Ketamine inhibits fetal ACTH responses to cerebral hypoperfusion

Acute adrenal necrosis in a young female cat

CASE DESCRIPTION

An 18-month-old spayed female domestic short haired cat was presented for poor appetite, lethargy, exaggerated swallowing, and regurgitation 2 weeks after endoscopic retrieval of gastric foreign material.

CLINICAL FINDINGS

The cat was quiet with tacky mucous membranes on physical examination. Point-of-care blood testing identified mild azotemia, moderate hypercalcemia, and a sodium-to-potassium ratio of 26. An ultrasound examination the next day identified moderate to marked bilateral adrenomegaly. Cytology of a fine needle aspirate of the adrenal glands was consistent with necrosis and associated inflammation. Hypoadrenocorticism was diagnosed by a confirmatory adrenocorticotropic hormone stimulation test.

TREATMENT AND OUTCOME

The cat normalized both clinically and biochemically after treatment with prednisolone and desoxycorticosterone pivalate.

CLINICAL RELEVANCE

Acute adrenal necrosis has been well documented in human medicine after anesthetic events. To our knowledge, hypoadrenocorticism caused by cytologically confirmed acute adrenal necrosis has not been previously reported in dogs and cats.

Transient effects of forebrain ischemia on fetal heart rate variability in fetal sheep

Fetal heart rate variability (FHRV) is a key index of antenatal and intrapartum fetal well-being. FHRV is well established to be mediated by both arms of the autonomic nervous system, but it remains unknown whether higher centers in the forebrain contribute to FHRV. We tested the hypothesis that selective forebrain ischemia would impair the generation of FHRV. Sixteen chronically instrumented near-term fetal sheep were subjected to either forebrain ischemia induced by bilateral carotid occlusion or sham-ischemia for 30 min. Time, frequency, and nonlinear measures of FHRV were assessed during and for seven days after ischemia. Ischemia was associated with profound suppression of electroencephalographic (EEG) power, which remained suppressed throughout the recovery period (P < 0.001). During the first 5 min of ischemia, multiple time and frequency domain measures were increased (all P < 0.05) before returning back to sham levels. A delayed increase in sample entropy was observed during ischemia (P < 0.05). For the first 3 h after ischemia, there was moderate suppression of two measures of FHRV (very-low frequency power and the standard deviation of RR-intervals, both P < 0.05) and increased sample entropy (P < 0.05). Thereafter, all measures of FHRV returned to control levels. In conclusion, profound forebrain ischemia sufficient to lead to severe neural injury had only transient effect on multiple measures of FHRV. These findings suggest that the forebrain makes a limited contribution to FHRV. FHRV therefore primarily originates in the hindbrain and is unlikely to provide meaningful information on forebrain neurodevelopment or metabolism.

Current paradigms and new perspectives on fetal hypoxia: implications for fetal brain development in late gestation

The availability of oxygen to the fetus is limited by the route taken by oxygen from the atmosphere to fetal tissues, aided or diminished by pregnancy-associated changes in maternal physiology and, ultimately, a function of atmospheric pressure and composition of the mother's inspired gas. Much of our understanding of the fetal physiological response to hypoxia comes from experiments designed to elucidate the cardiovascular and endocrine responses to transient hypoxia. Complementing this work is equally impactful research into the origins of intrauterine growth restriction in which animal models designed to restrict the transfer of oxygen from the maternal to the fetal circulation were used. A common assumption has been that outcomes measured after a period of hypoxia are related to cellular deprivation of oxygen and reoxygenation: an assumption based on a focus on what we can see "under the streetlights." Recent studies demonstrate that availability of oxygen may not tell the whole story. Transient hypoxia in the fetal sheep stimulates transcriptomics responses that mirror inflammation. This response is accompanied by the appearance of bacteria in the fetal brain and other tissues, likely resulting from a hypoxia-stimulated release of bacteria from the placenta. The appearance of bacteria in the fetus after transient hypoxia complements the recent discovery of bacterial DNA in the normal human placenta and in the tissues of fetal sheep. An understanding of the mechanism of the physiological, cellular, and molecular responses to hypoxia requires an appreciation of stimuli other than cellular oxygen deprivation: stimuli that we would have never known about without looking "between the streetlights," illuminating direct responses to the manipulated variables.

