雷洛昔酚对大鼠垂体的作用

目的 观察雷洛昔酚是否能诱发出催乳素瘤的动物模型以及对PRL水平的影响,以研究雷洛昔酚对大鼠垂体的作用.方法 雌性Wistar大鼠切除卵巢后,分别在皮下埋植含有雷洛昔酚、雌激素和空白硅胶管,术后8周处死大鼠,检测大鼠体重变化、垂体重量变化、血清催乳素(PRL)水平和垂体组织学变化.结果 雷洛昔酚组与阴性对照组大鼠体重无明显统计学差异,与雌激素组大鼠体重具有统计学差异(P＜0.05);雷洛昔酚组与阴性对照组大鼠垂体重相比无明显差异,与雌激素组大鼠垂体重相比具有统计学差异(P＜0.05);雌激素组大鼠血清PRL水平最高,阴性对照组血清PRL水平最低,雷洛昔酚组介于两者之间,分别与雌激素组、对照组相比较差异均具有统计学意义(P＜0.05);雷洛昔酚组与对照组垂体病理为正常细胞形态,雌激素组垂体病理为PRL瘤表现.结论 雷洛昔酚对大鼠垂体有一定的影响,但不能诱发催乳素瘤.     

Immunoreactive tyrosine hydroxylase in the brain and pituitary gland of the platyfish

Immunoreactive tyrosine hydroxylase (ir-TH), the rate-limiting enzyme for the synthesis of dopamine and other catecholamines, was localized in the brain and pituitary gland of sexually mature platyfish (Xiphophorus maculatus). This is the first report of ir-TH in the nucleus olfactoretinalis, an LHRH-containing nucleus in the brain which plays an important role in the development and functioning of the reproductive system in platyfish. Ir-TH was also localized in the nucleus preopticus and paraventricular organ. In the pituitary gland ir-TH is found in the prolactin cells and in some fish, in some of the gonadotropin-containing cells of the pars intermedia, but not in the gonadotrops of the pars distalis. The localization of ir-TH in brain centers and pituitary cells associated with reproductive system regulation is discussed in the context of the interaction of monamines, neuropeptides and pituitary hormones during the maturation and operation of the brain-pituitary-gonadal axis.     

Identification of endorphin acetyltransferase in rat brain and pituitary gland

An enzyme which N-acetylates beta-endorphin has been identified and characterized in the rat brain and pituitary gland. The beta-endorphin acetyltransferase activity was localized almost exclusively in the intermediate lobe of the pituitary gland. beta-endorphin acetyltransferase activity was also present in the hypothalamus, a brain region which synthesizes beta-endorphin, but not the cerebellum, a region which does not synthesize beta-endorphin. The substrate specificity of beta-endorphin acetyltransferase appeared to be located in the NH2 terminus and midportions of the beta-endorphin sequence. The regional distribution and pharmacological specificity of beta-endorphin acetyltransferase indicate that it is a highly specialized regulatory enzyme. Because N-acetyl-beta-endorphin is nonanalgesic and does not bind to the opiate receptor (Smyth, D.G., Massey, D.E., Zakarian, S., and Finnie, M.D. (1979) Nature (Lond.) 279, 252-254), it appears that the physiological significance of beta-endorphin acetyltransferase is that it can modulate the activity of endorphin secreted from opiomelanotropinergic cells and neurons.     

Telomeric expression sites are highly conserved in Trypanosoma brucei

Subtelomeric regions are often under-represented in genome sequences of eukaryotes. One of the best known examples of the use of telomere proximity for adaptive purposes are the bloodstream expression sites (BESs) of the African trypanosome Trypanosoma brucei. To enhance our understanding of BES structure and function in host adaptation and immune evasion, the BES repertoire from the Lister 427 strain of T. brucei were independently tagged and sequenced. BESs are polymorphic in size and structure but reveal a surprisingly conserved architecture in the context of extensive recombination. Very small BESs do exist and many functioning BESs do not contain the full complement of expression site associated genes (ESAGs). The consequences of duplicated or missing ESAGs, including ESAG9, a newly named ESAG12, and additional variant surface glycoprotein genes (VSGs) were evaluated by functional assays after BESs were tagged with a drug-resistance gene. Phylogenetic analysis of constituent ESAG families suggests that BESs are sequence mosaics and that extensive recombination has shaped the evolution of the BES repertoire. This work opens important perspectives in understanding the molecular mechanisms of antigenic variation, a widely used strategy for immune evasion in pathogens, and telomere biology.     

