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Biomedical subjects

W L Smith

Publications and source records attributed to W L Smith.

At least 217 records · Page 12Linked to original sources
PubMed1990

Structure-function relationships in sheep, mouse, and human prostaglandin endoperoxide G/H synthases.

Our studies are designed to determine which amino acid residues are involved in catalyzing the cyclooxygenase and hydroperoxidase activities of prostaglandin endoperoxide (PGG/H) synthase. We have deduced from complementary (c)DNAs the amino acid sequences of the sheep and mouse PGG/H synthases, and a portion of the human PGG/H synthase. These enzymes have amino acid sequences which are about 90% identical. Sequence similarities with putative heme binding regions of myeloperoxidase and thyroid peroxidase suggest that the sequence TI(L)WLREHNRV of PGG/H synthase contains the histidine (His309) which is the proximal heme ligand; the distal heme ligand may be His226 which is found in the sequence 222-KALGH-226. Using site-directed mutagenesis, we have replaced Ser530, the serine residue which is acetylated by aspirin, with Ala530 and with Asn530; the Ala530 mutant has both cyclooxygenase and hydroperoxidase activity, while the Asn530 mutant lacks cyclooxygenase activity but retains hydroperoxidase activity. These results establish that the hydroxyl group of Ser530 is not essential for catalysis or substrate binding and suggest that a bulky group at position 530, such as that introduced by aspirin acetylation, prevents arachidonate binding to the cyclooxygenase active site. Finally, we have found that tetranitromethane causes irreversible inactivation of cyclooxygenase activity and that the enzyme is protected from inactivation when ibuprofen is included in the reaction mixture. These results suggest that there is an essential tyrosine at the active site of PGG/H synthase.

Amino Acid Sequence↗
PubMed1990

Molecular basis for the inhibition of prostanoid biosynthesis by nonsteroidal anti-inflammatory agents.

Many nonsteroidal anti-inflammatory drugs exert their effects by inhibiting the synthesis of prostanoids. More specifically, these agents block the synthesis of prostaglandin endoperoxide G2 from arachidonic acid by competing with arachidonate for binding to the cyclooxygenase active site of prostaglandin endoperoxide synthase. Studies of the molecular biology of prostaglandin endoperoxide synthase indicate that there is a single gene for the enzyme. Thus, tissue-specific effects of nonsteroidal anti-inflammatory drugs probably result from differences in drug distribution and/or metabolism and not from the existence of tissue-specific prostaglandin endoperoxide synthase isozymes. Aspirin causes inactivation of prostaglandin endoperoxide synthase by first binding to the cyclooxygenase active site and then acetylating the protein at Ser530. Although the cyclooxygenase activity is inactivated, the hydroperoxidase activity of prostaglandin endoperoxide synthase is unaltered by Aspirin or other nonsteroidal anti-inflammatory drugs. Replacement of Ser530 of the native enzyme with an alanine residue by site-directed mutagenesis yields a prostaglandin endoperoxide synthase with unaltered catalytic and substrate binding activities. Thus, the hydroxyl group of Ser530 is not essential for enzyme activity. Instead, it appears likely that acetylation of prostaglandin endoperoxide synthase by Aspirin simply places a bulky acetyl group at or near the cyclooxygenase active site, thereby interfering with arachidonic acid binding.

Acetylation↗
PubMed1989

The biosynthesis and actions of prostaglandins in the renal collecting tubule and thick ascending limb.

PGE2 formed by renal collecting tubules is an important factor in regulating NaCl and water reabsorption in the collecting tubule and medullary thick ascending limb. PGE2 appears to act, depending on its ambient concentration, via several different receptors present in these renal epithelia to modulate cAMP turnover in both positive and negative directions. These putative PGE receptors form a family of receptors, all coupled to G proteins, and this family of PGE receptors is homologous to the adrenergic receptor family.

Animals↗
PubMed1989

Cross-institutional stability of behavioral criteria desirable for success in radiology residency.

Certain dimensions of job performance are critical to radiology residents, and several of these dimensions are noncognitive in nature (eg, interpersonal skills, conscientiousness, recognition of limits). Our initial study examined these factors in only one residency program, so the general nature of these dimensions must be documented. The current study was a cross institutional analysis involving 31 faculty radiologists at three separate academic institutions (82% of total faculty) who participated in a critical incident interview to obtain data on important resident behaviors and attitudes. The resultant 172 incidents were sorted by two physicians into the six categories (knowledge, technical skills, attitudes toward self and [both recognitions of limits and confidence in abilities], conscientiousness, curiosity, and interpersonal skills); inter-rater reliability was 92%, kappa = .89. A Chi square analysis revealed similar distributions of incidents across categories (x2 12 = 17.22) among the three institutions, supporting the general reliability of these dimensions across the institutions studied. Further, the distributions of these incidents demonstrated that the noncognitive dimensions again were given considerable importance by faculty radiologists. For example, more than 40% of the critical incidents pertained to the conscientiousness dimension. These findings documented the generalization of these behavioral dimensions across several sites and support their importance in selection and evaluation of residents.