Ketamine Reduces Inflammation Pathways in the Hypothalamus and Hippocampus Following Transient Hypoxia in the Late-Gestation Fetal Sheep

The physiological response to hypoxia in the fetus has been extensively studied with regard to redistribution of fetal combined ventricular output and sparing of oxygen delivery to fetal brain and heart. Previously, we have shown that the fetal brain is capable of mounting changes in gene expression that are consistent with tissue inflammation. The present study was designed to use transcriptomics and systems biology modeling to test the hypothesis that ketamine reduces or prevents the upregulation of inflammation-related pathways in hypothalamus and hippocampus after transient hypoxic hypoxia. Chronically catheterized fetal sheep (122 ± 5 days gestation) were subjected to 30 min hypoxia (relative reduction in P_aO₂∼50%) caused by infusion of nitrogen into the inspired gas of the pregnant ewe. RNA was isolated from fetal hypothalamus and hippocampus collected 24 h after hypoxia, and was analyzed for gene expression using the Agilent 15.5 k ovine microarray. Ketamine, injected 10 min prior to hypoxia, reduced the cerebral immune response activation to the hypoxia in both brain regions. Genes both upregulated by hypoxia and downregulated by ketamine after hypoxia were significantly associated with gene ontology terms and KEGG pathways that are, themselves, associated with the tissue response to exposure to bacteria. We conclude that the results are consistent with interruption of the cellular response to bacteria by ketamine.

Ketamine modulates fetal hemodynamic and endocrine responses to umbilical cord occlusion

Umbilical cord occlusion (UCO) is a hypoxic insult that has been used to model birth asphyxia and umbilical cord compression in utero. UCO triggers vigorous neural and endocrine responses that include increased plasma ACTH and cortisol concentrations, increased blood pressure (BP), and decreased heart rate (HR). We have previously reported that ketamine, a noncompetitive N‐methyl‐D‐aspartate receptor antagonist, can modify the fetal hemodynamic and ACTH responses to ventilatory hypoxia and cerebral ischemia‐reperfusion. We performed the present experiments to test the hypothesis that ketamine has similar effects on the neuroendocrine and cardiovascular responses to UCO. Fetal sheep were chronically catheterized at gestational day 125. Ketamine (3 mg/kg) was administered intravenously to the fetus 10 min prior to the insult. UCO was induced for 30 min by reducing the umbilical vein blood flow until fetal P_aO₂ levels were reduced from 17 ± 1 to 11 ± 1 mm Hg. UCO produced an initial increase on fetal BP in both control and ketamine groups (P = 0.018 time), followed by a decrease in the control group, but values remained higher with ketamine. HR decreased after UCO (P = 0.041 stimulus*time) in both groups, but the reduction was greater initially in control compared to ketamine groups. Fetal P_aCO₂ levels increased after UCO (P < 0.01 stimulus*time), but values were higher in the control versus ketamine groups. UCO significantly decreased fetal pH values (P < 0.01 stimulus*time) with a greater effect on the control versus ketamine group. Ketamine delayed the cortisol responses to UCO (P < 0.001 stimulus*time), and UCO produced a robust increase in ACTH levels from 19 ± 2 to 280 ± 27 pg/mL (P < 0.001 stimulus*time), but there were no differences in ACTH levels between UCO groups. We conclude that ketamine augmented the cardiovascular response to UCO, but did not alter the ACTH response to UCO.

