Biomedical subjects

W Y Chan

Publications and source records attributed to W Y Chan.

At least 163 records · Page 9Linked to original sources

PubMed1991

Regenerative capacity of forelimb buds after amputation in mouse embryos at the early-organogenesis stage.

The ability of mouse forelimb buds at stage 1 (Wanek et al., '89a) of development to regenerate after amputation was investigated. The findings were as follows: 1. Outgrowths in the form of hillocks were found at the sites of amputation in 116 (95%) out of 122 embryos examined 24 hours after amputation. Examination of the amputated region after various intervals of time revealed that the outgrowths were established from flank tissues at the anterior and posterior borders of the wound. 2. Ectodermal thickening was found on the distal margin of the outgrowths in 21 (66%) out of 32 specimens examined. These thickenings were histologically similar to the apical ectodermal ridge (AER) present on the control limb buds. 3. Alkaline phosphatase activity was detected on the ectodermal thickening in 11 (79%) out of 14 experimental limb buds examined. The pattern of expression of alkaline phosphatase activity was similar to that observed in control limb buds. 4. There was no correlation between the size of the outgrowths and the presence of the ectodermal thickening or the enzymatic activity. The outgrowths developed despite the absence of ectodermal thickening and enzymatic activity, suggesting that the thickening and the presence of alkaline phosphatase are not crucial for the initiation and formation of the outgrowths. 5. Explants of the outgrowths, when grafted beneath adult kidney capsules, differentiated extensively into various tissues, which included bones, epiphyseal plates, skeletal muscles, and skin derivatives. Control explants also gave rise to the same spectrum of tissues. Hence, the flank tissues surrounding the site of amputation in E10 mouse embryos can regenerate to form a structure that is morphologically and histochemically similar to a limb bud and the mesenchyme within the structure is histogenetically competent to produce the variety of tissues that is normally found in the adult limb.

Alkaline Phosphatase↗

PubMed1991

A study on the regenerative potential of partially excised mouse embryonic fore-limb bud.

The ability of day E10 mouse fore-limb bud to regulate following the removal of a portion of limb tissue was investigated. A longitudinal strip of tissue, two to three somites in width and extending from the base of the limb bud to its distal tip, was excised. The embryos were then maintained in a roller culture system for periods of 6 h, 12 h or 24 h post-operatively prior to fixation and subsequent examination. The embryos were examined with scanning electron microscopy (SEM) and light microscopy. SEM revealed that about two thirds of the operated limbs grossly restored their overall morphology. The sequence of morphological changes involved in the restoration process is described. The ability of the restored limb bud to develop an apical ectodermal ridge (AER) is shown in histological sections.

Animals↗

PubMed1991

Trichosanthin induces atresia of ovarian follicles and inhibits steroidogenesis in gonadotropin-primed immature mice.

1. Immature mice were induced to ovulate by injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin spaced 48 hr apart. 2. Trichosanthin (TCS), a protein purified from tubers of Trichosanthes kirilowii (Family Cucurbitaceae), was administered respectively 24 hr before, on the same day as, 24 hr after and 48 hr after the PMSG injection. 3. The results of TCS injections at different times were generally similar. The number of maturing follicles, corpora lutea and ovulated oocytes, and the ovarian weight, remained unaltered. 4. However, there was an increased incidence of follicular atresia and degeneration of ovulated oocytes, and a lowering of serum estradiol-17 beta and progesterone levels.

Animals↗

PubMed1991

Localization of pregnancy-specific beta 1-glycoprotein in the male reproductive tract of the rat by in situ hybridization.

Human pregnancy-specific beta 1-glycoprotein (PSG) is found in high concentrations in the serum of pregnant women, but also has been found in the serum of males and nonpregnant females. Northern slot-blot analysis has demonstrated the presence of PSG mRNA in a variety of tissues in the rat, with the highest levels being found in the testis. Therefore, we have investigated further the expression of PSG in the rat male reproductive tract using in situ hybridization. In testes from immature and adult rats, PSG mRNA was localized in Leydig and peritubular cells, and in the walls of the interstitial blood vessels. PSG transcripts were noted also in the tunica albuginea and in the stromal tissue of the caput and cauda epididymis, prostate, and seminal vesicle from adult rats. The function of PSG is unknown, but it has been speculated that PSG may have immunosuppressive properties or that it may serve as a paracrine regulator of growth and differentiation. It is possible, then, that PSG could contribute to the immunological privilege of the testis or that it plays a role in the cellular interactions which increasingly are being shown to be important in the regulation of male reproductive tract tissues.

