Chronic stress induces the expression of inducible nitric oxide synthase in rat brain cortex

Long-term exposure to stress has detrimental effects on several brain functions in many species, including humans, and leads to neurodegenerative changes. However, the underlying neural mechanisms by which stress causes neurodegeneration are still unknown. We have investigated the role of endogenously released nitric oxide (NO) in this phenomenon and the possible induction of the inducible NO synthase (iNOS) isoform. In adult male rats, stress (immobilization for 6 h during 21 days) increases the activity of a calcium-independent NO synthase and induces the expression of iNOS in cortical neurons as seen by immunohistochemical and western blot analysis. Three weeks of repeated immobilization increases immunoreactivity for nitrotyrosine, a nitration product of peroxynitrite. Repeated stress causes accumulation of the NO metabolites NO2+ NO3- (NOx-) accumulation in cortex, and these changes occur in parallel with lactate dehydrogenase (LDH) release and impairment of glutamate uptake in synaptosomes. Administration of the selective iNOS inhibitor aminoguanidine (400 mg/kg i.p. daily from days 7 to 21 of stress) prevents NOx- accumulation in cortex, LDH release, and impairment of glutamate uptake in synaptosomes. Taken together, these findings indicate that a sustained overproduction of NO via iNOS expression may be responsible, at least in part, for some of the neurodegenerative changes caused by stress and support a possible neuroprotective role for specific iNOS inhibitors in this situation.

Up-regulation of neuronal NO synthase immunoreactivity in opiate dependence and withdrawal

RATIONALE

Nitric oxide (NO) has been postulated to contribute significantly to analgesic effects of opiates as well as to the development of tolerance and physical dependence to morphine.

OBJECTIVE

The present study was undertaken to determine the effect of chronic morphine treatment and abstinence on the expression of neuronal NO synthase (neuronal NOS, nNOS) in several brain regions of mice.

METHODS

Seven days after the implantation of a 75 mg morphine pellet, adult male CD1 mice received a SC dose of 1 mg/kg naloxone. Fifteen minutes after the naloxone injection, brains were removed and nNOS expression was studied by using immunohistochemical methods.

RESULTS

Morphine-dependence produced an increase in the number of nNOS-positive cells in the main and accessory olfactory bulb, olfactory nuclei, cerebellum, locus coeruleus, medulla oblongata (nucleus of the solitary tract and prepositus hypoglossal nucleus), and a decrease in nNOS immunoreactivity in hypothalamus. The administration of naloxone to morphine-dependent mice to induce abstinence increased nNOS immunoreactivity in the hypothalamus and locus coeruleus.

CONCLUSIONS

These results indicate that the chronic treatment with morphine leads to alterations in nNOS expression in important regions implicated in the physical tolerance and dependence to opiates and suggest the use of specific inhibitors of this isoform in these conditions.

The human CILP gene: exon/intron organization and chromosomal mapping

The human cDNA for cartilage intermediate layer protein (CILP) codes for a larger precursor protein that consists of CILP and a homologue to porcine Nucleotide pyrophosphohydrolase (NTPPHase) [Lorenzo et al. 1998a. J. Biol. Chem. 273, 23469-23475]. The human gene has now been isolated and characterized. Southern blot analysis indicated a single copy of the CILP gene in the human genome. The gene spans approximately 15.3 kbp of genomic DNA, and is organized in nine exons. The 5' flanking region contains a putative promoter region with a TATA-like box localized from -29 to -23 bp upstream of the transcription start site. Analysis of the putative promoter region revealed potentially cis-regulatory eukaryotic elements such as GATA-1, MyoD, MZF1, and CdxA. The protein coding region begins in exon 2 with the putative signal peptide. CILP is encoded from exon 3 to exon 9. In addition, exon 9 also codes for the entire NTPPHase homologue and contains the 3' untranslated region of the gene. All the introns follow the 'gt-ag' rule, except the last intron, intron 8, that belongs to the minor class of pre-mRNA introns that contain 'at-ac' at their 5' and 3' ends, respectively. The CILP gene was mapped to human chromosome 15q22.

