Studies on the response of ewes to live chlamydiae adapted to chicken embryos or tissue culture. (1/6081)

Ewes infected before gestation with chicken embryo or tissue culture adapted chlamydial strain B-577 were challenge inoculated with the homologous strain at four to 18 weeks of gestation. The ewes responsed with group specific complement fixing antibody titers of 1:8 to 1:256 by the second week after initial infection. A secondary antibody response in the surviving challenge inoculated ewes occurred at the time of lambing and reached titers of 1:32 to 1:256 by the second week after parturition. Group specific complement fixing antibodies did not appear to play a significant role in resistance to chlamydial infection. Ewes infected with the chicken embryo adapted strain B-577 excreted chlamydiae in their feces 60 days after inoculation. However, chlamydiae were not recovered from feces of ewes infected with the tissue culture adapted strain B-577. Placentas of ewes challenge inoculated by the intravenous route were consistently infected. Chlamydiae were recovered from placentas, some fetuses and lambs. In two instances when challenge inoculation was given by the intramuscular route, infection was detected only by the direct fluorescent antibody method.  (+info)

In vitro development of sheep preantral follicles. (2/6081)

Preantral ovarian follicles isolated from prepubertal sheep ovaries were individually cultured for 6 days in the presence of increasing doses of FSH (ranging from 0.01 to 1 microg/ml) and under two different oxygen concentrations, 20% and 5% O2. Follicle development was evaluated on the basis of antral cavity formation as well as the presence of healthy cumulus oocyte complexes. Follicle growth was enhanced by FSH addition to culture medium, while the use of a low oxygen concentration slightly stimulated this process. However, when follicles were cultured in the presence of high doses of FSH (1 microgram/ml) and under low oxygen concentration, a high proportion of them showed the presence of an antral cavity and of a healthy cumulus-oocyte complex. In addition, under this specific culture condition sheep preantral follicles released higher levels of estradiol as compared to those secreted at lower FSH concentrations or under 20% O2. When the meiotic competence of oocytes derived from follicles cultured at 1 microgram/ml FSH was assessed, no significant difference was recorded between the two oxygen groups. These results show that the culture conditions here identified are beneficial to in vitro growth and differentiation of sheep preantral follicles.  (+info)

Ontogeny of expression of a receptor for platelet-activating factor in mouse preimplantation embryos and the effects of fertilization and culture in vitro on its expression. (3/6081)

Platelet-activating factor (PAF; 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent ether phospholipid. It is one of the preimplantation embryo's autocrine growth/survival factors. It may act via a G protein-linked receptor on the embryo; however, the evidence for this is conflicting. The recent description of the intracellular form of the PAF:acetlyhydrolase enzyme as having structural homology with G proteins and Ras also suggests this as a potential intracellular receptor/transducer for PAF. This study used reverse transcription-polymerase chain reaction to examine the ontogeny of expression of the genes for these proteins in the oocyte and preimplantation-stage embryo. Transcripts for the G protein-linked PAF receptor were detected in the late 2-cell-stage embryo and in all stages from the 4-cell stage to blastocysts. They were also present in unfertilized oocytes and newly fertilized zygotes but only at relatively low levels. The incidence of expression was generally low and variable in late zygotes and early 2-cell embryos. Expression past the 2-cell stage was alpha-amanitin sensitive. The results indicated that mRNA for this receptor is a maternal transcript that was degraded during the zygote-2-cell stage. New expression of the receptor transcript required activation of the zygotic genome. Fertilization of embryos in vitro caused this transcript not to be expressed in the zygote. Culture of zygotes (irrespective of their method of fertilization) caused expression from the zygotic genome to be retarded by more than 24 h. This retardation did not occur if culture commenced at the 2-cell stage. The transcripts for the subunits of intracellular PAF:acetylhydrolase were not detected in oocytes or at any stage of embryo development examined, despite their being readily detected in control tissue. This study confirms the presence of the G protein-linked PAF receptor in the 2-cell embryo and describes for the first time its normal pattern of expression during early development. The adverse effects of in vitro fertilization (IVF) and embryo culture on the expression of this transcript may be a contributing factor for the poor viability of embryos produced in this manner. The reduced expression of PAF-receptor mRNA following IVF predicts that such embryos may have a deficiency in autocrine stimulation and also suggests that supplementation of growth media with exogenous PAF would be only partially beneficial. The effect of IVF and culture may also explain the conflicting literature.  (+info)

