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Biomedical subjects

L M Smith

Publications and source records attributed to L M Smith.

At least 181 records · Page 10Linked to original sources
PubMed1989

Retinoblastoma: biology, presentation, and current management.

Retinoblastoma is an uncommon ocular tumor of childhood which accounts for 5% of childhood blindness. It serves as a prototype for understanding the genetics of childhood cancer. The identification of the retinoblastoma gene has provided an explanation for the differing features of hereditary and nonhereditary retinoblastoma, as well as the potential for secondary malignancies in the hereditary cases. Management decisions are based upon the potential for useful vision, and the extent of disease including whether one or both eyes are involved. As nearly all patients present with disease confined to the globe, local control is excellent and survival exceeds 85%. Goals of management are cure of the disease, preservation of vision, and early detection and treatment of secondary malignancies in the genetically susceptible group.

Biology↗
PubMed1988

An approach to assigning in vitro potency to unfractionated and low molecular weight heparins based on the inhibition of prothrombin activation and catalysis of thrombin inhibition.

Unfractionated and low molecular weight (LMW) heparins with good antithrombotic activity invariably catalyze thrombin inhibition and inhibit the appearance of thrombin activity in contact-activated plasma. Conversely, the antithrombotic efficacy of LMW heparins decreases as their ability to catalyze thrombin inhibition and to inhibit the appearance of thrombin activity in plasma decrease. The activated partial thromboplastin time (APTT) has proven a reliable test for assaying unfractionated heparin. We therefore compared 2 unfractionated and 3 LMW heparins on the basis of the minimum concentrations required to double the APTT of normal plasma and by then determined how this anticoagulant effect was achieved. The amount of unfractionated and LMW heparin which doubled the APTT was found to be equivalent to approximately 0.25 antithrombin units. This concentration of each glycosaminoglycan completely inhibited prothrombin activation for 45 s after CaCl2 was added to contact-activated plasma; accelerated thrombin inhibition by purified antithrombin III by approximately 50-fold; and accelerated thrombin inhibition equally by antithrombin III in undiluted plasma. This concentration of the three LMW heparins increased, by approximately 70-fold, the rate of factor Xa inhibition by purified antithrombin III compared to the 50-fold increase seen with the two unfractionated heparins. These results thus suggest that tests based on the inhibition of prothrombin activation and/or on the catalysis of thrombin inhibition provide a useful basis for assigning in vitro potency to both unfractionated and LMW heparins.

Catalysis↗
PubMed1988

Semi-preparative purification of recombinant human renin and prorenin.

Chinese hamster ovary (CHO) cells, transfected with a vector containing cDNA coding for preprorenin, have been shown to secrete authentic prorenin into the culture supernatant. Purification of the expressed prorenin and purification of active renin, generated by solid-phase trypsin treatment of the conditioned media, have been achieved by conventional chromatographic methods. Scale-up of the initial steps of these procedures is described, including the use of radial-flow columns and automation with fast protein liquid chromatography valves and pumps. This semi-preparative scheme has allowed hundreds of milligrams of both proteins to be isolated.

Cell Line↗
PubMed1988

Sustained reduction of intraocular pressure in humans with the calcium channel blocker verapamil.

We investigated the effect of the calcium channel blocker verapamil on intraocular pressure in human volunteers. In the initial trial, 15 subjects with untreated ocular hypertension were tested. After a baseline measurement was obtained with applanation tonometry, a 40-microliter drop of verapamil, 1.25 mg/ml, was instilled in one eye. After 30 minutes, a second reading was taken. In a subsequent trial of 12 untreated ocular hypertensive subjects, the duration of action was determined using the same dose and method of delivery. Results showed that verapamil elicited a mean +/- S.E.M. change in intraocular pressure of -3.8 +/- 0.900 mm Hg in the treated eye, and -1.6 +/- 0.400 mm Hg in the untreated eye. This reduction was statistically different in both eyes (treated eye, P = .0007; untreated eye, P = .005). This decrease in intraocular pressure remained statistically significant when compared to predrug baseline values for up to ten hours.

Administration, Topical↗
PubMed1988

Pharmacologic pupillary modulation in the perioperative period.

The perioperative management of the pupil is essential to the success of anterior segment surgery. A new dilating regimen was tested in 65 cases of cataract extraction and intraocular lens implantation. The alpha-adrenergic agonist, phenylephrine 2.5%, was used after pretreatment with the adrenergic beta-blocker, timolol 0.5%. This treatment successfully dilated the pupil in all but three cases, was maintained by intraoperative epinephrine infusion, and was readily reversed with intraocular acetylcholine. We conclude that this pharmacologic regimen provided a successful and easily reversible mydriasis during surgery.

Acetylcholine↗
PubMed1988

Conserved cysteine and histidine residues of the avian myeloblastosis virus nucleocapsid protein are essential for viral replication but are not "zinc-binding fingers".