Ketamine suppresses hypoxia-induced inflammatory responses in the late-gestation ovine fetal kidney cortex

Acute fetal hypoxia is a form of fetal stress that stimulates renal vasoconstriction and ischaemia as a consequence of the physiological redistribution of combined ventricular output. Because of the potential ischaemia-reperfusion injury to the kidney, we hypothesized that it would respond to hypoxia with an increase in the expression of inflammatory genes, and that ketamine (an N-methyl-D-aspartate receptor antagonist) would reduce or block this response. Hypoxia was induced for 30 min in chronically catheterized fetal sheep (125 ± 3 days), with or without ketamine (3 mg kg(-1)) administered intravenously to the fetus 10 min prior to hypoxia. Gene expression in fetal kidney cortex collected 24 h after the onset of hypoxia was analysed using ovine Agilent 15.5k array and validated with qPCR and immunohistochemistry in four groups of ewes: normoxic control, normoxia + ketamine, hypoxic control and hypoxia + ketamine (n = 3-4 per group). Significant differences in gene expression between groups were determined with t-statistics using the limma package for R (P ≤ 0.05). Enriched biological processes for the 427 upregulated genes were immune and inflammatory responses and for the 946 downregulated genes were metabolic processes. Ketamine countered the effects of hypoxia on upregulated immune/inflammatory responses as well as the downregulated metabolic responses. We conclude that our transcriptomics modelling predicts that hypoxia activates inflammatory pathways and reduces metabolism in the fetal kidney cortex, and ketamine blocks or ameliorates this response. The results suggest that ketamine may have therapeutic potential for protection from ischaemic renal damage.

Ketamine Attenuates the ACTH Response to Hypoxia in Late-Gestation Ovine Fetus

BACKGROUND

Ketamine, a noncompetitive N-Methyl-D-aspartate (NMDA) receptor antagonist, is a commonly used dissociative anesthetic in neonatology. We have proposed that ketamine reduces fetal stress responsiveness to stimuli that involve reduced oxygen supply to the fetal brain. Previously, we have shown that ketamine inhibits plasma ACTH levels in late-gestation fetal sheep subjected to brachiocephalic artery occlusion (BCO), an ischemic hypoxia model that might activate some of the same direct and reflex responses as hypoxia.

OBJECTIVES

We performed the current study to test the hypothesis that ketamine pretreatment will reduce fetal ACTH responses to hypoxic hypoxia (HH).

METHODS

Fetal sheep were chronically catheterized at least 5 days prior to study. Ketamine (3 mg/kg) was administered intravenously to the fetus 10 min prior to normoxia or a period of hypoxia induced by administration of nitrogen gas to the maternal trachea for 30 min.

RESULTS

Hypoxia significantly increased both fetal ACTH and cortisol levels in both the control and ketamine groups (p < 0.0005, interaction effect of time·stimulus in two-way ANOVA), and the ACTH response was blunted by ketamine (p < 0.005).

CONCLUSIONS

Ketamine reduced fetal ACTH responses to HH, possibly due to antagonism of the NMDA receptors in the fetal brain. Interestingly, in contrast to the responses to BCO, ACTH responses to HH were only partially inhibited, suggesting that multiple neurotransmitter pathways mediate the ACTH response to HH.

Transcriptomics of the fetal hypothalamic response to brachiocephalic occlusion and estradiol treatment

Estradiol (E2) is a well-known modulator of fetal neuroendocrine activity and has been proposed as a critical endocrine signal readying the fetus for birth and postnatal life. To investigate the modulatory role of E2 on fetal stress responsiveness and the response of the fetal brain to asphyxic stress, we subjected chronically catheterized fetal sheep to a transient (10 min) brachiocephalic artery occlusion (BCO) or sham occlusion. Half of the fetuses received subcutaneous pellets that increased plasma E2 concentrations within the physiological range. Hypothalamic mRNA was analyzed using the Agilent 8x15k ovine array (019921), processed and annotated as previously reported by our laboratory. Analysis of the data by ANOVA revealed that E2 differentially regulated (DR) 561 genes, and BCO DR 894 genes compared with control and E2+BCO DR 1,153 genes compared with BCO alone (all P < 0.05). E2 upregulated epigenetic pathways and downregulated local steroid biosynthesis but did not significantly involve genes known to directly respond to the estrogen receptor. Brachiocephalic occlusion upregulated kinase pathways as well as genes associated with lymphocyte infiltration into the brain and downregulated neuropeptide synthesis. E2 upregulated immune- and apoptosis-related pathways after BCO and reduced kinase and epigenetic pathway responses to the BCO. Responses to BCO are different from responses to hypoxic hypoxia suggesting that mechanisms of responses to these two forms of brain hypoxia are distinct. We conclude that cerebral ischemia caused by BCO might stimulate lymphocyte infiltration into the brain and that this response appears to be modified by estradiol.

