperme de donneur: bilan de quatre ans d'activité.

OBJECTIVE: Our aim was to analyse the results of a donor insemination program using ovarian stimulation, swim-up sperm preparation and intrauterine insemination proposed to women with a maximum age of 39. Incidence of several clinical and biological parameters on success rates was investigated. PATIENTS AND METHODS: Retrospective analysis of the results of 249 cycles performed in 106 couples during a four-year period is reported. RESULTS: Overall pregnancy rate of 28.1% and delivery rate of 22% per cycle were achieved, with a multiple pregnancy rate of 11.4%. Most of the pregnancies (84%) were obtained before the fourth insemination. Among the different parameters studied the total number of motile sperm inseminated was found to be the most important factor for success rate: pregnancy rate per cycle reached 40.4% if more than 1.5 million progressive sperm were inseminated vs. 24.7% if they were less than 1.5 million (P<0.05). DISCUSSION AND CONCLUSION: In precise conditions, outcome of inseminations with donor semen can reach satisfying pregnancy rates, being a valuable help for couples suffering of long-time infertility.

[Pregnancy outcome and the status of the newborn infant after ICSI at La Conception Hospital in Marseille]. / Evolution des grossesses et état des enfants à la naissance après ICSI à l'hôpital de La Conception à Marseille.

OBJECTIVE: To evaluate obstetric outcome of pregnancies and pediatric follow-up of children born after ICSI procedure. MATERIAL AND METHOD: Prospective study from october 1994 to September 1998 in medical assisted procreations center in La Conception hospital in Marseilles. Three hundred forty-two couples undergoing ICSI procedures. INTERVENTIONS: analysis of pregnancy rates, prematurity rates, obstetric outcome and frequency of congenital malformations. RESULTS: One hundred seventy-eight pregnancies have been obtained with 111 children. Multiple pregnancy rate arise 29.7%. The average term at birth in the singleton pregnancies (38.7 weeks) is higher than in the twins (35.7 weeks). The prematurity rate of delivery before 35 weeks of gestation is about 9.6%. Seven of 111 neonates was born with a congenital malformation, no cardiovascular one. One of boys presents a bilateral cryptorchidism with severe bilateral hypotrophy. CONCLUSIONS: Our results are similar with those of others teams. Congenital malformation rates is near rates reported in others studies. However, no bilateral cryptorchidism with bilateral severe hypotrophy has been yet reported in literature.

[Intrauterine insemination with the husband's sperm: conclusions of five years experience]. / Inséminations intra-utérines avec sperme du conjoint (IIU-AC): conclusions de 5 ans d'expérience.

We analyzed retrospectively 936 intrauterine insemination (IUI) cycles with husband's sperm (384 couples). Superovulation and induction monitoring occurred in the majority of cases; IUI was timed 36-40 h after ovulatory hCG. The overall pregnancy rate per cycle (PR/C) was 11.4% (107/936). Data analysis demonstrated that PR/C decreased with infertility duration, woman's age (especially after 38 years old) and number of attempts (significantly after the 4 th cycle). Superovulation (in particular by antiestrogens) and induction monitoring seemed to provide an increase in cycle pregnancy rate. Highest PR/C were observed in dysovulation and male infertility groups. In cases of sperm defects, our data showed that 2 parameters had a significant influence on pregnancy outcome: the number of motile progressive inseminated spermatozoa (> 300,000) and the spermatozoa survival rate after 24 h (> 50%). As a conclusion, intrauterine insemination can be proposed as a satisfying treatment of infertility, if precise protocol is followed and its indications well-defined.

The modulatory role of estrogens on corticotropin-releasing factor gene expression in the hypothalamic paraventricular nucleus of ovariectomized rats: role of the adrenal gland.