Neuroprotective effects of DETA-NONOate, a nitric oxide donor, on hydrogen peroxide-induced neurotoxicity in cortical neurones

Nitric oxide (NO) has been proposed to exert neuroprotective actions against oxidative damage acting directly as an antioxidant; in addition, it has also been suggested that NO might be cytoprotective by increasing cyclic GMP concentrations via activation of soluble guanylate cyclase. In this context, we have previously shown that cyclic GMP elevations confer cytoprotection against the neurotoxicity induced by SIN-1 in the presence of superoxide dismutase, conditions in which cell death seems to be a consequence of hydrogen peroxide (H2O2) formation. We have now found that H2O2 (20-100 microM) causes neurotoxicity in 1-week-old rat cortical neurones and that this effect is inhibited by the NO donor DETA-NONOate (1-10 microM). We have also found that 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylate cyclase, reverses the effect induced by DETA-NONOate, and that this action of ODQ is mimicked by 8-(4-chlorophenylthio)guanosine-3',5'-monophosphorothioate (Rp-8-pCPT-cGMPS), an inhibitor of cyclic GMP-dependent protein kinase, suggesting that the pathway affording protection involves activation of this kinase by cyclic GMP elevations. Simultaneously, ODQ inhibits the elevation of cyclic GMP concentrations induced by DETA-NONOate (1-3 microM) in cortical cells. Finally, we have also shown that the cyclic GMP mimetic, 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cyclic GMP) inhibits the neurotoxicity induced by H2O2 (30-40 microM). Taken together, these data demonstrate that NO-induced cyclic GMP elevations confer cytoprotection against H2O2-induced neuronal cell death.

Use of brain slices in the study of pathogenic role of inducible nitric oxide synthase in cerebral ischemia-reperfusion

We have recently demonstrated that inducible nitric oxide synthase (iNOS) is expressed in rat forebrain slices exposed to oxygen and glucose deprivation (OGD). Now, we have found that the expression of iNOS after OGD is time-dependent since 20 min of OGD produces the appearance of iNOS at earlier times than 10 min of OGD. OGD also causes neurotoxicity in this model, as revealed by the increase in excitatory amino acid, neuron specific enolase and lactate dehydrogenase (LDH) efflux to the incubation solution. Finally, the administration of the NMDA receptor antagonist MK-801 (100 nM) inhibits both the expression of iNOS and the release of LDH. Our findings demonstrate that this method may be considered an useful in vitro model of ischemia-reperfusion to determine the therapeutic role of neuroprotective tools.

Nitric oxide synthase activity in human squamous cell carcinoma of the head and neck

OBJECTIVES

To test whether nitric oxide synthase (NOS) is expressed in primary otolaryngologic tumors and whether this expression is associated with the degree of malignancy.

STUDY DESIGN

Twenty-six samples from the primary localization of human pharyngolaryngeal squamous cell carcinoma.

MATERIALS AND METHODS

the activity of calcium-dependent and calcium-independent NOS was analyzed by the conversion of L-[14C]-arginine into L-[14C]-citrulline.

RESULTS

NOS activity is below detectable levels in pharyngolaryngeal mucosa from noncancer patients. In the primary localization of the tumor, calcium-independent NOS activity is maximal at early stages of tumor growth, whereas calcium-dependent activity increases from early to advanced stages.

CONCLUSIONS

These data suggest that tumor growth and malignancy is associated with a change in the enzymatic source of NO from calcium-independent NOS to calcium-dependent NOS isoform in primary localization. These data suggest that the inhibition of calcium-independent NOS activity in early stages and/or inhibition of calcium-dependent NOS activity in later stages could delay growth of solid tumors.

Down-regulation of neuronal nitric oxide synthase by nitric oxide after oxygen-glucose deprivation in rat forebrain slices