Abundance of endothelin-3 in rat intestine, pituitary gland and brain

We established a highly sensitive and specific sandwich-enzyme immunoassay (EIA) for endothelin-3 (ET-3), which showed no crossreactivity with endothelin-1 (ET-1), endothelin-2 (ET-2) and big-endothelin-1 (big-ET-1). We had previously established a sensitive sandwich-EIA for ET-1, which fully crossreacted with ET-2, but not with ET-3 or big-ET-1. These EIAs were used to examine the tissue distribution of immunoreactive (ir-) ET-3 and compare them with those of ir-ET-1 (including ir-ET-2) in Sprague-Dawley rats. High concentrations of ir-ET-3 were found in the intestine, lung, pituitary gland and brain (greater than 100 pg/g wet tissue), ir-ET-1(ET-2) showed widespread distribution, with large amounts in the lung and colon (greater than 1000 pg/g wet tissue). The pituitary gland was the only organ containing higher amounts of ir-ET-3 than ir-ET-1 (ET-2). In reverse phase-high performance liquid chromatography coupled with EIAs, the ir-ET-3 was exclusively eluted at the position of synthetic ET-3, indicating that the ir-ET-3 was identical to ET-3. The abundance of ET-3 in the intestine, pituitary gland and brain indicates that ET-3 is a new brain-gut peptide which may have a physiological function in nervous and endocrine systems.     

Retrospective data on the pituitary gland response during immune and neoplastic processes

A synthesis of many experimental works performed during the last ten years regarding the nonspecific response of the pituitary gland during some immune and neoplastic processes is presented. Different modalities of the response of pituitary gland cell that vary depending on the antigen type were observed. The TAB vaccine inducing a humoral immune response determined an increased secretory activity of STH and FSH cells which are involved by their secretions in the activation of protein synthesis also including antibodies. The tumoral antigens also representing a stressing factor brought about a more intense activity besides the FSH cells, the ACTH and TSH cells.     

Identification,expression, and characterization of the highly conserved D-xylose isomerase in animals

D-xylose is a necessary sugar for animals. The xylanase from a mollusk, Ampullaria crossean, was previously reported by our laboratory. This xylanase can degrade the xylan into D-xylose. But there is still a gap in our knowledge on its metabolic pathway. The question is how does the xylose enter the pentose pathway？ With the help of genomic databases and bioinformatic tools, we found that some animals, such as bacteria, have a highly conserved D-xylose isomerase （EC 5.3.1.5）. The xyiose isomerase from a sea squirt, Ciona intestinali, was heterogeneously expressed in Escherichia coli and purified to confirm its function. The recombinant enzyme had good thermal stability in the presence of Mg^2＋. At the optimum temperature and optimum pH environment, its specific activity on D-xylose was 0.331 μmol/mg/min. This enzyme exists broadly in many animals, but it disappeared in the genome of Amphibia-like Xenopus laevis. Its sequence was highly conserved. The xylose isomerases from animals are very interesting proteins for the study of evolution.     

Electron-microscopic study on the anterior pituitary gland of spontaneous dwarf rats

Summary The spontaneous dwarf rat is a novel experimental model animal on the study of pituitary dwarfism. The fine structure of the anterior pituitary cells was studied in the immature and mature dwarf rats. Pituitary glands were removed from 5-, 10-, 20-day-old immature dwarfs, adult (45 days-16 weeks) dwarfs and normal 3-month-old rats and processed for electron-microscopic observation. In the control animals, growth hormone cells were readily identified by their ultrastructural characteristics, such as the presence of numerous electron-dense secretory granules, 300–350 nm in diameter, well developed rough endoplasmic reticulum and a prominent Golgi complex. In contrast, growth hormone cells were not found in the anterior pituitary gland of the spontaneous dwarf rat at any age examined. Other pituitary cell types, i.e., luteinizing hormone/ follicle stimulating hormone, thyroid stimulating hormone, adrenocorticotropic hormone and prolactin cells, appeared similar in their fine structure to those found in the control rats. In the pituitary gland of dwarf rats, a number of polygonal cells were observed either with no or relatively few secretory granules. The rough endoplasmic reticulum was arranged in parallel cisternae and the Golgi complex was generally prominent in these cells. In addition, many were found to have abundant lysosomes. A few minute secretory granules were occasionally observed; however, the immunogold technique failed to localize growth hormone or prolactin in the granules. The nature of these cells remained obscure in this study. Since their incidence and fine structural features, other than the secretory granules, were quite similar to those of the growth hormone cells in normal rats, we postulate that these cells are dysfunctional growth hormone cells. These results suggest that the cause of the growth impairment in the spontaneous dwarf rat is due to a defect in the functional growth hormone cells in the pituitary gland, and since other pituitary cell types appeared normal, the disorder seems to be analogous to the isolated growth hormone deficiency in the human.     

