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Biomedical subjects

R D Smith

Publications and source records attributed to R D Smith.

At least 217 records · Page 12Linked to original sources
PubMed1994

EXP597, a nonpeptide angiotensin II receptor antagonist with high affinities for the angiotensin AT1 and AT2 receptor subtypes.

AT1 and AT2 are the two major receptor subtypes for angiotensin II that have been pharmacologically defined by using the selective ligands losartan and PD123177, respectively. EXP597 (4-[(5-(2-benzoyl)benzyloxycarbonyl-4-ethyl-2-n-propylimidazole-1- yl)methyl]-3-fluoro-2'-isoamyloxycarbonylaminosulfonyl-[1,1']-biph enyl, potassium salt) is a nonpeptide angiotensin II receptor ligand which in the rat adrenal exhibits binding affinities (IC50) of 0.5 and 0.7 nM for angiotensin AT1 and AT2 receptor subtypes, respectively. Further, EXP597 is an insurmountable angiotensin II receptor antagonist in the isolated rabbit aorta and lowers blood pressure in renal hypertensive rats with i.v. and p.o. ED30 values of 0.05 and 0.9 mg/kg, respectively.

Administration, Oral↗
PubMed1994

Protein kinase C rapidly up-regulates the number of AT1 angiotensin receptors on cultured rat intestinal epithelial (RIE-1) cells.

Addition of 12-O-tetradecanoylphorbol-13-acetate to RIE-1 rat intestinal epithelial cells stimulated a rapid (mean 3-fold) increase in the subsequent binding of 125I-labelled angiotensin II which was reversed or prevented when cellular protein kinase C was depleted. The increased binding was due, in part, to an up-regulation in the number of AT1 angiotensin receptors on RIE-1 cells, without any significant change in their binding affinity. Since this rapid up-regulation was independent of receptor synthesis, it may result from an increased availability (to extracellular ligand) of performed, but previously 'cryptic', AT1 angiotensin receptors.

Animals↗
PubMed1994

Charge-state shifting of individual multiply-charged ions of bovine albumin dimer and molecular weight determination using an individual-ion approach.

Ion-molecule reactions of individual multiply-protonated ions of bovine albumin dimer, formed from electrospray ionization, have been studied using a Fourier transform ion cyclotron resonance mass spectrometer. Upon reaction of ammonia with a group of individual ions, charge-state shifting was observed due to proton transfer. Repeated additions of ammonia during remeasurements of the same ion population were observed to induce multiple-step charge-state shifts. Charge-state-dependent reactivity, as well as nonstatistical behavior in reactivity, was observed due to the small ion population. The molecular weights of individual ions whose charge state shifted during reaction were determined with an accuracy of 67 ppm, the first example of using an individual-ion approach to the determination of molecular weight for a large biopolymer. The molecular weight distribution of a group of ions can be determined with a precision related to the number of ions examined and the weight heterogeneity of the sample. We obtained the molecular weight for eight individual ions from which a molecular weight of 133,320 +/- 210 Da was calculated for bovine albumin dimer.

Animals↗
PubMed1994

Sheathless capillary electrophoresis-electrospray ionization mass spectrometry using 10 mu m I.D. capillaries: analyses of tryptic digests of cytochrome c.

The analyses of tryptic digest of proteins present a difficult challenge to the analytical chemist due to the wide range of molecular masses and hydrophobicities of the peptides produced. In this study, we demonstrate the separation of tryptic digests of bovine, Candida krusei and equine cytochrome c using a new electrospray ionization (ESI) interface for CE-MS that does not require additional sheath make-up fluid or mechanical assistance to aid the ESI process. The utility of this new CE-ESI-MS interface is demonstrated using a 10 microm I.D. CE capillary where the injected sample amounts are in the 30 femtomole (of protein) region. The CE electroosmotic flow rates when aminopropylamine treated capillaries are utilized are in the 10 nl/min region for a relatively conductive buffer system (0.01 M ammonium acetate-acetic acid buffer system, pH 4.4 and a 300 V/cm field strength).