The precise role that nitric oxide (NO) plays in the mechanisms of ischemic brain damage remains to be established. The expression of the inducible isoform (iNOS) of NO synthase (NOS) has been demonstrated not only in blood and glial cells using in vivo models of brain ischemia-reperfusion but also in neurons in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). We have used this experimental model to study the effect of OGD on the neuronal isoform of NOS (nNOS) and iNOS. In OGD-exposed rat forebrain slices, a decrease in the calcium-dependent NOS activity was found 180 min after the OGD period, which was parallel to the increase during this period in calcium-independent NOS activity. Both dexamethasone and cycloheximide, which completely inhibited the induction of the calcium-independent NOS activity, caused a 40-70% recovery in calcium-dependent NOS activity when compared with slices collected immediately after OGD. The NO scavenger oxyhemoglobin produced complete recovery of calcium-dependent NOS activity, suggesting that NO formed after OGD is responsible for this down-regulation. Consistently, exposure to the NO donor (Z)-1-[(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-iu m-1,2-diolate (DETA-NONOate) for 180 min caused a decrease in the calcium-dependent NOS activity present in control rat forebrain slices. Furthermore, OGD and DETA-NONOate caused a decrease in level of both nNOS mRNA and protein. In summary, our results indicate that iNOS expression down-regulates nNOS activity in rat brain slices exposed to OGD. These studies suggest important and complex interactions between NOS isoforms, the elucidation of which may provide further insights into the physiological and pathophysiological events that occur during and after cerebral ischemia.

Cloning and deduced amino acid sequence of a novel cartilage protein (CILP) identifies a proform including a nucleotide pyrophosphohydrolase

The cDNA cloning and expression in vitro and in eukaryotic cells of a novel protein isolated from human articular cartilage, cartilage intermediate layer protein (CILP) is described. A single 4. 2-kilobase mRNA detected in human articular cartilage encodes a polypeptide of 1184 amino acids with a calculated molecular mass of 132.5 kDa. The protein has a putative signal peptide of 21 amino acids, and is a proform of two polypeptides. The amino-terminal half corresponds to CILP (molecular mass of 78.5 kDa, not including post-translational modifications) and the carboxyl-terminal half corresponds to a protein homologous to a porcine nucleotide pyrophosphohydrolase, NTPPHase (molecular mass of 51.8 kDa, not including post-translational modifications). CILP has 30 cysteines and six putative N-glycosylation sites. The human homolog of porcine NTPPHase described here contains 10 cysteine residues and two putative N-glycosylation sites. In the precursor protein the NTPPHase region is immediately preceded by a tetrapeptide conforming to a furin proteinase cleavage consensus sequence. Expression of the full-length cDNA in a cell-free translation system and in COS-7 or EBNA cells indicates that the precursor protein is synthesized as a single polypeptide chain that is processed, possibly by a furin-like protease, into two polypeptides upon or preceding secretion.

A novel cartilage protein (CILP) present in the mid-zone of human articular cartilage increases with age

A novel, somewhat basic noncollagenous protein was purified from guanidine hydrochloride extracts of human articular cartilage using cesium chloride density gradient centrifugation, followed by ion-exchange chromatography at pH 5, and gel filtration on two serially coupled columns of Superose 6 and Superdex 200. The protein of 91.5 kDa contains a single polypeptide chain substituted with N-linked oligosaccharides. It appeared unique to cartilage as studied by enzyme-linked immunosorbent assay and immunoblots of various tissue extracts. Its concentration in articular cartilages showed some variability with age being lower in young individuals. It represents a chondrocyte product, since it is synthesized by articular chondrocytes in explant cultures. Interestingly, the distribution of the protein in the articular cartilage provides important information on the nature of chondrocytes at different compartments in the tissue. Thus, chondrocytes in the middle/deeper layers of the tissue in particular, appeared to have produced the protein and deposited it in the interterritorial matrix. The protein was neither seen in the superficial nor in the deepest regions of the articular cartilage. Based on its immunolocalization we have named this protein CILP (cartilage intermediate layer protein).

Protective effect of N-(3-(aminomethyl)benzyl) acetamidine, an inducible nitric oxide synthase inhibitor, in brain slices exposed to oxygen-glucose deprivation

It has been suggested that large amounts of nitric oxide (NO) produced by inducible NO synthase are involved in the mechanisms of neurotoxicity after cerebral ischaemia. We have recently demonstrated that inducible NO synthase was expressed within hours after rat forebrain slices were exposed to oxygen-glucose deprivation. Therefore, we sought to determine whether NO produced by inducible NO synthase contributes to tissue damage in this model, by using a new, highly selective, inhibitor of inducible NO synthase, N-(3-(aminomethyl)benzyl)acetamidine (1400W). We found that incubation with 1400W from the start of the oxygen-glucose deprivation period until the end of the experiment decreases tissue damage determined as lactate dehydrogenase (LDH) efflux 4 h after the oxygen-glucose deprivation period, the time at which inducible NO synthase expression is maximal in this model. This effect may be a result of direct inhibition of inducible NO synthase activity, raising the possibility of a clinical use of selective inhibitors of this NO synthase isoform in the management of cerebral ischaemia.

