Biomedical subjects

G Singh

Publications and source records attributed to G Singh.

At least 19 recordsLinked to original sources

PubMed1992

Dominant mutation of the murine Hox-2.2 gene results in developmental abnormalities.

Genes carrying the homeobox were originally identified in Drosophila, in which they are now known to play key roles in establishing segmentation patterns and in determining segment identities. A number of genes with striking homology to the Drosophila homeobox genes have now been found in the mouse genome, and mutational analysis is beginning to shed light on their function in mammalian development. To understand better the developmental significance of the murine Hox-2.2 gene, we have generated gain of function mutants by using the chicken beta-actin promoter to drive ubiquitous expression in transgenic mice. The resulting Hox-2.2 misexpression produces early postnatal lethality as well as craniofacial and axial skeletal perturbations that include open eyes at birth, cleft palate, micrognathia, microtia, skull bone deficiencies, and structural and positional alterations in the vertebral column. We repeatedly observe complete or partial absence of the supraoccipital bone and malformations of the exoccipital and the basioccipital bones. These results suggests a role for the Hox-2.2 gene in specifying positional identity along the anterior-posterior axis.

Abnormalities, Multiple↗

PubMed1992

Truncated glucagon-like peptide-1 interacts with exendin receptors on dispersed acini from guinea pig pancreas. Identification of a mammalian analogue of the reptilian peptide exendin-4.

To find mammalian analogues of exendin-4, a peptide from Helodermatidae venoms that interacts with newly discovered exendin receptors on dispersed acini from guinea pig pancreas, we examined the actions of recent additions to the vasoactive intestinal peptide/secretin/glucagon family of regulatory peptides. In every respect tested, the truncated form of glucagon-like peptide-1, GLP-1(7-36)NH2, mimicked the actions of exendin-4. Like exendin-4, GLP-1(7-36)NH2 caused an increase in acinar cAMP without stimulating amylase release. GLP-1(7-36)NH2-induced increases in cAMP were inhibited progressively by increasing concentrations of the specific exendin-receptor antagonist, exendin(9-39)NH2. In dispersed acini from guinea pig and rat pancreas, concentrations of GLP-1(7-36)NH2 that stimulated increases in cAMP caused potentiation of cholecystokinin-induced amylase release. Binding of 125I-[Y39]exendin-4 or 125I-GLP-1(7-36)NH2 to dispersed acini from guinea pig pancreas was inhibited by adding increasing concentrations of unlabeled exendin-4 or GLP-1(7-36)NH2. We conclude that the mammalian peptide GLP-1(7-36)NH2 interacts with exendin receptors on dispersed acini from guinea pig pancreas. Exendin(9-39)NH2, a competitive antagonist of the actions of GLP-1(7-36)NH2 in pancreatic acini, may be a useful tool for examining the physiological actions of this peptide.

Amino Acid Sequence↗

PubMed1992

cis-acting elements that confer lung epithelial cell expression of the CC10 gene.

To define cis-acting genetic elements responsible for cell-specific transcriptional regulation of the CC10 gene, DNA sequences spanning nucleotides -2338 to +49 of the rat CC10 gene were linked to a reporter gene coding for chloramphenicol acetyltransferase (CAT). In transient expression assays, CC10 sequences were capable of restricting CAT expression to a human lung adenocarcinoma cell line similar to pulmonary Clara cells. Transgenic mice harboring the hybrid RtCC10-CAT construct expressed high levels of CAT activity specifically within protein extracts of lung and trachea. Transcripts for the CAT reporter gene colocalized with those for the endogenous murine CC10 gene within the airways of transgenic mice. Functional analysis of deletion mutants identified stimulatory, inhibitory, and cell type-specific transcriptional regulatory elements. The results of gel retention and DNaseI protection assays suggest that a transcriptional stimulatory region located between -320 and -175, and a cell type-specific regulatory element located between -175 and +49, result from a series of protein-DNA interactions occurring at -220 to -205 and -128 to -86, respectively. Lung epithelial specific transcriptional regulatory elements described herein will be useful for expression of chimeric genes within epithelial cells lining the trachea, bronchi, and bronchioles of mice.

Adenocarcinoma↗

PubMed1992

Isolation and characterization of exendin-4, an exendin-3 analogue, from Heloderma suspectum venom. Further evidence for an exendin receptor on dispersed acini from guinea pig pancreas.

