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Biomedical subjects

M Keen

Publications and source records attributed to M Keen.

At least 37 records · Page 2Linked to original sources
PubMed1994

Desensitization of adenylate cyclase responses following exposure to IP prostanoid receptor agonists. Homologous and heterologous desensitization exhibit the same time course.

Pretreatment of NG108-15 cells with 0.03-25 microM prostaglandin E1 (PGE1) produced decreases in the maximal stimulation of adenylate cyclase activity produced by iloprost, N-ethylcarboxamidoadenosine and sodium fluoride. The rate of desensitization to all three agents was dependent on the concentration of PGE1 used, but at each concentration of PGE1 the rate of loss of responsiveness to each agent was the same, suggesting that the decreases in responsiveness may be mediated by a single process. Functional desensitization was accompanied by a decrease in the specific binding of [3H]iloprost, consistent with a 75-80% decrease in IP receptor number, with no change in the coupling of the remaining IP receptors to G protein. At each concentration of PGE1 used, the times taken for half maximal decreases in receptor number and functional responsiveness were similar, suggesting that IP receptor down-regulation is a relatively early event in desensitization. IP receptor down-regulation could be inhibited partially by 100 microM chloroquine, suggesting that lysosomal breakdown of receptors may be occurring.

Adenylyl Cyclases↗
PubMed1994

Botulinum toxin A for hyperkinetic facial lines: results of a double-blind, placebo-controlled study.

Previous work on patients with muscular dystonia has shown that small intramuscular doses of botulinum toxin A eliminated hyperkinetic facial lines for approximately 6 months. The purpose of this study was to determine the efficacy of botulinum toxin A injections in eliminating facial wrinkles in aesthetic surgery patients who do not have muscular dystonia. Eleven healthy subjects were studied in a double-blind fashion. On both sides of the face, 0.2 cc of either normal saline or botulinum toxin A was injected into the forehead or into the periorbital wrinkles (crow's feet). Documentation of results was made by photographs taken of the patients during repose and during facial animation before and after injection. Assessment of facial wrinkles was done from a grading system in which the patient and the facial plastic surgeon were asked to judge the severity of the wrinkles on a scale from 0 to 3, with 0 reflecting no facial wrinkles and 3 reflecting severe facial wrinkling. Nine of 11 subjects injected with botulinum toxin A noted a significant improvement in the severity of their facial wrinkles in comparison with the side of the face injected with saline, with a rating improvement of 2 points. Two of 11 subjects noted a moderate improvement, with a rating improvement of 1 point. No patient injected with saline reported an improvement in the severity of the facial wrinkles on the control side. There were no serious complications. Botulinum toxin A is an efficacious method of nonsurgically eliminating facial wrinkles and may play a role in the cosmetic enhancement of the aging face.

Adult↗
PubMed1993

The measured creatinine generation rate in CAPD suggests only 78% of prescribed dialysis is delivered.

The creatinine generation was measured (GCr) in 132 continuous ambulatory peritoneal dialysis (CAPD) patients from the product of total daily peritoneal plus renal creatinine clearance and plasma creatinine (CpCr) plus the product of estimated gut clearance of 0.036 L/kg/day and CpCr. The creatinine generation was also predicted (PGCr) from gender, age, and weight. The mean ratio of MGCr/PGCr was 1.29. Analysis of these data suggests that on average, only 78% of the prescribed dialysis is actually delivered in CAPD patients. Further studies are suggested for the verification of the assumed gut creatinine clearance.

Body Weight↗
PubMed1992

Characterization of the thromboxane receptor mediating prostacyclin release from cultured endothelial cells.