Neuronal death induced by SIN-1 in the presence of superoxide dismutase: protection by cyclic GMP

The nitrovasodilator 3-morpholinosydnonimine (SIN-1) slowly decomposes to release both nitric oxide (NO) and superoxide (O2-) and thereby produces peroxynitrite (ONOO-), a powerful oxidant which has been proposed to mediate the toxic actions caused by NO. Indeed, ONOO has been shown to cause neuronal death and it has been proposed to occur in different disorders of the CNS such as brain ischaemia, AIDS-associated dementia, amyothrophic lateral sclerosis, etc. We have found that SIN-1 was only slightly toxic to 1-week-old rat cortical neurones in primary culture (LC50=2.5+/-0.5 mM). Superoxide dismutase (SOD; 100 U/ml) significantly increased SIN-1-induced toxicity, an effect that was enhanced in the presence of HbO2, abolished by catalase and accompanied by the formation of hydrogen peroxide (H2O2). We have also found that 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylate cyclase, enhances cell death induced by SIN-1 (0.2-0.5 mM) + SOD (100 U/ml) in a concentration-dependent way (EC50=0.073+/-0.004 microM). Simultaneously, ODQ inhibits the elevation of cyclic GMP concentrations induced by SIN-1 + SOD in cortical cells (IC50=0.022+/-0.014 microM). Finally, we have also shown that the cyclic GMP mimetic, 8-bromo-cyclic GMP reverses the potentiating effect induced by ODQ on SIN-1 + SOD-induced neuronal death and inhibits the neurotoxicity induced by H2O2 (100 microM). Taken together, these data suggest that H2O2 is the species responsible for the potentiation by SOD of SIN-1-induced cell death and that cyclic GMP elevations confer selective cytoprotection against this H2O2-mediated component of cell death.

Peroxynitrite causes aspartate release from dissociated rat cerebellar granule neurones

Peroxynitrite (ONOO-) is a powerful oxidant which is formed from the reaction between nitric oxide (NO) and superoxide anion. It has therefore been proposed to mediate the toxic actions caused by NO. Since ONOO- may be formed in the central nervous system (CNS) in pathological conditions such as brain ischaemia, we decided to investigate whether this molecule induces the release of the endogenous excitatory amino acids glutamate and aspartate from neurones. We selected as biological model acutely dissociated rat cerebellar granule neurones in suspension to allow a direct interaction between ONOO- and target cells. Peroxynitrite caused a concentration-dependent release of aspartate but not of glutamate from dissociated cerebellar granule neurones. Peroxynitrite-induced aspartate release was inhibited by dithiothreitol, tetrodotoxin, and in Na+-deprived solutions and not affected by EGTA or pre-incubation with the cytosolic Ca2+ chelator BAPTA/AM. Peroxynitrite also induced an increase in intracellular Ca2+ concentration which was not affected in the presence of EGTA. These data show that ONOO- causes release of aspartate from cerebellar granule neurones and that this effect might arise from an alteration of Na+ membrane permeability leading subsequently to reversal of a Na+-dependent plasma membrane transporter of this excitatory amino acid. In addition, ONOO- alters Ca2+ homeostasis likely due to Na+ overload. Taken together, these findings may help and elucidate some of the intimate mechanisms of NO-induced neuronal damage in pathological circumstances.