Steroid regulation of retinol-binding protein in the ovine oviduct. (4/6081)

Two studies were conducted to identify retinol-binding protein (RBP) expression in the ovine oviduct and to determine the role of ovarian steroids in its regulation. Ewes were salpingectomized on Days 1, 5, or 10 of their respective estrous cycles, and oviducts were homogenized for RNA analysis, fixed for immunocytochemistry (ICC), or cultured for 24 h for protein analysis. ICC localized RBP to the epithelium of all oviducts. RBP synthesis was demonstrated by immunoprecipitation of radiolabeled RBP from the medium of oviductal explant cultures. Explant culture medium from oviducts harvested on Day 1 contained significantly more RBP than medium from oviducts collected on Days 5 or 10. Slot-blot analysis demonstrated that steady-state RBP mRNA levels were significantly higher on Day 1 than Day 5 or 10. In the second experiment, ovariectomized ewes were treated with estradiol-17beta (E2), progesterone (P4), E2+P4 (E2+P4), or vehicle control, and oviducts were analyzed as above. P4 alone or in combination with E2 significantly reduced steady-state RBP mRNA levels compared to those in E2-treated animals. Oviductal explants from E2- and E2+P4-treated animals released 3- to 5-fold more RBP into the medium than control and P4 treatments as determined by ELISA. RBP synthesis of metabolically labeled RBP was increased by E2 and E2+P4 treatments. This study demonstrates that P4 applied on an estradiol background negatively regulates RBP gene expression in the oviduct whereas estradiol appears to stimulate RBP synthesis and secretion.  (+info)

Onset of nucleolar and extranucleolar transcription and expression of fibrillarin in macaque embryos developing in vitro. (5/6081)

Specific aims were to characterize the onset of nucleolar and extranucleolar transcription and expression of the nucleolar protein fibrillarin during preimplantation development in vitro in macaque embryos using autoradiographic and immunocytochemical techniques. Autoradiography was performed on whole embryos cultured with [3H]uridine for assessment of nucleolar (rRNA) and extranucleolar (mRNA) transcription. Expression of fibrillarin was immunocytochemically assessed in whole embryos using a primary antibody against fibrillarin and a fluorescein isothiocyanate-conjugated secondary antibody. Extranucleolar incorporation of [3H]uridine was first detected in 2-cell embryos cultured 6-10 h with [3H]uridine. Culture with alpha-amanitin prevented incorporation of label in 2-cell embryos, and treatment with ribonuclease reduced the signal to background levels, indicating that [3H]uridine was incorporated into mRNA and not rRNA or DNA. Nucleolar incorporation of [3H]uridine was not evident in pronucleate-stage or 2- to 5-cell embryos, but it was detected in one 6-cell embryo and in all 8-cell to blastocyst-stage embryos. Fibrillarin was first expressed in some 6- to 7-cell embryos, but it was consistently expressed in all 8-cell embryos. Fibrillarin was localized to the perimeter of the nucleolar precursor bodies, forming a ring that completely encapsulated these structures. Fibrillarin was not expressed in 8- to 16-cell embryos cultured with alpha-amanitin, indicating that it is transcribed, rather than recruited, at the 8-cell stage. In conclusion, in in vitro-fertilized macaque embryos developing in vitro, extranucleolar synthesis of mRNA is initiated at the 2-cell stage while the onset of nucleolar transcription occurs at the 6- to 8-cell stage, coincident with expression of fibrillarin.  (+info)

Investigation of distal aortic compliance and vasodilator responsiveness in heart failure due to proximal aortic stenosis in the guinea pig. (6/6081)