The nucleocapsid protein from the Rous sarcoma virus has two regions of sequence with the motif Cys-Xaa-Xaa-Cys-Xaa-Xaa-Xaa-Gly-His-Xaa-Xaa-Xaa-Cys. All retrovirus nucleocapsid proteins contain one or two of these motifs, and they represent the only conserved sequences among these proteins. Sequence analysis of nucleocapsid from avian myeloblastosis virus shows that it also contains two Cys-His sequences and, in fact, differs from the Rous sarcoma nucleocapsid protein only in three residues near the carboxyl terminus. The hypothesized role of the conserved cysteines and histidines as zinc ligands was tested experimentally. No tightly bound metal ions were detected for avian myeloblastosis nucleocapsid protein, and the molar amount of zinc in virions was less by a factor of 50 than that of the nucleocapsid protein. Added Zn2+ did not significantly affect nucleocapsid binding to poly(ethenoadenylic acid) or its secondary structure, as determined from circular dichroism. Nevertheless, the conserved cysteine and histidine residues of the Rous sarcoma (Prague-C strain) nucleocapsid protein are essential for fully functional virus, as shown by the fact that single-site substitutions of five of the six conserved cysteines and either of the two histidine residues blocked viral replication.

Avian Leukosis Virus↗
PubMed1988

Identification and characterization of mutations affecting sporulation in Saccharomyces cerevisiae.

Mutations affecting the synthesis of the sporulation amyloglucosidase were isolated in a homothallic strain of Saccharomyces cerevisiae, SCMS7-1. Two were found, both of which were deficient in sporulation at 34 degrees. One, SL484, sporulated to 50% normal levels at 30 degrees but less than 5% at 34 degrees or 22 degrees. The other, SL641, failed to sporulate at any temperature. Both mutants were blocked before premeiotic DNA synthesis, and both complemented spo1, spo3, and spo7. Genetic analysis of the mutation in SL484 indicated linkage to TRP5 and placed the gene 10 map units from TRP5 on chromosome VII. A plasmid containing an insert which complements the mutation in SL484 fails to complement SL641. We therefore conclude that these two mutations are in separate genes and we propose to call these genes SPO17 and SPO18. These two genes are (with SPO7, SPO8, and SPO9) among the earliest identified in the sporulation pathway and may interact directly with the positive and negative regulators RME and IME.

DNA, Fungal↗
PubMed1988

Auditory/phonetic categorization with the Symbion multichannel cochlear implant.

The phonetic identification ability of an individual (SS) who exhibits the best, or equal to the best, speech understanding of patients using the Symbion four-channel cochlear implant is described. It has been found that SS: (1) can use aspects of signal duration to form categories that are isomorphic with the phonetic categories established by listeners with normal auditory function; (2) can combine temporal and spectral cues in a normal fashion to form categories; (3) can use aspects of fricative noises to form categories that correspond to normal phonetic categories; (4) uses information from both F1 and higher formants in vowel identification; and (5) appears to identify stop consonant place of articulation on the basis of information provided by the center frequency of the burst and by the abruptness of frequency change following signal onset. SS has difficulty identifying stop consonants from the information provided by formant transitions and cannot differentially identify signals that have identical F1's and relatively low-frequency F2's. SS's performance suggests that simple speech processing strategies (filtering of the signal into four bands) and monopolar electrode design are viable options in the design of cochlear prostheses.

Adult↗
PubMed1988

Characterization of recombinant human prorenin and renin.

A cell line that secretes substantial quantities of recombinant human prorenin was prepared by transfecting Chinese hamster ovary cells with a gene encoding preprorenin. The prorenin was purified to homogeneity and was found to have a single amino terminus, reflecting cleavage after a typical 23 amino acid signal sequence. The purified inactive prorenin was not a substrate for active renin and was not capable of self-activation. Prorenin could be converted to renin by addition of exogenous protease, and deglycosylation of the prorenin did not alter the sensitivity to protease activation. The enzymatic activity of deglycosylated renin was kinetically identical to that of the native protein. Multimilligram quantities of recombinant human renin and prorenin were purified, providing suitable material for studies directed toward greater understanding of the function of these proteins and for structural studies such as x-ray diffraction for use in design of renin inhibitors.

Animals↗
PubMed1988

Levocabastine. Evaluation in the histamine and compound 48/80 models of ocular allergy in humans.

The efficacy of a new antihistamine, levocabastine, in alleviating the ocular allergic reactions induced by both histamine and 48/80 was evaluated in humans. Levocabastine (0.5%) was instilled in one eye of 30 volunteers, and vehicle in the contralateral eye. After 15 minutes, half of the subjects received histamine (25 mg/ml) and half, 48/80 (7.5 mg/ml). The signs and symptoms of allergy were graded clinically after 30 minutes. Compared with a buffer control, levocabastine significantly alleviated itching (P = 0.01), redness (P = 0.0156), and chemosis (P = 0.005) induced by histamine, and itching (P = 0.032) and redness (P = 0.029) induced by 48/80. The results from these pharmacologic models support the clinical use of levocabastine for the treatment of allergic conjunctivitis.