Neuronal expression of inducible nitric oxide synthase after oxygen and glucose deprivation in rat forebrain slices

Nitric oxide (NO) overproduction has been postulated to contribute significantly to ischaemia-reperfusion neurotoxicity. Inducible or type II NO synthase (iNOS) synthesizes NO in large quantities for long periods of time. Therefore we investigated the expression and localization of iNOS after oxygen and glucose deprivation in rat forebrain slices. In this experimental model, calcium-independent NOS activity reached a maximum 180 min after the end of a 20 min oxygen-glucose deprivation period. During the same period of time, the calcium-independent activity was absent in control forebrain slices. To test whether this calcium-independent NOS activity was due to the expression of iNOS, the effects of the addition of dexamethasone, cycloheximide and pyrrolidine dithiocarbamate were determined. All of them inhibited the induction of the calcium-independent NOS activity measured in the rat forebrain slices after oxygen and glucose deprivation. Furthermore, oxygen and glucose deprivation caused the expression of the gene encoding iNOS in rat forebrain slices, as assessed by the detection of iNOS message and protein in these samples. A sixfold increase in the iNOS mRNA levels was observed at 180 min and the time-course of the expression of iNOS mRNA was in agreement with the temporal profile of iNOS enzymatic activity. Immunohistochemistry analysis revealed that iNOS was highly expressed in neurones, astrocytes and microglial cells. These results demonstrate for the first time that iNOS is expressed in neurones after oxygen and glucose deprivation, and that this expression occurs in short periods of time. These findings suggest that NO can play an important pathogenic role in the tissue damage that occurs after cerebral ischaemia.

Inhibition of morphine withdrawal by lamotrigine: involvement of nitric oxide

We studied the effects of lamotrigine [3,5-diamino-6-(2,3-dichlorophenyl)- 1,2,4-triazine], a new antiepileptic compound, on naloxone-precipitated morphine withdrawal in mice. Pretreatment with lamotrigine (5-100 mg/kg, s.c.) reversed in a dose-dependent way the withdrawal-induced increase in cerebellar Ca(2+)-dependent nitric oxide (NO) synthase activity and reduced the number of escape jumps and other motor symptoms of abstinence, at doses that did not modify locomotor activity (25-50 mg/kg). Pretreatment with the NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydroxy-5H- dibenzo[a,d]cyclohepten-5,10-imine; dizocilpine] (0.1-0.3 mg/kg, s.c.) also reversed the increase in cerebellar Ca(2+)-dependent NO synthase activity. However, although MK-801 reduced the number of escape jumps and other motor symptoms of abstinence, its effects were not clearly dose-dependent. Furthermore, the highest dose of MK-801 tested (0.3 mg/kg) caused an impairment of the locomotor behaviour in naive mice. Thus, lamotrigine may represent a new and useful agent for the treatment of opiate abstinence.

Effects of trepelennamine on brain monoamine turnover in morphine dependent and abstinent mice

Previous studies have reported that the histamine H1 receptor blocker tripelennamine potentiates morphine withdrawal. In this paper, the in vivo effects produced by tripelennamine on the turnover of serotonin (5-HT), dopamine (DA) and noradrenaline (NA) in the whole brain, excluding the cerebellum, were studied in control, morphine-dependent (by SC implantation of a 75 mg morphine pellet) and morphine-dependent male CD1 mice just before naloxone-precipitated withdrawal. Tripelennamine (1-10 mg/kg) was administered SC 45 min. before the animals were killed. Serotonin, 5-hydroxyindole-3-acetic acid (5-HIAA), dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and noradrenaline were measured by high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) was measured by HPLC coupled with fluorimetric detection. Ratios 5-HIAA/ 5-HT, DOPAC + HVA/DA and MHPG/NA were taken as an index of serotonin, dopamine and noradrenaline turnovers, respectively. Tripelennamine (1 and 10 mg/kg) significantly reduced serotonin turnover in control and morphine-dependent mice, and potentiated the serotonin turnover reduction when it was administered 30 min before naloxone injection. The dopamine turnover was diminished by tripelennamine (1 and 10 mg/kg) in the morphine-dependent group. Tripelennamine (10 mg/kg) reduced noradrenaline turnover during abstinence. These results suggest that the potentiation of opiate abstinence by tripelennamine could be related to its antiserotonergic profile.

Correlation between brain nitric oxide synthase activity and opiate withdrawal

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.