Animals↗

PubMed1991

Epithelial damage by Helicobacter pylori in gastric ulcers.

On review of 136 consecutive biopsies of benign gastric ulcer, Helicobacter pylori was detected in 78 cases (57.3%). The gastric epithelium colonized by Helicobacter pylori showed a characteristic constellation of changes, including loss of apical mucous portion of individual cells, drop-out of epithelial cells, epithelial pits, erosions and cellular tufts, indicative of cellular injury and regeneration. Among the 58 Helicobacter-negative cases, similar changes were not observed in the ulcer edges, except for two cases which exhibited some cellular tufts. Thus, the topographic association of Helicobacter pylori with epithelial damage in the gastric ulcer edges in more than half of the cases suggests that this organism probably plays an aetiological role in ulcerogenesis, at least in these cases. Furthermore, the epithelial changes are so distinctive that they can serve as a helpful histological indicator for the presence of Helicobacter pylori in gastric biopsies.

Adult↗

PubMed1991

Oxytocin antagonists with changes in the Asn5 position shed light on hormone-oxytocin receptor interactions.

Since oxytocin agonists and antagonists have different structure-activity relationships, we have investigated the stereostructural and stereoelectronic requirements of the Asn5 residue in oxytocin antagonists by the synthesis of four analogues of the potent, prolonged acting oxytocin antagonist [Pen1,D-Phe2,Thr4,Orn8]-oxytocin (I) in which Asn5 was replaced respectively with Thr (II), Leu5 (III), Asp5 (IV) and Tyr5 (V). These analogues had pA2 values in the antioxytocic in vitro rat uterine assay of 7.23 (I), 7.16 (II), 6.67 (III), 7.21 (IV), and 6.76 (IV), respectively. All were also found to be weakly potent in the in vivo anti-vasopressor assay in the rat. These studies demonstrate very different structural and stereoelectronic requirements for oxytocin agonists and antagonists when they interact with the oxytocin uterine receptor.

Amino Acid Sequence↗

PubMed1991

Effects of inactivation of oxytocin receptor and inhibition of prostaglandin synthesis on uterine oxytocin receptor and gap junction formation and labor in the rat.

Normal term labor is associated with a surge in myometrial oxytocin receptor formation and gap junction development. We have previously shown that inhibition of prostaglandin synthesis by naproxen sodium, 2.0 mg/day, suppressed oxytocin receptor formation but not gap junction formation and prolonged gestation. In this study, we investigated the effects of a specific oxytocin antagonist on oxytocin receptor formation, gap junction formation, and labor in the rat. [Pen1,Phe(Me)2,Thr4,Orn8]oxytocin, a specific oxytocin antagonist, was infused subcutaneously during the last 3 days of pregnancy at 300 micrograms/day. Measurements of myometrial oxytocin receptor concentrations and gap junction formation on days 21 and 22 and days 22-23 (in labor) pregnant uteri showed no significant differences in the Bmax and Kd values between the control and the treated group. Gestation period was not prolonged by the oxytocin antagonist. However, in a separate group of day 23 pregnant rats, the uterine contractile response to 60 mU of oxytocin i.v. was found completely blocked by 10 micrograms of the oxytocin antagonist. These findings suggest that although functional oxytocin receptors did not appear to be essential for the initiation of labor, oxytocin antagonists may still be effective in the prevention of premature contractions. We also examined the effects of a higher dose of naproxen sodium, 5.0 mg/day, on gap junction formation. At this dose, naproxen sodium suppressed both oxytocin receptor and gap junction formation, prolonged gestation, and delayed parturition by 24 h or longer. Prostaglandin appears to be an important regulator or mediator of oxytocin receptor and gap junction formation and plays a critical role in the initiation of labor.

Angiotensin Receptor Antagonists↗

PubMed1991

Shivering during regional anaesthesia and its control with pethidine.

Ninety-seven consecutive patients who underwent four different types of regional anaesthesia such as lumbar epidural, spinal, caudal and brachial blocks were studied for their incidence of shivering. Fifty percent of patients who received epidural anaesthesia shivered compared to 19% of patients who received either spinal or caudal anaesthesia. None of the patients who had brachial block shivered. Intravenous injection of 25 mg pethidine would stop shivering in almost all patients who shivered during regional blocks.