The recent identification in Heloderma horridum venom of exendin-3, a new member of the glucagon superfamily that acts as a pancreatic secretagogue, prompted a search for a similar peptide in Heloderma suspectum venom. An amino acid sequencing assay for peptides containing an amino-terminal histidine residue (His1) was used to isolate a 39-amino acid peptide, exendin-4, from H. suspectum venom. Exendin-4 differs from exendin-3 by two amino acid substitutions, Gly2-Glu3 in place of Ser2-Asp3, but is otherwise identical. The structural differences make exendin-4 distinct from exendin-3 in its bioactivity. In dispersed acini from guinea pig pancreas, natural and synthetic exendin-4 stimulate a monophasic increase in cAMP beginning at 100 pM that plateaus at 10 nM. The exendin-4-induced increase in cAMP is inhibited progressively by increasing concentrations of the exendin receptor antagonist, exendin-(9-39) amide. Unlike exendin-3, exendin-4 does not stimulate a second rise in acinar cAMP at concentrations greater than 100 nM, does not stimulate amylase release, and does not inhibit the binding of radiolabeled vasoactive intestinal peptide to acini. This indicates that in dispersed pancreatic acini, exendin-4 interacts only with the recently described exendin receptor.

Amino Acid Sequence↗

PubMed1992

Refined structure of rat Clara cell 17 kDa protein at 3.0 A resolution.

The rat Clara cell 17 kDa protein (previously referred to as the rat Clara cell 10 kDa protein) has been reported to inhibit phospholipase A2 and papain, and to also bind progesterone. It has been isolated from rat lung lavage fluid and crystallized in the space group P6(5)22. The structure has been determined to 3.0 A resolution using the molecular replacement method. Uteroglobin, whose amino acid sequence is 55.7% identical, was used as the search model. The structure was then refined using restrained least-squares and simulated annealing methods. The R-factor is 22.5%. The protein is a covalently bound dimer. Two disulfide bonds join the monomers together in an antiparallel manner such that the dimer encloses a large internal hydrophobic cavity. The hydrophobic cavity is large enough to serve as the progesterone binding site, but access to the cavity is limited. Each monomer is composed of four alpha-helices. The main-chain structure of the Clara cell protein closely resembles that of uteroglobin, but the nature of many of the exposed side-chains differ. This is true, particularly in a hypervariable region between residues 23 and 36, and in the H1H4 pocket.

Amino Acid Sequence↗

PubMed1992

A quantitative model for spontaneous bone metastasis: evidence for a mitogenic effect of bone on Walker 256 cancer cells.

A new model for the study of spontaneous bone metastasis has been developed which allows for the quantification of metastatic tumor burden and cancer cell growth rate, and which describes the progressive changes in bone morphology. Walker 256 (W256) cells or vehicle were injected into the left upper thigh muscle of male Fischer rats, which were killed 7, 10 or 14 days later. By day 7, metastases had appeared in the distal femur, in the glomeruli of the kidney, and diffusely throughout the liver and lungs. The extent of tumor burden in these organs increased over time. In the femur, 14 days of tumor burden was associated with a 53 +/- 10% decrease in trabecular bone content, a 61 +/- 15% increase in osteoclast surface, and a 95 +/- 10% decrease in osteoblast surface, as compared with non-tumor-bearing controls. By autoradiography, metastatic tumor cells in all organs were determined to have greater growth rates than did cells in the primary tumor. However, within the femur, W256 cells located adjacent to trabecular bone surfaces had a 33 +/- 7% greater growth rate than did W256 cells located > 50 microns from bone surfaces (P < 0.05), suggesting a mitogenic effect of bone.

Animals↗

PubMed1992

Stimulation of bone resorption results in a selective increase in the growth rate of spontaneously metastatic Walker 256 cancer cells in bone.

To test the hypothesis that bone metastasis is related to the rate of bone remodeling, we have examined the effect of enhanced bone resorption on the growth of spontaneously metastatic Walker 256 (W256) cancer cells. Bone resorption was stimulated in male Fischer rats by injecting Rice H-500 Leydig tumor cells subcutaneously. The resorptive response of the skeleton was confirmed in a pilot study by evaluating parameters of bone morphometry after 4, 7 and 10 days of tumor burden. The distal femoral epiphyses had 35 +/- 10% more osteoclast surface, 83 +/- 11% less osteoblast surface, and 46 +/- 5% less trabecular bone after 10 days of tumor burden, compared to non-tumor-bearing controls. To evaluate the effect of Leydig tumor-induced bone resorption on the growth response of W256 cells, 20 rats were injected intramuscularly with 2 x 10(7) W256 cells, and 20 rats were vehicle-injected. Two days later, 10 rats from each group were injected subcutaneously with Leydig tumor cells. Twelve days after W256/vehicle injection, rats were injected with [3H]thymidine, killed 2 h later, and their femurs, liver, lungs and kidneys were processed for histology. In rats injected with Leydig tumor cells only, enhanced bone resorption was confirmed by a 40 +/- 4% increase in serum calcium concentration, a 48 +/- 8% decrease in trabecular bone content, and a 72 +/- 15% decrease in osteoblast surface, compared with non-tumor-bearing rats. Metastatic W256 cells adjacent to trabecular bone in Leydig tumor-bearing rats had a 56 +/- 18% greater relative [3H]thymidine labeling index (TdR) than did W256 cells in the bones of non-Leydig tumor-bearing rats. The TdRs of W256 cells in the liver, lungs, and kidneys were not affected by Leydig tumor burden. In this model, enhanced bone resorption was associated with the selective growth promotion of metastatic W256 cells in bone, suggesting the existence of a bone-derived factor which is mitogenic to W256 cells.