Amino Acid Sequence↗
PubMed1994

Charge state specific facile gas-phase cleavage of Asp 75-Met 76 peptide bond in the alpha-chain of human apohemoglobin probed by electrospray ionization mass spectrometry.

Herein, we present the first example of charge state specific facile gas-phase cleavage of an aspartic acid-methionine peptide linkage. This cleavage (Asp 75-Met 76) was observed in the alpha-chain of human adult hemoglobin (Hb) and was probed by electrospray ionization mass spectrometry. This specific conformational and/or charge density dependent dissociation was observed primarily in the [M + 11H]11+ and [M + 12H]12+ species. A mechanism involving an intramolecular proton transfer from the protonated carboxyl side chain of Asp 75 to the neighboring Met 76 residue yielding an anhydride moiety at the C-terminal of the Asp 75 is proposed. Dramatic differences in dissociation of [M + 13H]13+ and [M + 14H]14+ species were observed.

Amino Acid Sequence↗
PubMed1994

Comparison of the responses of three rat intestinal epithelial cell lines to angiotensin II.

Like RIE-1 cells, two of the IEC series of rat intestinal epithelial cell lines were found to express functional angiotensin receptors. As in RIE-1 cells, treatment of IEC-6 or IEC-18 cells with angiotensin II (AII) activated phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis although (in contrast to RIE-1 cells) the magnitude of AII-induced PIP2 hydrolysis was small and not associated with a mitogenic response in either IEC cell line. In terms of their other functional responses to AII (activation of protein kinase C (PKC) and a small elevation of cyclic AMP), IEC-6 cells are otherwise similar to RIE-1 cells whereas IEC-18 cells exhibit some phenotypic differences to the other two cell types. Thus, whereas IEC-6 and RIE-1 cells each express the AT1 subtype of angiotensin receptor, the higher affinity receptors on IEC-18 cells are 'atypical', being insensitive to both AT1- and AT2-specific angiotensin receptor antagonists. Furthermore, in contrast to its effects in IEC-6 and RIE-1 cells, AII neither activates PKC nor modulates cyclic AMP levels in IEC-18 cells. Whereas IEC-18 cells express the myristoylated alanine-rich C-kinase substrate (MARCKS), immunoreactive MARCKS was not detected in IEC-6 or RIE-1 cells.

Angiotensin II↗
PubMed1994

The anti-proliferative action of transforming growth factor-beta 1 on a rat intestinal epithelial cell line (RIE-1) is dependent on cell population density and culture passage number.

1. The proliferation of RIE-1 rat intestinal epithelial cells was potently but reversibly inhibited by transforming growth factor-beta 1 (TGF-beta 1). In early-passage cultures, complete growth arrest was observed when sparse cultures were treated with TGF-beta 1 (1 ng/ml). 2. However, increasing the initial cell culture density resulted in decreased TGF-beta 1-mediated inhibition of cell proliferation. 3. Independent of this population density effect, RIE-1 cells also exhibit a marked phenotypic transition around passage-8 to -10, such that later-passage cells were less responsive to growth inhibition by TGF-beta 1.

Animals↗
PubMed1994

Effects of recombinant human erythropoietin on renal function in chronic renal failure predialysis patients.

A study was undertaken to ascertain the effects of recombinant human erythropoietin (r-HuEPO) on renal function in chronic renal failure predialysis patients. The effect of improvement of anemia by r-HuEPO on the rate of decline in renal function in predialysis patients has not been previously studied prospectively in a large number of patients using reliable measures of glomerular filtration rate (GFR). To investigate the efficacy, safety, and impact of r-HuEPO therapy in chronic renal insufficiency patients, a 48-week, randomized, open-label, multicenter study was initiated in 83 anemic, predialysis (serum creatinine 3 to 8 mg/dL) patients. Serial GFRs were measured using 125I-iothalamate clearance. Forty patients were randomized to the untreated arm and 43 patients to the treatment arm (50 U/kg r-HuEPO subcutaneously three times weekly). Baseline characteristics were comparable for the r-HuEPO-treated and untreated groups. During this 48-week study, GFR, mean arterial blood pressure, and daily protein intake were not significantly different between the two groups. There was a statistically significant increase in hematocrit for the r-HuEPO-treated group that was not associated with acceleration of deterioration in residual renal function. This was demonstrated by the lack of a significant (P = 0.376) between-group difference in mean change in GFR from baseline to last available value for the r-HuEPO-treated (-2.1 +/- 3.2 mL/min) and untreated (-2.8 +/- 3.5 mL/min) groups. This study concludes that r-HuEPO therapy improves anemia in predialysis patients and does not accelerate the rate of progression to end-stage renal disease.