In vitro, estrogens stimulate corticotropin-releasing factor (CRF) gene transcription. In ovariectomized (OVX) rats, estrogens have a negative effect on CRF mRNA levels in the hypothalamic paraventricular nucleus. This suggests that the stimulatory influence of estrogens found in vitro may be masked in vivo by an inhibitory effect mediated through neural and/or humoral factors. Glucocorticoids may be involved in this phenomenon since estrogens increase circulating corticosterone levels in OVX rats. We studied the effect of 7-day 17 beta-estradiol (E2) treatment on CRF gene expression in the paraventricular nucleus of 2-week OVX mature rats after sham operation or adrenalectomy (ADX) with or without corticosterone replacement. In sham ADX animals, E2 administration increased plasma corticosterone concentrations, did not change the binding capacity or the affinity of circulating corticosteroid binding globulin, and decreased hypothalamic CRF gene expression. Following ADX, CRF mRNA levels increased and were normalized by corticosterone treatment. Estrogens induced a significant build up in CRF mRNA concentrations in both ADX or ADX corticosterone-replaced animals. Our data demonstrate that the positive effect of estrogens on CRF gene expression found in vitro or in vivo after ADX is antagonized, in vivo when the adrenal glands are intact, by a negative influence. They strongly suggest that the increased circulating corticosterone levels induced by E2 administration mediate the inhibitory effect of estrogens on CRF mRNA levels. These observations may explain the gender related differences in the basal and stress-induced hypothalamo-pituitary-adrenal activity.

[Regulation of corticotropic function in stressful situations]. / Régulation de la fonction corticotrope dans les situations de stress.

ACTH secretion is mainly controlled by two hypothalamic neurohormones: corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP). Both peptides are synthesized in the hypothalamic paraventricular nucleus (PVN) (in parvo-cellular neurons for CRH and in magnocellular neurons for most AVP). Under basal conditions, some CRH neurons coexpress AVP (CRH+/AVP+ neurons). This colocalisation represents a form of functional plasticity since the number of CRH+/AVP+ neurons increases after acute or repeated stress exposure. Experiments in sheep and rat (studies on the secretion of both peptides in hypophysial portal blood, effects of anti-CRH and anti-AVP immunisation upon ACTH secretion) indicate that stress-induced ACTH stimulation involves both CRH and AVP. Unlike CRH which participates also in the maintenance of basal ACTH and glucocorticoids secretion, the role of AVP appears to be limited to corticotropic response to stress.

Estrogens decrease expression of the corticotropin-releasing factor gene in the hypothalamic paraventricular nucleus and of the proopiomelanocortin gene in the anterior pituitary of ovariectomized rats.

It is known that estrogens modulate the hypothalamopituitary-adrenal (HPA) axis both under resting conditions and during exposure to stress. Nevertheless, the site of action of estrogens is not still fully elucidated. We sought to determine if estrogens could act on the major hypothalamic ACTH secretagogue: corticotropin-releasing factor (CRF). Mature rats were ovariectomized (OVX) and 2 weeks later implanted with silastic capsules containing 17ß-estradiol (E(2)). Animals were sacrificed 7 days later. CRF mRNA in the hypothalamic paraventricular nucleus (PVN) and proopiomelanocortin (POMC) mRNA in the anterior pituitary were measured byin situ hybridization. CRF content in the median eminence was measured by semiquantitative immunocytochemistry. E(2) treatment induced a significant decrease of CRF mRNA levels in the PVN (3.70±0.14vs 4.79±0.15 copies of probe×10(-3)/µm(3) of tissue in OVX rats,P<0.05), an accumulation of immunoreactive CRF in the zona externa of the median eminence (207±36vs 100±15% in OVX rats,P<0.05), and a decrease of POMC mRNA levels in the anterior pituitary (4.6±0.6vs 6.9±0.6 copies of probe ×10(-2)/µm(3) of tissue in OVX rats,P<0.05). These results demonstrate that estrogens have a negative effect on CRF gene expression and secretion and on POMC gene expression. Whether estrogens modulate directly the CRF-synthesizing cells or act through an increase of the glucocorticoid negative feedback remains to be determined.

Insulin-induced hypoglycaemia increases colocalization of corticotrophin-releasing factor and arginine vasopressin mRNAs in the rat hypothalamic paraventricular nucleus.