Conjunctivitis, Allergic↗
PubMed1987

Proton NMR studies of the biologically active 1-34 fragment of bovine parathyroid hormone: examination of a structural model.

Proton NMR spectra of the biologically active 1-34 fragment of bovine parathyroid hormone (bPTH) were studied as a function of pH over the range of pH 4 to 10, in buffer and in 6 M guanidine DC1. One of the histidine C-2 peaks titrated normally, with a pKa value of 6.8, but the other two histidines in this peptide had pKa values of 6.3. Denatured PTH showed only one histidine C-2 peak with a pKa of 6.7. An aliphatic peak identified as due to either a methionine or a glutamine residue also shifted with pH, and the pKa for this shift was 6.3. Finally, small but significant upfield shifts in the methyl and methylene resonances were observed as a function of pH, and when compared to the denatured peptide. These results indicate that the N-terminal domain of native PTH has considerable structure in solution, and are consistent with a theoretical model for the folding of this peptide.

Animals↗
PubMed1987

Deletion of lysine 13 alters the structure and function of parathyroid hormone.

A peptide of unknown structure was found as a side product in a commercial preparation of the 1-34 fragment of bovine parathyroid hormone (PTH). CNBr cleavage and amino acid analysis showed that this peptide is the des-lys-13 form of 1-34 bovine PTH. The peptide thus represents a deletion mutant of PTH and structure-function studies are of interest. This peptide was a full agonist in the adenylyl cyclase bioassay for PTH, but its potency was about 5% of that found for the complete 1-34 peptide. Proton NMR studies showed that the pK values for the histidine residues in the des-lys-13 form were essentially identical to those of the intact peptide. However, pH-dependent changes in the chemical shifts for the tryptophan protons (residue 23) and several unidentified methyl group resonances were observed in the des-lys peptide. The latter are major shifts and probably represent ring-current effects; these were not seen in the intact 1-34 peptide. The results show that Lys-13 is important in the folding of the active domain of PTH, and are interpreted in the context of a previously published model for the folding of this hormone.

Amino Acid Sequence↗
PubMed1987

Automated DNA sequencing and analysis of the human genome.

In the past few years, striking advances have been made in automating DNA sequence analysis. Currently, efforts are underway to automate and improve DNA purification, mapping, and data processing procedures. The predictable advances in these technologies should soon place us in a position to sequence the entire human genome. The information derived from this project will have profound implications for basic biology and clinical medicine alike.

Base Sequence↗
PubMed1987

Topical arachidonic acid: a model for screening anti-inflammatory agents.

Products of arachidonic acid metabolism, prostaglandins and leukotrienes, play an important role in ocular inflammation. In this study, we investigated the efficacies of the cyclo-oxygenase inhibitors (aspirin, indomethacin, and piroxicam) and the lipoxygenase inhibitors (N-hydroxy-arachidonamide (AH) and phenidone) in reducing ocular inflammation induced by arachidonic acid. Administering arachidonic acid topically (0.50% for rabbits and 0.25% for humans) produced a simple model for evaluating the effects of inhibitors on prostaglandins. In rabbits, aspirin, piroxicam and indomethacin all blocked lid closure and chemosis significantly. In humans, aspirin and indomethacin significantly blocked arachidonic acid-induced conjunctival injection. Neither AH nor phenidone blocked any of the signs of ocular inflammation in rabbits or humans. Further testing of phenidone in the presence of the calcium ionophore, ionomycin, also proved negative. Species specificity in arachidonic acid metabolism may account for the different results in humans and rabbits. This model may be a useful tool for comparing the relative efficacies of topical cyclo-oxygenase inhibitors in treating ocular problems.

Administration, Topical↗
PubMed1987

Use of plasma segments for estimating factor VIII activity in pools of fresh frozen plasma.

This study describes a procedure for estimating the factor VIII activity of pools of fresh frozen plasma destined for fractionation into factor VIII concentrates. This information is useful for estimating overall yields. We compared the factor VIII activity of plasma packs and the attached segments shortly after the production of fresh frozen plasmas, during storage at -30 degrees C for up to 4 weeks, after shipping at -20 degrees C to the fractionation site, after storage at -30 degrees C at the fractionation site, and after cryoprecipitation. The factor VIII activity of the segments and the plasma packs were indistinguishable at all stages except after cryoprecipitation. Our results suggest that, prior to the cryoprecipitation stage, a pool of a representative number of plasma segments can be used to determine the factor VIII activity of the plasma pool to be fractionated.

Blood Preservation↗