Adult↗
PubMed1994

Angiotensin II receptor subtypes: selective antagonists and functional correlates.

Angiotensin II (Ang II) receptor heterogeneity is currently defined by the new subtype-selective agents, losartan (AT1) and PD123177 (AT2). Although both subtypes have been cloned and sequenced, only the AT1 receptor has been shown to have an important physiological or pathophysiological role. AT1 and AT2 receptors are found in both normal and failing cardiac tissue. They are found on myocytes, endothelial cells, fibroblasts, coronary arterial smooth muscle cells, and peripheral sympathetic nerves. The AT1 receptors mediate virtually all of the effects of Ang II in myocytes even though cardiac tissue may contain over 50% AT2 sites. In endothelial cells, functional responses are predominately AT1. In fibroblasts, preliminary data suggest that AT2 receptors may be involved in collagen synthesis. In isolated tissue, Ang II has a limited positive inotropic effect in atrial, but not in ventricular tissue, which is blocked by losartan. Ang II may also have a tonic effect on coronary artery resistance as angiotensin inhibitors can increase coronary flow. Both ACE (Ang II synthesis) inhibitors and Ang II receptor antagonists produce beneficial effects in experimental models of heart failure, suggesting Ang II is an important mediator of heart failure. Because ACE inhibitors also potentiate bradykinin and are non-specific inhibitors of Ang II synthesis (availability of Ang II to both receptor subtypes) some differences can be anticipated. At the present time, however, the beneficial role of bradykinin is controversial and the predominant functional Ang II receptor in the heart and other tissues is the AT1 subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1994

Keeping the customer satisfied: issues in the interpretation and use of patient satisfaction surveys.

Patient satisfaction and customer focus are increasingly important objectives set for health services. The patient satisfaction survey is becoming the main method of assessing this aspect of health care. In competitive environments, those institutions that show that they respond to consumers' needs are in a better position to attract funding. The use of patient satisfaction surveys in quality assurance-type activities is also increasing. In these contexts, however, the way in which patient satisfaction surveys should be interpreted and used to maximise the satisfaction of patients has received little critical attention. Problems in interpreting the results of satisfaction surveys arise from the weak conceptual foundation of patient satisfaction, which has been well documented in the literature. The objective of this paper is to show that using current formulations of patient satisfaction surveys in quality assurance-type activities and competitive environments may not lead to the maximisation of patients' satisfaction with health services. If the satisfaction of patients is to be maximised then it is necessary to extend the current conceptual basis of patient satisfaction to recognise explicitly the decision-making contexts in which the results will be used. This paper identifies the manner by which this extension should occur by considering some of the problems and pitfalls of interpreting and using the results of surveys to maximise patients' satisfaction.

Decision Making, Organizational↗
PubMed1994

Human angiotensin receptor subtypes.

The rapid expansion of our knowledge of angiotensin receptors has been led by the development of subtype-specific angiotensin II receptor antagonists and by the cloning and sequencing of the AT1 receptor in angiotensin II. Although some actions of angiotensin II have been attributed to AT2 subtype receptors, the importance of these binding sites remains elusive. Nonpeptide, AT1-selective antagonists, such as losartan, block virtually all of the well-known effects of angiotensin II in mammalian cells. The effects of losartan are now being confirmed by the rapidly developing class of nonpeptide, AT1-selective angiotensin II receptor antagonists. In rodents, subtypes of the AT1 receptor have been cloned and designated AT1A and AT1B, but they have not been functionally distinguished. Such isoforms have not been identified for human AT1 receptors. Importantly, it now appears that the AT2 receptor has been cloned. The angiotensin receptors undergoing intense study are those in fetal tissue, brain, endothelial cells, and fibroblasts. Angiotensin II-induced growth and cardiovascular hypertrophy are the focus of broad-based research efforts. The clinical relevance of angiotensin II receptor subtypes is unknown, but there is growing evidence that AT1-selective agents are effective inhibitors of the angiotensin system in humans.