The regulation of ACTH secretion during stress is a multifactorial process that mainly involves two hypothalamic neurohormones: corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP). In this report we measured, using semiquantitative in situ hybridization, the concentrations of CRF and AVP mRNA in hypophyseotrophic paraventricular parvocellular cell bodies of male rats after an acute (3-h) exposure to insulin-induced hypoglycaemia. Insulin injection (2.5 IU/kg) induced a significant decrease in blood glucose levels and a strong increase in plasma ACTH concentrations. The concentration of CRF mRNA in the paraventricular nucleus (PVN) was significantly increased after insulin-induced hypoglycaemia (150% of control levels), while the number of CRF mRNA-containing cell bodies was not changed. Double-labelling experiments demonstrated that the number of CRF mRNA-containing cell bodies that also contained AVP mRNA was doubled after insulin injection. These data demonstrate that the established increased colocalization of AVP immunoreactivity in nerve terminals immunoreactive for CRF after exposure to stress follows a pretranslational activation of AVP synthesis. Cell-by-cell analysis indicated that the mean CRF hybridization signal was increased in double-labelled cells (about 150% of control levels), suggesting that the increase in CRF gene expression occurs equally in the AVP-synthesizing and in the AVP-deficient CRF mRNA-containing cell bodies. The mean AVP hybridization signal in the double-labelled cells was decreased, suggesting that the amount of AVP mRNA was unchanged in the cell bodies that expressed both CRF and AVP in the basal state and that AVP mRNA levels in the cell bodies recruited after insulin-induced hypoglycaemia were below control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of alpha 2-adrenoceptors stimulates basal and stress-induced adrenocorticotropin secretion in the developing rat through a central mechanism independent from corticotropin-releasing factor and arginine vasopressin.

In the neonatal rat, the response of the hypothalamo-pituitary-adrenal axis to stressful stimuli is markedly reduced during the first 2 weeks of life [stress-hyporesponsive period (SHRP)]. In this report, we studied the effect of idazoxan (an alpha 2-adrenergic antagonist) on plasma ACTH and corticosterone levels in 8-day-old rats. Indeed, it is known that in the adult rat, blockade of alpha 2-adrenoceptors increases ACTH secretion stimulated by CRF and arginine vasopressin (AVP) injection. Injection of 2.5 micrograms/g idazoxan induced a rapid (within 30 min) increase in basal plasma ACTH and corticosterone levels that lasted for 60 min. Injection of increasing doses of idazoxan led to a dose-dependent stimulation of ACTH and corticosterone levels. Administration of 2.5 micrograms/g idazoxan significantly increased the ACTH response to insulin-induced hypoglycemia, whereas it potentiated and accelerated the ACTH response to ether exposure stress. We next examined ACTH secretion from superfused anterior pituitary glands. Neither the alpha 2-adrenergic agonist clonidine nor idazoxan changed the basal ACTH secretory rate. Idazoxan had no effect on CRF- and AVP-stimulated ACTH secretion. This indicates that in vivo, idazoxan acts at a suprapituitary level. To investigate a possible effect of idazoxan on presynaptic alpha 2-adrenoceptors, we studied the effect of idazoxan on the concentrations of norepinephrine (NE) and L-DOPA in punches of locus coeruleus after dopa-decarboxylase blockade. Idazoxan injection induced a decrease in the NE content, without changing L-DOPA levels, indicating that idazoxan can act at the level of presynaptic alpha 2-adrenoceptors, inducing an increased release and/or degradation of NE without any effect on catecholamines synthesis. Finally, we investigated a possible involvement of CRF and AVP in mediating the effect of alpha 2-adrenoceptor blockade on ACTH secretion. Passive immunization against CRF or AVP did not change the ACTH response to idazoxan administration, whereas idazoxan pretreatment had simply an additive effect on CRF- and lysine vasopressin-stimulated ACTH secretion. In conclusion, our data demonstrate that during the SHRP, blockade of alpha 2-adrenoceptors induces an increase in both basal and stress-induced ACTH secretion. They suggest that a decreased catecholaminergic tone, consecutive to an increased occupation of alpha 2-adrenoceptors, acting through a central mechanism independent from CRF and AVP may be responsible for the SHRP in the developing rat.