Adult↗

PubMed1991

Intraocular growth and differentiation of tissue fragments isolated from primitive streak-stage mouse embryos.

Small tissue fragments were isolated from 5 different regions of mouse embryos at the primitive streak-stage and were grafted ectopically into the anterior eye chambers of syngeneic adult mice. Of the grafts, 22-66% became attached to the iris and were vascularised within 2-3 days. The attached grafts grew in size and formed loose aggregates of embryonic cells. During the fourth week in oculo, fully differentiated tissues representing derivatives of all three germ layers were found within the grafts. No differences in the composition of tissues derived were observed in grafts obtained from different regions of the embryo except that the endodermal grafts formed endodermal cysts only. The size of the original fragments did not affect their in oculo differentiation but smaller fragments had a lower chance of intraocular survival.

Animals↗

PubMed1990

Characterization of cDNAs of the human pregnancy-specific beta 1-glycoprotein family, a new subfamily of the immunoglobulin gene superfamily.

Three highly homologous cDNAs encoding human pregnancy-specific beta 1-glycoprotein (SP1) were isolated from a human placental cDNA library. These cDNAs share greater than 90% nucleotide homology in their coding sequences, and greater than 79% of the encoded amino acids are homologous. Proteins encoded by these cDNAs are very similar to members of the carcinoembryonic antigen family and contain repeating domains, conserved disulfide bridges, and beta-sheet structure typical of the immunoglobulin gene superfamily. However, the high degree of sequence homology and relatively lesser degree of glycosylation among the SP1 proteins suggest that they exist as a unique family instead of being members of the CEA family. Both soluble and potentially membrane-bound forms of SP1 proteins were present in the placenta. Northern blot analysis using specific probes confirmed the expression of multiple mRNA species in human term placenta.

Amino Acid Sequence↗

PubMed1990

Expression of the pregnancy-specific beta 1-glycoprotein genes in human testis.

Northern blot analysis with placental pregnancy-specific beta 1-glycoprotein (SP1) cDNA probe showed the presence of SP1 mRNAs in human testis. Presence of translational products of the mRNAs was demonstrated by Western blot analysis with anti-human SP1 antibodies albeit difference in mobilities between the testis and placental proteins was apparent. Screening of human testis cDNA library with placental SP1 probe yielded 4 groups of positive clones. Two groups were identical to human placental SP1 cDNAs previously reported. The other 2 groups consisted of cDNA of incompletely processed mRNAs. These 2 groups were present in high abundance. Sequence analysis suggested that the cDNAs were products of different genes.

Amino Acid Sequence↗

PubMed1990

Molecular biology of adrenergic and dopamine receptors and the study of developmental nephrology.

Neurotransmitters convey specific messages by binding to receptors on the cell membrane surface. Receptors are linked to membrane-bound, signal-transducing proteins which act as intermediaries in the generation of second messengers that elicit biological responses. Cell surface receptors could be grouped into families that utilize common systems for their signal transmission. These classes include the growth factor receptors, the transporter receptors which internalize their ligands, ion channels, and G-protein-coupled receptors. In the past few years, the cDNAs and/or genes of a number of G-protein-coupled receptors have been cloned. Structural analysis of the G-protein-coupled receptors, as well as the other classes of receptor, shows that those receptors which use a common signaling pathway have similar topographies and share significant sequence homology. Adrenergic and dopamine receptors are examples of receptors coupled to G proteins. This review outlines some strategies in the study of adrenergic and dopamine receptors using molecular biology techniques and how they relate to investigations in developmental nephrology.

GTP-Binding Proteins↗

PubMed1990

Effects of conformational constraint in 2- and 8-cycloleucine analogues of oxytocin and [1-penicillamine] oxytocin examined by circular dichroism and bioassay.

The analogues of oxytocin and [1-penicillamine]oxytocin, containing a cycloleucine (Cle) residue in position 2 or 8, were investigated by means of circular dichroism measurements in different solvents, and the results examined in terms of their biological activities. A cycloleucine residue in position 2 substantially reduces the free conformational space of the hormone 20-membered ring moiety (including the disulfide group), and stabilizes a conformation which is close to one of the possible conformations of oxytocin and involves a beta-turn. In position 8, the Cle residue affects the conformation of the Tyr2 side chain, apparently forcing it away from the space above the 20-membered disulfide ring. However, it does not appear that the Cle residue has any significant effect on the overall backbone conformation of the hormone. The steric effect of the penicillamine residue in position 1 on the conformation of the disulfide group and Tyr2 side chain from previous investigations is further confirmed. The synthesis and biological potency of [1-penicillamine, 8-cycloleucine]oxytocin is described. This analogue exhibits a strong inhibitory effect on the uterotonic activity of oxytocin in vitro. It also inhibited the vasopressor response to vasopressin.