Angiotensin I↗
PubMed1994

A new class of therapeutic agents: the angiotensin II receptor antagonists.

Angiotensin II (Ang II) is the primary mediator of the renin-angiotensin system (RAS). Inappropriate control of the RAS is critically involved in the development and maintenance of hypertension and congestive heart failure. The actions of Ang II are thought to be mediated by specific surface receptors on the various target organs. At present, two receptors for Ang II have been firmly established in mammals, including man. According to current nomenclature, losartan represents the prototype antagonist of the Ang II type 1 (AT1) receptor and does not possess significant affinity for the so-called AT2 receptor. Losartan is the first of a new class of orally active, nonpeptide Ang II receptor antagonists able to very specifically and selectively inhibit the RAS while lacking the agonistic effects of the peptide receptor antagonists, e.g. sarlasin, or the bradykinin potentiating effects of the angiotensin converting enzyme (ACE) inhibitors. Virtually all of the known actions of Ang II, e.g. those defined by Ang II itself, saralasin, ACE or renin-inhibitors are blocked by losartan, emphasizing the major role of this distinct Ang II receptor subtype in mediating the responses of Ang II. The functional correlate of the AT2 receptor remains poorly understood. In several models of experimental and genetic hypertension, AT1 receptor antagonists are effective antihypertensive agents with similar efficacy to that of ACE and renin-inhibitors. In animal models of renal disease, AT1 receptor antagonists significantly decrease proteinuria, protect against diabetic glomerulopathy and increase survival in stroke-prone spontaneously hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin Receptor Antagonists↗
PubMed1994

A prospective study of adolescents who choose among levonorgestrel implant (Norplant), medroxyprogesterone acetate (Depo-Provera), or the combined oral contraceptive pill as contraception.

OBJECTIVES: Levonorgestrel implants (Norplant) and medroxyprogesterone acetate injections (Depo-Provera) represent additional contraception options for adolescents. The purpose of this study was to examine prospectively clinical profiles among adolescents who chose one of the two long-term contraceptives compared with profiles among those who chose the combined oral contraceptive pill (OCP). METHODS: Girls who needed contraception and did not require confidentiality were presented with a contraceptive menu consisting of Norplant (n = 58), Depo-Provera (n = 66), or OCP (n = 75). At baseline and follow-up visits over 6 months, patients were interviewed regarding gynecologic history, side effect symptoms, and satisfaction. The average age of subjects was 15.5 years (range 11 to 20 years); 66% were African-American and 34% white. RESULTS: Significantly more teens who chose Depo-Provera (73%) reported having used some method of birth control previously than those selecting either Norplant (30%) or OCP (26%). Adolescents who chose either Norplant (34%) or Depo-Provera (43%) were significantly more likely to have been pregnant previously than those choosing OCP (12%). Those selecting Depo-Provera were significantly more likely to report a history of genital infection with Chlamydia trachomatis (42%) than those in the other two contraceptive groups (22%). Prevalences of reported recent depression and fatigue before initiation of treatment were high, exceeding 35% across the three groups. A total of 105 and 40 adolescents were assessed at 3 and 6 months, respectively. At follow-up, more than 80% of OCP users maintained regular menstrual cycles, whereas over 80% of those choosing Norplant or Depo-Provera had disrupted cycles. Complaints of nausea and dizziness among Norplant users and fatigue among Depo-Provera and OCP users increased significantly between the baseline and follow-up visits. Reports of local reactions to the Norplant device were common but not clinically significant. Blood pressure readings, facial acne, and body mass index did not change over time in any treatment group. Subjects in the Norplant and Depo-Provera groups appreciated freedom from daily compliance to maintain contraceptive effectiveness and the "hidden" nature of the method. Appointment compliance at the end of 6 months was 78% for Depo-Provera, 40% for Norplant, and 46% for OCP. CONCLUSIONS: The implant and injection forms of contraception appear to be especially popular among girls with previous pregnancies or birth control use. The common occurrences of medical symptoms and sexually transmitted diseases before initiation of therapy underscore the importance of baseline evaluation. Norplant users may be warned about nausea and dizziness as well as minor local symptoms around the insertion site and unpredictable uterine bleeding patterns. Adolescent patients choosing Depo-Provera may expect amenorrhea by the end of 6 months of therapy along with possible fatigue. Early intervention may be needed with adolescents who choose Norplant or OCP to encourage better compliance with follow-up appointments.