The thromboxane A2 (TXA2) mimetic, 9,11-dideoxy-11,9-epoxymethano-prostaglandin F 2 alpha (U46619), mobilized calcium in the bovine aortic endothelial cell line AG4762 and stimulated release of prostacyclin from these cells. The U46619-stimulated release of prostacyclin could be inhibited by TXA2 antagonists with the order of potency [Is-[1 less than a, 2 less than b(5z), 3 less than b, 4 less than a]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo- [2.2.1]hept-2-yl]-5- heptenoic acid (SQ29548) greater than 4-[2-(4-chlorobenzene-sulphonamido) ethyl]phenylacetic acid (BM13505) greater than 4-[2-(phenylsulphonamido)-ethyl]phenoxyacetic acid (BM13177), which was consistent with release being mediated by a TXA2 (TP) receptor. The TP receptor ligands, [3H]SQ29548 and 9,11-dimethylmethano-16(3-[125I]iodo-4-hydroxyphenyl)-13,14-dih ydr o-13-aza- 15-omega-o-tetranor-thromboxane ([125I]-PTA-OH), both appeared to bind to a homogenous population of sites in AG4762 cell membranes. The affinities of [3H]SQ29548 and [125I]PTA-OH were approximately 10 nM and approximately 0.3 nM, respectively, and the density of sites labelled by either ligand was approximately 25 fmol/mg protein. Under conditions where equilibrium was approached, the specific binding of [3H] SQ29548 or [125I]PTA-OH was displaced by SQ29548, BM13505 and BM13177 with the same order of potency and similar apparent affinities as in the functional assay, suggesting that these binding sites represent bona fide TP receptors.

Bradykinin↗
PubMed1992

Cyclic AMP produces desensitization of prostacyclin and adenosine A2 receptors in hybrid cell lines but does not affect Gs function.

Prostacyclin and adenosine A2 receptors stimulate adenylate cyclase activity in the related somatic hybrid cell lines NG108-15 and NCB20. The role of cAMP in the desensitization of these receptors has been examined. Pretreatment for 17 h with forskolin or 8-bromo-cAMP had the same effect in both cell lines. There was no change in the response to sodium fluoride or forskolin, suggesting that the function of Gs and adenylate cyclase were unaffected by increased levels of cAMP. Receptor responses were affected however; the maximum response to N-ethylcarboxamidoadenosine (an A2 receptor agonist) was reduced by 30-40%, there was a small but consistent shift to the right of the dose-response curve for iloprost (a stable analogue of prostacyclin) and [3H]iloprost binding studies revealed a loss of prostacyclin receptors. However, the loss of receptor responsiveness was much smaller than that which occurs following pretreatment with prostacyclin or adenosine A2 receptor agonists (Keen et al. (1989) Biochem. Pharmacol. 38, 3827-3833; Kelly et al. (1990) Br. J. Pharmacol. 99, 309-316) suggesting that cAMP may not play a major role in agonist mediated desensitization.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Immediate reversible rehabilitation of the paralyzed eyelid.

Skull base surgeons are frequently required to operate in close proximity to the facial nerve. At times, a skull base tumor is resected with the facial nerve grossly infact, only to have the patient awaken with a unilateral facial paresis or paralysis. In the selected cases where the surgeon is certain that the facial nerve has been left intact and return of function is expected, methods are needed to ameliorate the temporary paresis or paralysis of the eyelids. In our institution, eyelid closure has been achieved by placement of a gold weight in the upper eyelid. These weights were placed with the knowledge that they could be removed once facial nerve function returned. We report on 11 such patients who had gold weights placed within 3 weeks of their original intracranial or skull base procedure. All patients were discharged with adequate eyelid closure. Three patients later required lower lid surgery for poor tone or persistence of paralysis. Our experience is reviewed and our recommendations concerning the management of temporary facial paralysis of the eyelids is presented.

Journal Article↗
PubMed1992

Images of nephrology nursing practice: report of a survey.

The results of a survey designed to identify existing images of nephrology nursing practice are reported. The sample included 374 attendees at meetings sponsored by the American Nephrology Nurses' Association (ANNA). Content analysis revealed that the typical nephrology patient is elderly, has a chronic illness and negative affect, is not compliant, and is dependent on others. The typical nephrology nurse-patient interaction emphasizes teaching and support. The most common nursing activities are assessment, teaching, dialysis treatment, and psychological support.

Attitude of Health Personnel↗
PubMed1991

Guanine nucleotide sensitivity of [3H]iloprost binding to prostacyclin receptors.