Hypotension and syncope are recognized features of chronic aortic stenosis. This study examined vasomotor responses and dynamic compliance in isolated abdominal aortae after chronic constriction of the ascending aorta. Guinea pigs underwent constriction of the ascending aorta or sham operation. Sections of descending aorta were removed for studies of contractile performance and compliance. Dynamic compliance was measured using a feedback-controlled pulsatile pressure system at frequencies of 0.5, 1.5 and 2.5 Hz and mean pressures from 40 to 100 mmHg. Chronic (149+/-6 days) aortic constriction resulted in significant increases in organ weight/body weight ratios for left ventricle (58%), right ventricle (100%) and lung (61%). The presence of heart failure was indicated by increased lung weights, left ventricular end-diastolic pressure and systemic vascular resistance, reduced cardiac output and increased levels of plasma atrial natriuretic peptide (166%), adrenaline (x20), noradrenaline (106%) and dopamine (x3). Aortic rings showed similar constrictor responses to phenylephrine and angiotensin II, but maximal vasodilator responses to acetylcholine and isoprenaline were significantly increased (144% and 48% respectively). Dilator responses to sodium nitroprusside, forskolin and cromokalim were unchanged. Compliance of all vessels decreased with increasing pulsatile frequency and to a lesser extent with increased mean pressure, but were similar in aortic-constricted and control groups. Chronic constriction of the ascending aorta resulted in heart failure and increased vasodilator responses to acetylcholine and isoprenaline in the distal aorta while dynamic compliance was unchanged. We hypothesize that increased endothelium-mediated vasodilatation may contribute to hypotension and syncope in patients with left ventricular outflow obstruction.  (+info)

Characterization of beta cells developed in vitro from rat embryonic pancreatic epithelium. (7/6081)

The present study evaluates the development and functional properties of beta cells differentiated in vitro. The authors have previously demonstrated that when E12.5 rat pancreatic rudiments are cultured in vitro in the absence of mesenchyme, the majority of the epithelial cells differentiate into endocrine beta cells. Thus, depletion of the mesenchyme provokes the expansion of endocrine tissue at the expense of exocrine tissue. The potential use of this procedure for the production of beta cells led the authors to characterize the beta cells differentiated in this model and to compare their properties with those of the endocrine cells of the embryonic and adult pancreas. This study shows that the beta cells that differentiate in vitro in the absence of mesenchyme express the homeodomain protein Nkx6.1, a transcription factor that is characteristic of adult mature beta cells. Further, electron microscopy analysis shows that these beta cells are highly granulated, and the ultrastructural analysis of the granules shows that they are characteristic of mature beta cells. The maturity of these granules was confirmed by a double-immunofluorescence study that demonstrated that Rab3A and SNAP-25, two proteins associated with the secretory pathway of insulin, are strongly expressed. Finally, the maturity of the differentiated beta cells in this model was confirmed when the cells responded to stimulation with 16 mM glucose by a 5-fold increase in insulin release. The authors conclude that the beta cells differentiated in vitro from rat embryonic pancreatic rudiments devoid of mesenchyme are mature beta cells.  (+info)

Long-term effects of prior heat shock on neuronal potassium currents recorded in a novel insect ganglion slice preparation. (8/6081)

Brief exposure to high temperatures (heat shock) induces long-lasting adaptive changes in the molecular biology of protein interactions and behavior of poikilotherms. However, little is known about heat shock effects on neuronal properties. To investigate how heat shock affects neuronal properties we developed an insect ganglion slice from locusts. The functional integrity of neuronal circuits in slices was demonstrated by recordings from rhythmically active respiratory neurons and by the ability to induce rhythmic population activity with octopamine. Under these "functional" in vitro conditions we recorded outward potassium currents from neurons of the ventral midline of the A1 metathoracic neuromere. In control neurons, voltage steps to 40 mV from a holding potential of -60 mV evoked in control neurons potassium currents with a peak current of 10.0 +/- 2.5 nA and a large steady state current of 8.5 +/- 2.6 nA, which was still activated from a holding potential of -40 mV. After heat shock most of the outward current inactivated rapidly (peak amplitude: 8.4 +/- 2.4 nA; steady state: 3.6 +/- 2.0 nA). This current was inactivated at a holding potential of -40 mV. The response to temperature changes was also significantly different. After changing the temperature from 38 to 42 degrees C the amplitude of the peak and steady-state current was significantly lower in neurons obtained from heat-shocked animals than those obtained from controls. Our study indicates that not only heat shock can alter neuronal properties, but also that it is possible to investigate ion currents in insect ganglion slices.  (+info)