Animals↗

PubMed1992

Omeprazole-induced hypergastrinemia does not influence growth of colon carcinoma.

Colonic mucosa and adenocarcinoma are known to possess gastrin receptors. Recent studies have suggested that some patients with large intestinal cancers and polyps have elevated serum gastrin levels and that gastrin may stimulate growth of colonic neoplasms. The aim of the present investigation was to determine whether endogenous hypergastrinemia--induced by the proton pump inhibitor omeprazole--would influence growth in a subcutaneously implanted murine colonic cancer. The results show that despite a fivefold increase in serum gastrin levels (193 pg/ml median value, range 186-252, in the omeprazole-treated group vs 36 pg/ml median value, range 28-37 in controls), there were no differences in tumor size or survival of tumor-bearing animals. Additionally, there were no differences in serum gastrin values between tumor- (29 pg/ml, range 25-38) and non-tumor- (34 pg/ml, range 25-30) bearing, untreated animals. Endogenous elevation of the serum gastrin hormone to five times the normal level does not demonstrate trophic effects on the murine colon tumor MC-26.

Adenocarcinoma↗

PubMed1992

The regulated expression of mRNA for Clara cell protein in the developing airways of the rat, as revealed by tissue in situ hybridization.

Tissue in situ hybridization has been used on sections of developing rat lung to follow the cellular sites of mRNA expression for a protein identified only in bronchiolar Clara cells. The mRNA for this Clara cell protein (CCP) was first detected on gestational day 16 in only one of the two types of tubules existing in the lung at this developmental stage. During the next 2 days CCP mRNA expression increased uniformly only in the epithelium lining the respiratory tubules. By gestational day 19, CCP mRNA expression became limited to secretory epithelial cells lining the bronchi, and terminal bronchioles. By neonatal day 1, an intense hybridization signal was observed along all of the conducting airways, but it was irregular due to the fact that expression of the CCP gene was limited to the secretory epithelial cells. In adult rats, CCP mRNA was expressed not only in secretory cells of the intrapulmonary airways at all anatomical levels, but also in secretory epithelial cells lining the trachea and its glands, as well as in specific alveolar cells thought to be type II pneumocytes. These findings demonstrate that the regulation of the CCP gene during lung development is a complicated process and that the expression of CCP mRNA does not parallel exactly the sequential development of the airways.

Animals↗

PubMed1992

Humoral responses to type I collagen after surgical curettage procedures employing bovine collagen implants.

Freeze-dried bovine type I collagen was implanted into periodontally diseased sites of 11 patients in an effort to repair the affected site. Peripheral blood samples taken at 0, 6 and 12 wk were assayed for antibody to human and bovine collagen using an enzyme-linked immunosorbent assay and compared with samples from 9 control subjects. Antibody levels to both human and bovine collagen, which were present at significantly higher levels in the patients at 0 wk than in the control subjects (P less than 0.01 for human and bovine), were significantly lower at 6 wk than at zero time (P less than 0.05 and P less than 0.01 for human and bovine collagens, respectively). At 12 wk post-implantation, the antibody level to human collagen still remained significantly lower (P less than 0.05) than zero time levels but not in respect of the antibody to bovine collagen.

Adult↗

PubMed1992

Mitochondrial DNA damage by anticancer agents.