Attitude of Health Personnel↗
PubMed1989

The antiemetic profile of zacopride.

The antiemetic activity of zacopride against a variety of emetogenic agents has been determined in dogs. Zacopride was highly effective in inhibiting emesis due to a wide range of cancer chemotherapeutic agents, particularly cisplatin. It was well absorbed orally since the dose of zacopride required to inhibit cisplatin-induced emesis in dogs by 90% was 28 micrograms kg-1 both by i.v. and p.o. routes. Further, zacopride (1 mg kg-1 p.o.), administered after the onset of cisplatin-induced emesis, reduced the number of subsequent emetic episodes by 91%. Zacopride at 0.1, 1, or 3.16 mg kg-1 p.o. or i.v., reduced the number of emetic episodes due to dacarbazine, mechlorethamine, adriamycin, actinomycin D, or peptide YY by 100, 100, 86, 96 and 79%, respectively. However, zacopride was not effective in inhibiting emesis due to either apomorphine, copper sulphate, protoveratrine A, histamine, or pilocarpine. No adverse effects attributed to zacopride were observed. Zacopride is thus a unique and potent antiemetic agent as it selectively inhibits the emetic response to cancer chemotherapy agents and peptide YY.

Animals↗
PubMed1989

Patient expectations of radiology in noninteractive encounters.

Open-ended interviews with 107 patients documented specific patient expectations of radiologic procedures during which there was no direct radiologist-patient interaction. Patient expectations could be classified into those related to the facility and those related to interactions with radiology staff. Among facility-related expectations, waiting time far outweighed all other concerns. Interpersonal skills were the predominant expectation of radiology staff. The role of the radiologist in fulfilling patient expectations was less clear. Only 10% of unprompted patients cited the radiologist as a factor in their expectations. When patients were specifically prompted to discuss the radiologist's role, communication skills, accuracy of interpretation, and interpersonal skills were the predominant concerns.

Attitude↗
PubMed1989

Head injury in child abuse: evaluation with MR imaging.

To evaluate the usefulness of magnetic resonance (MR) imaging in the diagnosis of head injury in child abuse, the authors compared the findings at head MR imaging and computed tomography (CT) in 19 abused children. Subdural hematomas (15 cases), cortical contusions (six cases), and shearing injuries (five cases) were demonstrated to particular advantage with MR imaging. CT remained superior in the detection of subarachnoid hemorrhage. MR imaging appears to be valuable in the assessment of patients with suspected intracranial injury due to child abuse.

Brain Concussion↗
PubMed1989

Regulation of cAMP metabolism by PGE2 in cortical and medullary thick ascending limb of Henle's loop.

We have examined the regulation by prostaglandin E2 (PGE2) of hormone-induced adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in cells isolated by immunodissection from both the medullary and cortical thick ascending limb of Henle's loop of rabbit kidney. At concentrations greater than 10(-8) M, PGE2, but not sulprostone (16-phenoxy-17,18,19,20-tetranor-PGE2 methylsulfonilamide), caused cAMP accumulation in both cortical and medullary thick limb cells. However, at concentrations of less than or equal to 10(-8) M, both PGE2 and sulprostone inhibited arginine vasopressin (AVP)-, calcitonin-, and glucagon-induced cAMP accumulation in medullary thick ascending limb (mTAL) cells. In cortical thick limb (cTAL) cells, sulprostone also inhibited AVP-, calcitonin-, and parathyroid hormone (PTH)-induced cAMP accumulation. The inhibitory effects of PGE2 and of sulprostone were blocked by pretreatment of mTAL and cTAL cells with pertussis toxin. Membranes prepared from mTAL cells exhibited a [3H]PGE2 binding activity that was stimulated on addition of the stable guanosine 5'-triphosphate (GTP) analogue, 5'-guanosine gamma-thiotriphosphate (GTP gamma S); moreover, sulprostone inhibited [3H]PGE2 binding. Our results suggest that PGE2 can function via a prostaglandin E receptor linked to a guanine nucleotide regulatory protein, Gi, to attenuate hormone-induced cAMP formation in both mTAL and cTAL cells of rabbit kidney.