Animals↗

PubMed1990

Pregnancy-specific beta 1-glycoprotein messenger ribonucleic acid and immunoreactive protein in the rat testis.

Human pregnancy-specific beta 1-glycoprotein (PS beta G) is synthesized in large quantities by syncytiotrophoblasts of the placenta. Recent studies using a partial cDNA of PS beta G isolated from human term placenta detected the presence of mRNA highly homologous to placental PS beta G in a number of extraplacental tissues, including human and rat testis. The present study determined in the rat that the amount of PS beta G mRNA based on percentage of total tissue RNA was greatest in the testis of mature rats, followed by senescent and prepubertal rats. In experiments using rats with testicular feminization syndrome (Tfm) which exhibit end-organ insensitivity to androgen stimulation, slot blot analysis of testicular RNA showed reduced levels of PS beta G mRNA in Tfm rats compared to normal rats. Northern blot analysis of rat testicular RNA probed with a human placental PS beta G cDNA demonstrated the presence of a single mRNA species of 1.65 kilobases. Subsequent studies investigated whether proteins immunologically similar to PS beta G were present in the testes from normal and Tfm rats. The rat testes were perfused with fixative, and sections from paraffin-embedded tissues were treated with rabbit anti-human PS beta G, followed by the avidin-biotin-peroxidase complex. Testes from the normal rat showed intense immunostaining in late spermatids (steps 16, 17, 18, and 19 of spermiogenesis), residual bodies, as well as cytoplasm of Leydig cells. Spermatozoa within the epididymis also demonstrated intense immunolabeling. Paraffin sections of the testes from the Tfm rat showed light diffuse cytoplasmic immunostaining in cells of the seminiferous tubules. Since spermiogenesis does not proceed normally, and no spermatids were seen, it was not possible to accurately stage the seminiferous tubules of the Tfm rat. The Leydig cells of the Tfm testes stained intensely, however, as was observed in the testes of the normal rat. These data suggest that the rat may provide an animal model for the investigation of the biological function and regulation of PS beta G in the testis.

Animals↗

PubMed1990

Oxytocin- and vasopressin-binding sites in the rat uterus: competition binding and inhibitory pA2 studies with oxytocin and oxytocin antagonists.

Recent reports have presented evidence suggesting that there are distinct oxytocin (OT) and vasopressin (VP) receptors in the human and rabbit myometrium. In this study we have investigated whether OT and arginine vasopressin (AVP) activate the same or two different receptor systems in the rat uterus in producing their uterotonic action and whether the myometrial OT/VP receptors are similar to the V1 receptors in the vascular smooth muscle cells. We compared the dose-response characteristics of OT and AVP by the in vitro cumulative dose-response curve technique. We determined the ligand-receptor binding characteristics of [3H]OT and [3H]AVP on uterine membrane fractions from nonpregnant and pregnant rats. Specific OT antagonists were used in competition receptor binding assays and in antioxytocic pA2 bioassays against OT and AVP to determine whether OT antagonists can discriminate between OT- and AVP-binding sites in the myometrium. We also compared the in vitro antioxytocic (OT receptor-mediated action) and the in vivo antivasopressor (V1 receptor-mediated action) potencies of a series of six OT antagonists. Our results show that OT- and AVP-binding sites in the nonpregnant rat uterus have similar binding characteristics and cannot be distinguished by the dose-response study, radioligand receptor binding assays, or OT antagonists in the competition binding and pA2 assays. However, in the term pregnant parturient uterus, the two binding sites can be clearly differentiated. OT receptor density, but not AVP, was markedly increased at term pregnancy. All six OT antagonists studied in this investigation were more potent in antagonizing the uterotonic response to OT than the vasopressor response to AVP. The antioxytocic:antivasopressor potency ratios, however, were different between the antagonists, ranging from nearly equal (0.91) to low (0.1). The results above suggest that there are distinct OT- and AVP-binding sites in the rat myometrium. The myometrial OT/AVP receptors are similar to but not the same as the V1 receptors in the vascular smooth muscle cells.