Adolescent↗
PubMed1994

Phorbol ester-, but not ligand-mediated activation of protein kinase C increases angiotensin binding to rat intestinal epithelial (RIE-1) cells.

Whereas direct activation of protein kinase C (PKC) by the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) increased the subsequent binding of 125I-labelled angiotensin II (125I-AII; 0.5 nM) to RIE-1 cells, ligand-mediated activation of the kinase via angiotensin II (AII), which activates the phosphoinositide (PI) pathway in these cells, had no effect. The apparent inability of AII to increase 125I-AII binding is unlikely to result from simultaneous, but opposing actions of AII on angiotensin receptor number and affinity since the peptide also had no effect on the saturation binding of 125I-AII (10 nM) to the cells. Since 125I-AII binding was unaffected both by AII pretreatment in PKC-depleted cells, and by the calcium ionophore, ionomycin, in PKC-replete cells, an attenuating action of AII (opposing any PKC-mediated increase) on 125I-AII binding mediated via the calcium limb of the PI pathway is also unlikely. Instead, the contrasting effects of AII and TPA on 125I-AII binding to RIE-1 cells appear to relate to the degree of PKC activation elicited by each agent.

Angiotensin II↗
PubMed1994

Regulation of growth factor receptors on rat intestinal epithelial (RIE-1) cells by protein kinase C.

The regulation of growth factor receptors by protein kinase C was investigated in rat intestinal epithelial (RIE-1) cells. Short-term treatment of the cells with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, was employed to activate the kinase and longer-term exposure to the agent was used to assess the effects of protein kinase C depletion. Phorbol ester concentrations as low as 30 nM were found to down-regulate immunoreactive protein kinase C over 6 h, which correlated with the rapid loss of functional kinase activity. Whereas protein kinase C reduced the binding of 125I-labelled EGF, it increased the binding of 125I-labelled angiotensin II to RIE-1 cells. However, the kinase simultaneously inhibited the activation by angiotensin receptors of phosphatidylinositol 4,5 bisphosphate hydrolysis.

Angiotensin II↗
PubMed1994

Characterisation of AT1 angiotensin receptors on cultured rat intestinal epithelial (RIE-1) cells.

The relative binding affinities of non-peptide antagonists, and the sensitivity of 125I-angiotensin II (125I-AII) binding to the reducing agent, dithiothreitol, indicated the presence of AT1 angiotensin receptors on RIE-1 rat intestinal epithelial cells. Consistent with this finding, AT1 angiotensin receptor mRNA was detected in RIE-1 cells using Northern blotting, whereas no mas transcripts (which also encode an angiotensin receptor) were detectable using a RNAse protection assay. At 37 degrees C, 125I-AII rapidly bound to RIE-1 cells and internalised into an acid-inaccessible compartment, which resulted in the depletion of 125I-AII from the binding medium. Following overnight incubation of RIE-1 cells with 125I-AII at 4 degrees C, the majority of bound ligand was also, unexpectedly, found to be inaccessible to subsequent acid elution. After warming these cultures to 37 degrees C, acid-inaccessible 125I-radioactivity rapidly disappeared from the cells, and 125I-labelled degradation products accumulated in the medium. Scatchard analysis of the concentration-dependent binding of 125I-AII solely to the acid-accessible sites on RIE-1 cells revealed little difference to the KD value obtained from total 125I-AII binding (to both acid-accessible and -inaccessible sites), but only approximately 15% of the number of sites.

Angiotensin II↗