Estrogen in the fetus

Estradiol and other estrogens are important modulators of fetal and maternal physiology in pregnancy. Much is known about the biosynthesis of estrogens in fetus and mother, and much is known about the role that estrogen plays in labor and delivery. However, much less is known about the regulation of estrogen biosynthesis throughout the latter half of gestation, and the role that estrogen plays in homeostatic and neuroendocrine control in the fetus. This review focuses on the biosynthesis and actions of estrogen in the fetal circulation, the role that it plays in the development of the fetus in the latter half of gestation, and the role that is played by the estrogen milieu in the control of the timing of birth. Estrogen circulates in fetal blood in both unconjugated and conjugated molecular forms, with the conjugated steroids far more abundant than the unconjugated steroids. This review therefore also addresses the biological significance of the variety of molecular forms of estrogen circulating in fetal and maternal blood.

Hemodynamic and metabolic correlates of perinatal white matter injury severity

Background and Purpose

Although the spectrum of perinatal white matter injury (WMI) in preterm infants is shifting from cystic encephalomalacia to milder forms of WMI, the factors that contribute to this changing spectrum are unclear. We hypothesized that the variability in WMI quantified by immunohistochemical markers of inflammation could be correlated with the severity of impaired blood oxygen, glucose and lactate.

Methods

We employed a preterm fetal sheep model of in utero moderate hypoxemia and global severe but not complete cerebral ischemia that reproduces the spectrum of human WMI.

Since there is small but measurable residual brain blood flow during occlusion, we sought to determine if the metabolic state of the residual arterial blood was associated with severity of WMI. Near the conclusion of hypoxia-ischemia, we recorded cephalic arterial blood pressure, blood oxygen, glucose and lactate levels. To define the spectrum of WMI, an ordinal WMI rating scale was compared against an unbiased quantitative image analysis protocol that provided continuous histo-pathological outcome measures for astrogliosis and microgliosis derived from the entire white matter.

Results

A spectrum of WMI was observed that ranged from diffuse non-necrotic lesions to more severe injury that comprised discrete foci of microscopic or macroscopic necrosis. Residual arterial pressure, oxygen content and blood glucose displayed a significant inverse association with WMI and lactate concentrations were directly related. Elevated glucose levels were the most significantly associated with less severe WMI.

Conclusions

Our results suggest that under conditions of hypoxemia and severe cephalic hypotension, WMI severity measured using unbiased immunohistochemical measurements correlated with several physiologic parameters, including glucose, which may be a useful marker of fetal response to hypoxia or provide protection against energy failure and more severe WMI.

Genomics of the fetal hypothalamic cellular response to transient hypoxia: endocrine, immune, and metabolic responses

Fetuses respond to transient hypoxia (a common stressor in utero) with cellular responses that are appropriate for promoting survival of the fetus. The present experiment was performed to identify the acute genomic responses of the fetal hypothalamus to transient hypoxia. Three fetal sheep were exposed to 30 min of hypoxia and hypothalamic mRNA extracted from samples collected 30 min after return to normoxia. These samples were compared with those from four normoxic control fetuses by the Agilent 019921 ovine array. Differentially regulated genes were analyzed by network analysis and by gene ontology analysis, identifying statistically significant overrepresentation of biological processes. Real-time PCR of selected genes supported the validity of the array data. Hypoxia induced increased expression of genes involved in response to oxygen stimulus, RNA splicing, antiapoptosis, vascular smooth muscle proliferation, and positive regulation of Notch receptor target. Downregulated genes were involved in metabolism, antigen receptor-mediated immunity, macromolecular complex assembly, S-phase, translation elongation, RNA splicing, protein transport, and posttranscriptional regulation. We conclude that these results emphasize that the cellular response to hypoxia involves reduced metabolism, the involvement of the fetal immune system, and the importance of glucocorticoid signaling.