Morphine-induced changes in cerebral and cerebellar nitric oxide synthase activity

The effect of acute and chronic morphine treatment on nitric oxide (NO) synthase activity (determined by the rate of conversion of [14C]arginine into [14C]citrulline) on mouse brain was studied. Acute morphine treatment induced an increased in Ca2+ -dependent NO synthase in cerebellum. This effect was blocked by coadministration with naloxone. Chronic morphine treatment (by s.c. pellet) also produced an increase in cerebellar NO synthase, with a maximum on the second day of implantation. No significant changes were found in frontal cortex and forebrain during acute or chronic morphine treatment. The relationship between opiate effects and the L-arginine: NO pathway is discussed.

[Chronological aspects of the nuclear maturation of bovine oocytes cultivated in vitro]

In this study, the chronological changes in the meiotic progress of in vitro maturation of bovine oocytes was analysed. Oocytes (n = 1044) were obtained from a local abattoir and were classified into two groups according to the presence or absence of cumulus cells. They were incubated in microdrops (5 per drop) in TCM-199 (control), TCM-199 + 10% fetal calf serum (treatment 2) and TCM-199 + 10% estrous cow serum (treatment 3). Oocytes were fixed and stained at the end of 0, 6, 12, 18, 24 and 30 h of the beginning of in vitro culture, were evaluated according to the nuclear stage of maturation. These results demonstrated that the immature oocytes at the time of collection (0 h) were in the germinal vesicle stage (GV), and that the highest maturation rate was at 24 h of culture in all treatments. Serum treatments enhanced the maturation rates obtained (52.1 and 55.7%) compared to control (serum-free) medium (42.7%; P < 0.05) in cumulus-cell-enclosed oocytes. In denuded oocytes, the maturation rates were lower compared to cumulus-cells-enclosed oocytes in all treatments. In conclusion, meiotic progression of bovine oocytes can be influenced by the inclusion of sera in the maturation media and by the presence of the cumulus cells.

Changes induced by sodium cromoglycate in brain catecholamine turnover in morphine dependent and abstinent mice

The effects of sodium cromoglycate (CRO) were studied in relation to the metabolism of brain catecholamines: dopamine (DA) and noradrenaline (NA), and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG). CRO was injected SC in control mice, morphine-tolerant mice (tolerance was induced by SC implantation of a 75 mg morphine pellet; CRO was administered on day 4 of addiction) and 30 min before abstinence (withdrawal was induced by SC injection of naloxone (1 mg/kg) on day 4 of addiction). Brain catecholamines and their metabolites were measured using high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD), for DA, NA, DOPAC and HVA, and coupled with fluorescence detection for MHPG. The ratios of DOPAC + HVA/DA and MHPG/NA were kept as an index of DA and NA turnovers, respectively. CRO administered 30 min before naloxone-precipitated withdrawal diminished significantly NA levels in frontal cortex. CRO increased DA turnover in striatum and frontal cortex in naive animals and significantly diminished DA levels in frontal cortex and DOPAC levels in frontal cortex and midbrain in morphine-dependent mice. These findings are discussed in relation to the protective effects of CRO on opiate withdrawal and the effects of CRO on locomotor activity.

[Specific actions of growth factors (EGF and IGF-I) on the in vitro maturation of bovine oocytes]

Growth factors (EGF and IGF-I) have different actions on mammalian cells such as proliferation and differentiation. The effect of EGF and IGF-I was examined on in vitro matured bovine oocytes. Immature oocytes were obtained by follicular aspiration from slaughtered heifer ovaries and classified in two groups, with or without cumulus cells. Oocytes (n = 1,037) were cultured in a serum-free media (TCM-199) for 24 hours at 39 degrees C in absence of hormones and were divided in 5 treatments: control, EGF (20 ng/ml and 50 ng/ml), IGF-I (100 ng/ml) and EGF + IGF-I (50 ng/ml + 100 ng/ml). Results suggest that the EGF + IGF-I treatment increases significantly (p < 0.01) the maturation rate (60.3%) as compared to control medium (36.5%) in cumulus cell-enclosed oocytes. No significant differences were observed between the treatments in the denuded oocytes. The effect of EGF + IGF-I added to the maturation media seems to be mediated by the surrounding cumulus cells and enhanced the in vitro maturation rate on cumulus cell-enclosed bovine oocytes.