Ept7 influences estrogen action in the pituitary gland and body weight of rats

Estrogens control many aspects of pituitary gland biology, including regulation of lactotroph homeostasis and synthesis and secretion of prolactin. In rat models, these actions are strain specific and heritable, and multiple quantitative trait loci (QTL) have been mapped that impact the responsiveness of the lactotroph to estrogens. One such QTL, Ept7, was mapped to RNO7 in female progeny generated in an intercross between BN rats, in which the lactotroph population is insensitive to estrogens, and ACI rats, which develop lactotroph hyperplasia/adenoma and associated hyperprolactinemia in response to estrogen treatment. The primary objective of this study was to confirm the existence of Ept7 and to quantify the impact of this QTL on responsiveness of the pituitary gland of female and male rats to 17β-estradiol (E2) and diethylstilbestrol (DES), respectively. Secondary objectives were to determine if Ept7 influences the responsiveness of the male reproductive tract to DES and to identify other discernible phenotypes influenced by Ept7. To achieve these objectives, a congenic rat strain that harbors BN alleles across the Ept7 interval on the genetic background of the ACI strain was generated and characterized to define the effect of administered estrogens on the anterior pituitary gland and male reproductive tissues. Data presented herein indicate Ept7 exerts a marked effect on development of lactotroph hyperplasia in response to estrogen treatment, but does not affect atrophy of the male reproductive tissues in response to hormone treatment. Ept7 was also observed to exert gender specific effects on body weight in young adult rats.     

Distribution of methionine- and leucine-enkephalin within the rat pituitary gland measured by highly specific radioimmunoassays

The distribution of methionine- and leucine-enkephalin within the rat pituitary gland was measured using highly specific antisera in conjunction with purification by high performance liquid chromatography. The highest concentrations were found in the pars intermedia (7 pmole/mg for methionine-enkephalin, 4 pmole/mg for leucine-enkephalin), whilst the pars nervosa contained 2.2 pmole/mg of each and the pars anterior the least (methionine-enkephalin: 0.51 pmole/mg, leucine-enkephalin: 0.36 pmole/mg).     

Immunocytochemical localization of serotonin in the brain and pituitary gland of the platyfish,Xiphophorus maculatus

Summary Immunoreactive serotonin (ir-5HT) containing cells were localized in the brain and pituitary gland of the platyfish by use of immunoperoxidase procedures. In the brain, ir-neurons were found lining the wall of the third ventricle and in its lateral and posterior recesses. More caudally, ir-perikarya were found in the valvular portion of the cerebellum and in the raphe region. Ir-5HT was also localized within the pineal gland in fish that had been sacrificed before 1:00 p.m. Within the pituitary gland, ir-5HT was localized in periodic acid Schiff-positive cells of the pars intermedia of all fish while, in only a few animals, less intense immunoreactivity was also present in gonadotrops of the caudal pars distalis.     

Altered expression of neprilysin family members in the pituitary gland of sleep-disturbed rats, an animal model of severe fatigue

Alterations of the expression of some peptidases in the pituitary gland of a fatigued rat model were identified. Rats were kept in a cage filled with water to a height of 1.5 cm to disturb deep sleep. After 24-h sleep disturbance, expression of neutral endopeptidase 24.11 (neprilysin) mRNA was increased in the intermediate lobe of the pituitary gland, whereas the mRNA expression of another family member, damage-induced neuronal endopeptidase, which is normally expressed in a subgroup of anterior pituitary cells, was significantly suppressed. These alterations were demonstrated by RT-PCR, northern blotting and in situ hybridization. Other family members, such as neprilysin 2 and endothelin converting enzyme-1, did not show any change in mRNA expression. An increase of neprilysin mRNA expression was not seen in any other tissues of the sleep-disturbed rats. The enzymatic activity of neprilysin was also increased in the pituitary. The augmentation of neprilysin expression and activity was prolonged as long as the sleep disturbance continued (up to 5 days), and returned to the basal level when rats were allowed to sleep freely. These results suggest that peptide processing and degradation in the pituitary may be an influential factor in fatigued states such as sleep disturbance.     

Stress-induced testicular hyposensitivity to gonadotropin in rats. Role of the pituitary gland

The time course of stress-induced testicular hyposensitivity to gonadotropins was studied in hypophysectomized or naloxone-treated rats exposed to various periods of immobilization. Blood was collected from a chronically indwelling intra-atrial catheter every hour for luteinizing hormone (LH) and testosterone (T) measurement. Eight hours of immobilization completely suppressed T secretion without significant effect on LH. Human chorionic gonadotropin (hCG, 5 IU/rat, i.m.) induced a marked increase in plasma T levels in normal control groups 3 h post-injection while in immobilized rats the response was completely abolished, even after only 30 min of stress. In hypophysectomized rats, as expected, plasma T levels were undetectable, but, contrary to results obtained in normal animals, hCG induced a similar increase of plasma T levels both in control and stressed rats. Immobilization stress failed to inhibit plasma T values in hypophysectomized rats pretreated for 4 days with human menopausal gonadotropin (hMG) + hCG, while it did so in similarly treated normal animals. Naloxone induced a rise of plasma LH and T levels in control rats, but did not antagonize the stress-induced fall of plasma T concentration. In all groups, steroid testicular content mimicked variations of plasma T values. In particular, in stressed animals the lack of accumulation of testicular 17-hydroxyprogesterone probably reflected a normal activity of 17-20 lyase. These results indicate that stress induces very rapidly a state of Leydig cell hyposensitivity to gonadotropins and a blockade of T biosynthesis. The causal relationship between the two effects is presently not clear but these events seem to be due to stress-induced release of an inhibitory factor of pituitary origin other that endorphin.