Chemoreflex activity increases prostaglandin endoperoxide synthase mRNA expression in the late-gestation fetal sheep brain

Fetal sheep defend blood pressure, blood volume, and blood gases using baro- and chemoreflexes that influence autonomic and neuroendocrine responses. The local generation of prostanoids within the fetal brain is also an important component in activating hormone responses to these stimuli, but the relationship between the reflexes and prostanoid biosynthesis is unclear. The present study was performed to test the hypothesis that the abundances of prostaglandin biosynthetic enzymes in the fetal brain are dependent upon the activity of the baro- and chemoreflex pathways. We subjected chronically catheterized fetal sheep in late gestation to a 10-minute period of brachiocephalic occlusion (BCO), a stimulus that provokes brisk cardiovascular and neuroendocrine responses. We compared the central nervous system abundance of prostaglandin endoperoxide synthases 1 and 2 (PGHS-1 and PGHS-2) after BCO to (1) fetal sheep that had been subjected to BCO after chronic sinoaortic denervation plus bilateral vagotomy and (2) fetal sheep in which the N-methyl d-aspartate (NMDA) receptor antagonist, ketamine, had been administered prior to BCO. Abundances of messenger RNA (mRNA) for PGHS-1 and of mRNA and protein for PGHS-2 in fetal hippocampus were reduced significantly by either prior denervation or ketamine administration. Prostaglandin endoperoxide synthases 1 and 2 mRNA in pituitary were decreased and increased, respectively, by ketamine pretreatment. The results of this study are consistent with the conclusion that the expression of PGHS-1 and -2 in fetal hippocampus and pituitary are influenced by the baro- and/or chemoreflex pathways within the fetal brain in late gestation.

Influence of estradiol and fetal stress on luteinizing hormone, follicle-stimulating hormone, and prolactin in late-gestation fetal sheep

BACKGROUND

Hypotension and reduced cerebral blood flow secondary to brachiocephalic occlusion (BCO) stimulate various homeostatic physiological and endocrine responses. Our previous studies have also suggested a role of estradiol in augmenting the fetal stress response to BCO.

OBJECTIVES

We tested the hypothesis that gonadotropins and/or prolactin (PRL) are upregulated in fetal pituitary in response to fetal stress and play a role in the response to BCO-induced stress.

METHODS

We performed 3 studies: one in which we measured ovine fetal pituitary PRL, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) mRNA throughout the latter half of gestation in order to better understand the ontogenetic changes upon which dynamic responses are superimposed; one in which we measured these mRNA abundances in response to BCO and/or estrogen treatment, and one in which we measured plasma LH responses to BCO in chronically catheterized late-gestation fetal sheep.

RESULTS

PRL gene expression is increased dramatically in the last 20% of gestation. LH and FSH mRNAs were unchanged except for a transient dip in the expression of LH in the last few days before the normal time of spontaneous parturition. Chronic treatment with estradiol decreased LH and FSH mRNA, but increased PRL mRNA abundance after BCO. In contrast, BCO alone increases the abundance of LH, but not FSH or PRL mRNA in fetal pituitary. Plasma LH concentrations were not increased in response to BCO.

CONCLUSIONS

We conclude that the late-gestation fetal sheep responds to hypotensive stress with increases in LH mRNA but not LH secretion. LH, FSH and PRL changes are therefore unlikely to contribute to the fetal response to cerebral hypoperfusion.