Animals↗

PubMed1990

Establishment and characterization of two nasopharyngeal carcinoma cell lines.

Two human nasopharyngeal carcinoma (NPC) cell lines have been established. One derived from a 64-year-old male, and the other from a 36-year-old female Chinese patient living in Taiwan. Both were keratinizing squamous cell carcinoma in nature and designated as NPC-TW039 and NPC-TW076. Both have been grown in culture system for more than 100 passages. Single cells from both cell lines could form colonies in 0.3% soft agar. In the nude mouse transplantation experiment, both cell lines could produce tumor mass with metastasis. The karyotypic analysis showed multiple chromosomal abnormality. The number of chromosomes ranged between 76 to 109 and 80 to 105 with an average of 98 and 95, respectively. The doubling time was 10.5 hours and 10.8 hours, respectively. The NPC-TW039 cell line has been subcloned and three subclones have been obtained. Ultrastructural studies from those two cell line, three subcloned cell lines and two transplanted tumor masses, all showed two types of morphology: the dark and light cells. This morphologic difference is probably derived from the different metabolic state, but not due to an artifact. Three oncogene probes have been used to check the oncogene expression; none of those five cell lines is positive. Similarly, six Epstein-Barr virus fragments have been labeled to hybridize with NPC cellular DNA preparations, results from the Southern blotting showed no detectable Epstein-Barr virus DNA sequence.

Animals↗

PubMed1989

Characterization of the cDNA encoding human nucleophosmin and studies of its role in normal and abnormal growth.

A cDNA encoding human nucleophosmin (protein B23) was obtained by screening a human placental cDNA library in lambda gtll first with monoclonal antibody to rat nucleophosmin and then with confirmed partial cDNA of human nucleophosmin as probes. The cDNA had 1311 bp with a coding sequence encoding a protein of 294 amino acids. The identity of the cDNA was confirmed by the presence of encoded amino acid sequences identical with those determined by sequencing pure rat nucleophosmin (a total of 138 amino acids). The most striking feature of the sequence is an acidic cluster located in the middle of the molecule. The cluster consists of 26 Asp/Glu and 1 Phe and Ala. Comparison of human nucleophosmin and Xenopus nucleolar protein NO38 shows 64.3% sequence identity. The N-terminal 130 amino acids of human nucleophosmin also bear 50% identity with that of Xenopus nucleoplasmin. Northern blot analysis of rat liver total RNA with a partial nucleophosmin cDNA as probe demonstrated a homogeneous mRNA band of about 1.6 kb. Similar observations were made in hypertrophic rat liver and Novikoff hepatoma. However, the quantity of nucleophosmin mRNA is 50- and 5-fold higher in Novikoff hepatoma and hypertrophic rat liver, respectively, when compared with normal rat liver. Dot blot analysis also showed a nucleophosmin mRNA ratio of 64:5:1 in the three types of rat liver. When the protein levels were compared with Western blot immunoassays, Novikoff hepatoma showed 20 times more nucleophosmin, while only about 5 times more nucleophosmin was observed in hypertrophic rat liver than in unstimulated normal liver.

Amino Acid Sequence↗

PubMed1989

Characterization of baboon pregnancy-specific beta 1-glycoprotein.

Immunostaining of baboon placental tissues with anti-human pregnancy-specific beta 1-glycoprotein (SPI) antibodies demonstrated that an SP1-like molecule was present in the syncytiotrophoblasts. Staining was observed on the membrane and in the cytoplasm, but the nucleus was devoid of any staining. Western blot analysis further demonstrated the presence of five protein species in baboon placental extract, whereas four protein bands were detected in human placental extract. Culture medium of baboon placental villi also contained five SP1-like molecules with sizes slightly different from those present in the placental extract. Amniotic fluid and culture medium of decidua basalis and chorioamniotic tissue contained lesser quantities and fewer species of SP1-like molecules. However, an 87 kDa band was present in all samples examined. Northern blot analysis of baboon placenta with a human placental SP1 cDNA probe demonstrated the presence of a 1.65 Kb band, whereas two hybridizing bands (1.65 Kb and 2.25 Kb) were present in human placenta. Southern blot analysis of baboon genomic DNA further demonstrated the presence of multiple bands hybridizing with a human placental SP1 cDNA probe. These results showed the presence in baboons of multiple genes encoding mRNAs and proteins highly similar to human placental SP1.

Animals↗