Mitochondrial DNA (mtDNA) is susceptible to damage by a number of anticancer agents either directly or indirectly. This damage is of little consequence if only a few of the mtDNA molecules are damaged. However, multiple drug treatments could result in a significant effect on a cell's ability to survive. The differential effect of anticancer agents on either organ specific toxicities or selective tumor kill can be partially accounted for by differential mtDNA content of cells and on the basis of differential protective mechanisms within mitochondria of various organs or tumor tissue. The concept of damage to mitochondria, especially its genome, is a subject of active investigation in various laboratories. This area of research may provide mechanism(s) by which organ specific toxicities or tumor specific toxicities may be elaborated. Also, the concept of targeting tumor specific mitochondria and/or mtDNA by anticancer agents is very attractive but has not come to fruition due to a lack of understanding of the regulation of the genome in tumor cells. Future investigations in this arena will enhance our knowledge on the interaction between anticancer agents and extranuclear DNA.

Animals↗

PubMed1992

Phenytoin as a coanalgesic in cancer pain.

The efficacy of phenytoin (PHT), buprenorphine (Bu), and Bu+PHT for the relief of cancer pain of various etiologies was evaluated in a randomized, double-blind study of 3 groups, each comprised of 25 patients. Treatment duration was 1 month. PHT (100 mg by mouth twice daily) provided greater than 50% pain relief to 18 patients (72%) and greater than 75% relief to 4 (16%). Bu (0.2 mg sublingually twice daily) gave 21 patients (84%) greater than 50% relief and 15 patients (60%) greater than 75% relief. Of the Bu-treated patients, 8 had major side effects, while none of the PHT-treated patients experienced significant untoward reactions. Combined therapy (PHT, 50 mg PO+Bu 0.1 mg SL twice daily) provided greater than 50% pain relief to 22 patients (88%) and greater than 75% to 18 (72%); only 3 patients experienced a significant side effect. This study suggests that phenytoin has mild-to-moderate pain-relieving properties of its own and can significantly enhance buprenorphine analgesia. By permitting a lower opioid dose, it may reduce the occurrence of opioid-related side effects. PHT's lack of serious side effects, as well as its documented anxiolytic and antidepressant actions, may add to its comparative usefulness. Further clinical trials of PHT as a coanalgesic and/or adjuvant agent in cancer pain are warranted.

Adult↗

PubMed1992

Aetiology of chronic leg ulcers.

This study was undertaken to determine the relative prevalence of the factors causing chronic ulceration of the leg in the general population. Two hundred and fifty-nine patients with chronic ulceration of the leg were found on screening a Western Australian population of 238,000. (The prevalence of chronic ulceration of the leg was 1.1 per 1000 population.) Two hundred and forty-two of these patients (93%) with 286 chronically ulcerated limbs were fully assessed to determine the factors contributing to ulceration. In 239 limbs (84%) ulceration involved the leg; in these limbs venous disease was the most prevalent cause of ulceration (160 limbs). Arterial disease was found in 66 limbs, with both venous and arterial disease present in 35 limbs. Rheumatoid arthritis was a causative factor in 27 limbs and diabetes was found with 29 limbs with ulceration involving the leg. In 47 limbs (16%) ulceration was confined to the foot; arterial disease (35 limbs) and diabetes (23 limbs) were the most prevalent causes of ulceration in these limbs. Venous disease was infrequent (three limbs). No disorder of the circulation was found in 48 limbs (20%) with ulceration involving the leg, and in 58 (20%) of all ulcerated limbs. More than one aetiological factor was present in 93 limbs (33%). A cause for ulceration was not found in 10 limbs (3.5%).

Adult↗

PubMed1992

Translocation of aged cyclodiene insecticide residues from soil into forage crops and pastures at various growth stages under field conditions.

Field trials were conducted to measure translocation of pesticides by summer and winter forage/pasture species from soil containing aged residues of heptachlor and, to a lesser extent, dieldrin. Substantial amounts of heptachlor epoxide, and lesser amounts of gamma-chlordane were translocated to plants from contaminated soil. Residue levels varied with crop species and stage of plant development. In summer crops residues were higher in soybean > cowpeas > lab-lab > Sorghum > millet > sweet saccaline at the grazing and mature stages. Compared to glasshouse studies undertaken previously, residues in crops grown under field conditions were much lower. This apparently reflects the lower soil moisture levels and the reduced rates of translocation. Heptachlor residues in winter crops were highest in Saia oats > Berseem clover > Haifa clover > Cassia oats > Tetila ryegrass > Schooner barley > Shaftal clover > Hunter river lucerne at the grazing stage. There were no detectable levels in barley and oats at the mature stage. No dieldrin residues were translocated into the various crop species.

Animal Feed↗

PubMed1992

Papillary adenoma of the lung.