Interaction of PGHS-2 and glutamatergic mechanisms controlling the ovine fetal hypothalamus-pituitary-adrenal axis

Prostaglandins, generated within the fetal brain, are integral components of the mechanism controlling the fetal hypothalamus-pituitary-adrenal (HPA) axis. Previous studies in this laboratory demonstrated that prostaglandin G/H synthase isozyme 2 (PGHS-2) inhibition reduces the fetal HPA axis response to cerebral hypoperfusion, blocks the preparturient rise in fetal plasma ACTH concentration, and delays parturition. We also discovered that blockade of N-methyl-d-aspartate (NMDA) receptors reduces the fetal ACTH response to cerebral hypoperfusion. The present study was designed to test the hypothesis that PGHS-2 action and the downstream effect of HPA axis stimulation are stimulated by NMDA-mediated glutamatergic neurotransmission. Chronically catheterized late-gestation fetal sheep (n = 8) were injected with NMDA (1 mg iv). All responded with increases in fetal plasma ACTH and cortisol concentrations. Pretreatment with resveratrol (100 mg iv, n = 5), a specific inhibitor of PGHS-1, did not alter the magnitude of the HPA axis response to NMDA. Pretreatment with nimesulide (10 mg iv, n = 6), a specific inhibitor of PGHS-2, significantly reduced the HPA axis response to NMDA. To further explore this interaction, we injected NMDA in six chronically catheterized fetal sheep that were chronically infused with nimesulide (n = 6) at a rate of 1 mg/day into the lateral cerebral ventricle for 5-7 days. In this group, there was no significant ACTH response to NMDA. Finally, we tested whether the HPA axis response to prostaglandin E(2) (PGE(2)) is mediated by NMDA receptors. Seven chronically catheterized late-gestation fetal sheep were injected with 100 ng of PGE(2), which significantly increased fetal plasma ACTH and cortisol concentrations. Pretreatment with ketamine (10 mg iv), an NMDA antagonist, did not alter the ACTH or cortisol response to PGE(2). We conclude that generation of prostanoids via the action of PGHS-2 in the fetal brain augments the fetal HPA axis response to NMDA-mediated glutamatergic stimulation.

TPH2 5'- and 3'-regulatory polymorphisms are differentially associated with HPA axis function and self-injurious behavior in rhesus monkeys

Tryptophan hydroxylase-2 (TPH2) synthesizes neuronal serotonin and is linked to numerous behavioral traits. We have previously characterized the functionality of polymorphisms (especially 2051A>C) in 3'-untranslated region (3'-UTR) of rhesus monkey TPH2 (rhTPH2). This study further assessed the functionality of additional polymorphisms (-1605T>C, -1491Tn, -1485(AT)n, -1454A>G, -1325In>Del and -363T>G) in rhTPH2 5'-flanking region (5'-FR), and evaluated the effects of rhTPH2 5' and 3' genotypes on central serotonin turnover, hypothalamic-pituitary-adrenal (HPA) axis function and self-injurious behavior (SIB) in 32 unrelated adult male monkeys of Indian origin. Haplotypes of the rhTPH2 5'-FR polymorphisms exert a significant, cell-dependent effect on reporter gene expression, primarily conferred by -1485(AT)n. The -1485(AT)n and 2051A>C polymorphisms interact to influence cerebrospinal fluid (CSF) 5-HIAA and plasma adrenocorticotropic hormone (ACTH) in the afternoon. While -1485(AT)n exerts significant main effects on the afternoon cortisol level and nocturnal HPA negative feedback, 2051A>C has significant main effects on the morning cortisol level and cortisol response to ACTH challenge, as well as marginally significant main effects on the daytime HPA negative feedback and self-biting rate. In addition, the genotype/allele frequency of the 5'-FR -1325Ins>Del differed significantly between the self-wounders and non-wounders, whereas 3'-UTR 2128S>L polymorphism differed significantly in genotype/allele frequency between the high- and low-frequency biters. This study shows the functionality of rhTPH2 5'-FR polymorphisms, and provides evidence for the differential association of rhTPH2 5'-FR and 3'-UTR polymorphisms with HPA axis function and SIB. Our findings shed light on the role of TPH2 gene variance in physiology and behavioral traits, and also contribute to the understanding of the pathophysiology and genetics of SIB.

Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus

Decreases in fetal blood pressure stimulate homeostatic stress responses that help return blood pressure to normal levels. Fetal hypothalamus-pituitary-adrenal (HPA) axis responses to hypotension are mediated by chemoreceptor and baroreceptor reflexes and ischemia of the fetal central nervous system. Indomethacin, a nonselective inhibitor of prostaglandin endoperoxide synthase (PGHS)-1 and -2, attenuates the HPA response to hypotension in the fetus. The present study was designed to test the hypothesis that selective inhibition of PGHS-2 also inhibits the HPA response to cerebral hypoperfusion. We studied 13 chronically catheterized fetal sheep (126-136 days gestation). Five fetal sheep were subjected to intracerebroventricular infusion of nimesulide (0.01 mg/day), a specific inhibitor of PGHS-2, and eight were treated with vehicle (DMSO in water) for 5 days. Each fetus was subjected to a 10-min period of brachiocephalic occlusion, which decreased carotid arterial pressure approximately 75% and reflexively increased fetal plasma concentrations of ACTH, POMC, cortisol, and femoral arterial pressure, and decreased fetal heart rate. Nimesulide significantly inhibited the ACTH response to the BCO, while significantly augmenting the reflex cardiovascular response and altering fetal heart rate variability consistent with increased sympathetic nervous system activity. The results of this study demonstrate that the activity of PGHS-2 in the brain is a necessary component of the fetal HPA response to cerebral hypoperfusion in the late-gestation fetal sheep. These results are consistent with those of recent study, in which we demonstrated that the preparturient increase in fetal ACTH secretion depends upon PGHS-2 activity within the fetal brain.

Reproductive emergencies in camelids

Emergencies in theriogenology practice go beyond just saving the life of the patient, but also preserving its reproductive abilities. Camelid emergency medicine is a relatively new field. This paper discusses the most common reproductive emergencies, their diagnosis, treatment, and prognosis in male and female camelids. The conclusions drawn are based primarily on clinical observations by the authors over the last 25 years. Special consideration is given to peculiarities of the species, particularly in the choice of obstetrical manipulations and therapies.

Inhibition of brain prostaglandin endoperoxide synthase-2 prevents the preparturient increase in fetal adrenocorticotropin secretion in the sheep fetus

Maturation of the fetal hypothalamus-pituitary-adrenal axis is critical for the timely somatic development of the fetus and readiness for birth. Recently, we proposed that prostaglandin generation within the fetal central nervous system is critical for the modulation of hypotension-induced fetal ACTH secretion. The present study was designed to test the hypothesis that the preparturient increase in fetal ACTH secretion is dependent upon fetal central nervous system prostaglandin synthesis mediated by the activity of prostaglandin endoperoxide synthase (PGHS)-2 (cyclooxygenase-2) in the fetal brain. We performed two studies in chronically catheterized fetal sheep. In the first study, we infused nimesulide or vehicle intracerebroventricularly (i.c.v) into singleton fetal sheep and collected blood samples until spontaneous parturition. Nimesulide significantly delayed parturition, and inhibited fetal ACTH and proopiomelanocortin secretion but did not prevent the preparturient increase in fetal plasma cortisol concentration. In the second study, we used twin fetuses. One fetus received intracerebroventricular nimesulide and the other intracerebroventricular vehicle. Nimesulide reduced brain tissue concentrations of prostaglandin estradiol, while not affecting plasma prostaglandin E(2) concentrations, demonstrating an action restricted to the fetal brain. Nimesulide reduced PGHS-2 mRNA and increased PGHS-2 protein, while not altering PGHS-1 mRNA or protein in most brain regions, suggesting an effect of the inhibitor on PGHS-2 turnover and relative specificity for PGHS-2 in vivo. We conclude that the preparturient increase in fetal ACTH and proopiomelanocortin is dependent upon the activity of PGHS-2 in the fetal brain. However, we also conclude that the timing of parturition is not solely dependent upon ACTH in this species.