Animals↗
PubMed1989

Effect of intravenously administered lipoxygenase metabolites on rat tracheal mucous gel layer thickness.

The effect of intravenous injections of 5-, 12- and 15-hydroxyeicosatetraenoic acids (HETE), leukotrienes D4 and E4 (LTD4, LTE4) on tracheal mucous gel layer (TMGL) thickness was assessed in rats. When administered in doses ranging from 0.03 pg to 33 ng per rat, the lipoxygenase metabolites produced significant increases in TMGL thickness. The order of potency of the metabolites was 15-HETE greater than 12-HETE greater than or equal to 5-HETE greater than LTD4 greater than or equal to LTE4. Imidazole (31.6 mg/kg), intravenously, significantly decreased this response. These findings suggest that the mono-HETEs, especially 15-HETE, may be important modulators of airway mucus in the rat.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1989

Rapid induction of prostaglandin endoperoxide synthase in rat preovulatory follicles by luteinizing hormone and cAMP is blocked by inhibitors of transcription and translation.

Prostaglandin endoperoxide synthase (PGS) catalyzes the rate-limiting step in the synthesis of prostaglandins E and F2 alpha that are obligatory for ovulation. To understand the molecular mechanisms by which LH regulates the induction of PGS in rat preovulatory (PO) follicles, we established an in vitro system which mimics in vivo induction of the enzyme. We show that the rapid increase in PGS enzyme: 1) is stimulated by LH, FSH, and forskolin (cAMP) in a time- and dose-dependent manner that is distinct from changes in steroidogenic enzymes analyzed in the same follicles; 2) is unaltered by end products (PGE and PGF2 alpha) of the reaction or inhibitors (indomethacin) of enzyme activity; 3) is blocked by inhibitors of transcription (alpha-amanitin) and translation (cycloheximide) at a step distal to production of cAMP and activation of A-kinase. Analyses of PGS mRNA by Northern blots using a mouse PGS cDNA probe revealed a PGS transcript of 2.8 kilobases that was present but in low abundance in PO follicles and decreased rapidly (1-4 h) as a consequence of LH/human CG stimulation. This hormone-induced decrease in PGS mRNA appeared to be transient because PGS transcripts were present in corpora lutea at a level similar to that in PO follicles. These results raise the possibility that the marked increase in PGS enzyme in granulosa cells of PO follicles that occurs as a consequence of the LH/human CG surge may not involve a cAMP regulated increase in transcription of the PGS gene itself. Or, if increased transcription of PGS mRNA does occur, it is rapid and coupled with cotranslational degradation of the mRNA. Alternatively, transcriptional (alpha-amanitin-sensitive) regulation of a separate gene may be obligatory for increased translation of PGS mRNA or posttranslational modification (stabilization?) of the enzyme. In summary, the LH-stimulated appearance of PGS in granulosa cells of PO follicles before ovulation is mediated by cAMP in a complex manner involving transcriptional regulation (PGS gene?) and translational control of PGS mRNA. The transient appearance of the PGS enzyme represents a unique pattern of response by granulosa cells of PO follicles to LH/cAMP and thereby may involve novel intracellular factors and regulatory processes.

Animals↗
PubMed1989

MR imaging of the craniovertebral junction, cranium, and brain in children with achondroplasia.

MR imaging of the craniovertebral junction, cranium, and brain was performed in 10 patients (aged 3 months to 16 years) with achondroplasia. All patients had narrowing of the subarachnoid space at the level of the foramen magnum and five had compressive deformities of the cervicomedullary junction. Apparent upward displacement of the brainstem and a relatively vertical course of the optic nerve were seen in all patients. Dilated lateral and third ventricles were seen in five patients and bifrontal widening of the subarachnoid space was evident in four. Skull asymmetry was seen in two patients and an empty sella (confirmed by metrizamide cisternography) was present in one individual. In one patient, foci of abnormal signal intensity were seen in the cervicomedullary region. Our experience indicates that MR imaging is useful in delineating the many abnormalities of the cranial, cerebral, and cervicomedullary junction present in children with achondroplasia.

Achondroplasia↗
PubMed1989

Preferential decay of passively acquired immunoglobulins recognizing shared gram-negative core antigens in neonatal swine.

Serum immunoglobulins of the IgG isotype recognizing common gram-negative cell core epitopes were serially measured by use of a direct ELISA on blood obtained from 10 neonatal swine. An R-mutant Escherichia coli (strain J5) was used as a plate antigen. Total serum IgG was measured by use of radial immunodiffusion. Half-lives of core antigen-specific IgG (6.81 days) and total serum IgG (14.85 days) were dramatically different (P less than 0.01).

Animals↗