Three cases of an unusual neoplasm of the lung appeared as solitary, peripheral pulmonary nodules in asymptomatic patients. These well-circumscribed neoplasms were composed of distinctive papillae covered by uniform cuboidal to columnar cells; more solid areas often were present. Ciliated cells, epithelial mucin, and necrosis were not observed, and mitotic activity was absent. Terminal tight junctions and microvilli were present in the two cases studied ultrastructurally. One specimen contained lamellar bodies and apical cytoplasmic dense bodies. Another case stained positively for a Clara cell-specific antigen, although surfactant apoprotein was not detected by immunostaining in the three cases. All patients have been free of disease (at 11 to 108 months). Papillary adenoma is an uncommon, apparently benign, and morphologically distinctive neoplasm. The immunohistochemical and ultrastructural findings hint at an origin from type II pneumocytes or Clara cells.

Adult↗

PubMed1992

Crystalloid is as effective as blood in the resuscitation of hemorrhagic shock.

Recently there has been increasing concern over transfusion-related diseases, especially acquired immune deficiency syndrome (AIDS). The authors therefore investigated the efficacy of lactated Ringer's solution (LRS) alone as compared with blood plus LRS resuscitation on body weight change and mortality rate after severe trauma-hemorrhagic shock. Rats, 250 to 310 g (n = 85), had a midline laparotomy performed (i.e., trauma induced), the incision was closed, and a carotid artery, jugular vein, and femoral artery were cannulated. The unrestrained, nonheparinized rats were allowed to recover from anesthesia and were bled within 10 minutes to a mean arterial pressure (MAP) of 40 mmHg. This MAP was maintained by removing more blood until the animal was unable to compensate (maximal bleedout; MB). The MAP was further maintained at 40 mmHg by returning fluid (LRS) until 50% of the MB volume (MBV) was returned. The rats were then resuscitated: group 1 with LRS 4 times the MBV; group 2 with 5 x LRS; group 3 with the shed blood returned + 2 x LRS. There was no difference between the groups in the initial weights, MAP, or hematocrit (Hct), percentage of blood volume removed, time to MB, or time to end of hemorrhage. The final Hct and MAP were higher in group 3 (p less than 10(-6)) than in either of the other groups. Body weight gain was greater in group 2 compared with either of the other groups (p less than 0.05) on day 1 after hemorrhage because of edema, but no differences were seen on subsequent days. There were no differences in the survival of animals in the different groups. These results suggest that there should perhaps be a higher threshold for blood transfusion in the management of severe trauma-hemorrhagic shock than is currently practiced.

Animals↗

PubMed1992

Protective effects of preheparinization on the microvasculature during and after hemorrhagic shock.

Despite the fact that trauma patients are not heparinized at the time of injury, most models of hemorrhagic shock involve heparinization before the initiation of hemorrhage. To determine whether preheparinization has any effects on the microvasculature of organs during or after hemorrhage, rats (with and without preheparinization) were bled to a mean arterial blood pressure (BP) of 40 mm Hg. In two groups, this pressure was maintained by withdrawing additional blood until BP could no longer be maintained at 40 mm Hg (maximal bleedout, MB). In another two groups, the BP was maintained at 40 mm Hg until 40% of the MB volume was returned in the form of lactated Ringer's solution. The rats were then resuscitated with four times the volume of MB with lactated Ringer's. At MB or immediately after resuscitation, colloidal carbon black was rapidly infused and the liver, kidney, and spleen were excised, fixed, and sectioned. In additional animals, blood samples for platelet counts and total body fibrinogen estimates were taken before hemorrhage and at MB or at the end of resuscitation. The results indicate that at MB, microvascular patency in the kidney and liver was significantly depressed in the nonheparinized rats but not depressed in the preheparinized rats. This protective effect of heparin is not directly attributable to its anticoagulant properties, since there were no differences in the consumption of platelets or fibrinogen between the nonheparinized and preheparinized groups. Although the microvascular patency improved with resuscitation in the nonheparinized group, the glomeruli counts and perfusion of the spleen remained significantly lower than in the preheparinized group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Autoimmunity to collagen in adult periodontal disease: immunoglobulin classes in sera and tissue.

The immunoglobulin class distribution of antibody to human collagen type I has been examined in sera and gingival extracts from patients with adult chronic periodontitis. Tissue extracts were made either by simple washing or ultrasonication. With either method, IgG and IgA antibodies to collagen were present in higher concentration in tissue extracts than in autologous serum when adjustment was made for dilution differences. No significant differences were found for IgM antibodies. Antibodies to human collagen type I are usually "natural antibodies" of the IgM class and, therefore, our findings suggest a class switch to IgG in inflamed gingivae, presumably due to prolonged antigenic stimulation.

Adult↗