A component of the displaceable binding of the stable prostacyclin analogue, [3H]iloprost, to membranes from human platelets and the somatic hybrid cell lines NG108-15 and NCB20, was inhibited by guanine nucleotides. The order of potency of a range of nucleotides for this effect was GTP gamma S greater than GppNHp greater than GTP greater than GDP = GMP; ATP, UTP and CTP were ineffective at concentrations up to 1 mM. In the presence of 100 microM GppNHp, iloprost binding curves were displaced to the right of curves obtained in the absence of guanine nucleotide, and their Hill slopes were greater. This was consistent with a conversion of a minor population of high affinity agonist binding sites to lower affinity sites in the presence of guanine nucleotides. These effects of guanine nucleotides on the binding of the agonist ligand [3H]iloprost were consistent with an interaction with a G protein coupled receptor.

Cell Membrane↗
PubMed1991

Cleft lip and palate surgery in La Ceiba, Honduras.

The volume of experience in the surgical repair of cleft lip and palate deformities is limited in many areas of the United States. This deficit in experience exists not only for those in resident training programs but also for those who practice at universities or are in private practice. Physicians are performing too few operations to maintain their surgical skills in cleft lip and palate surgery. This deficit is also encountered by physicians in the major specialties of plastic surgery, oral surgery, and otolaryngology who perform cleft lip and palate surgery. Physicians from the United States can gain surgical experience in other countries through groups like the Medical Group Mission Christian Medical and Dental Society. Surgical experience is available in Central and South America, India, China, and Africa through similar organizations. The complexity of providing service to under-privileged people through organizations such as the Medical Group Mission Christian Medical and Dental Society is described.

Child↗
PubMed1991

Testing models of agonism for G protein-coupled receptors.

Despite much debate as to the validity of different models of agonism, there is apparently very little to choose between them in practice. However, most experiments to test the various models have used classical isolated tissue systems. In these systems, the response that is measured is far removed from receptor activation, and it is likely that the properties of the events at the receptor may be masked by more distal processes. In this article, Mary Keen examines the effects of agonists on responses that follow, very closely, activation of G protein-coupled receptors. The data appear to be inconsistent with any of the current models of agonism.

Adenylyl Cyclase Inhibitors↗
PubMed1991

Octimibate, a potent non-prostanoid inhibitor of platelet aggregation, acts via the prostacyclin receptor.

1. Octimibate, 8-[(1,4,5-triphenyl-1H-imidazol-2-yl)oxy]octanoic acid, is reported to have antithrombotic properties. This is in addition to its antihyperlipidaemic effects which are due to inhibition of acylCoA:cholesterol acyltransferase (ACAT). The aim of this study was to investigate the mechanism of the antithrombotic effect of octimibate, and to determine whether the effects of octimibate are mediated through prostacyclin receptors. 2. In suspensions of washed (plasma-free) human platelets, octimibate is a potent inhibitor of aggregation; its IC50 is approx. 10 nM for inhibition of aggregation stimulated by several different agonists, including U46619 and ADP. The inhibitory effects of octimibate on aggregation are not competitive with the stimulatory agonist; the maximal response is suppressed but there is no obvious shift in potency of the agonist. In platelet-rich plasma, octimibate inhibits agonist-stimulated aggregation with an IC50 of approx. 200 nM. 3. Octimibate also inhibits agonist-stimulated rises in the cytosolic free calcium concentration, [Ca2+]i, in platelets. Both Ca2+ influx and release from intracellular stores are inhibited. The effects of octimibate on aggregation and [Ca2+]i are typical of agents that act via elevation of adenosine 3':5'-cyclic monophosphate (cyclic AMP). Similar effects are seen with forskolin, prostacyclin (PGl2) and iloprost (a stable PGl2 mimetic). 4. Octimibate increases cyclic AMP concentrations in platelets and increases the cyclic AMP-dependent protein kinase activity ratio. Octimibate stimulates adenylyl cyclase activity in human platelet membranes, with an EC50 of 200 nM. The maximal achievable activation of adenylyl cyclase by octimibate is 60% of that obtainable with iloprost. Octimibate has no effect on the cyclic GMP-inhibited phosphodiesterase (phosphodiesterase-ITI), which is the major cyclic AMP-degrading enzyme in human platelets.5. Octimibate inhibits, apparently competitively, the binding of [3H]-iloprost (a stable PGl2 mimetic) to platelet membranes; the estimated Ki is 150 nm. 6. The platelets of different species show considerable differences in the apparent potency of their inhibition of aggregation by octimibate; platelets from cynomolgus monkeys are 3 fold more sensitive than those from humans, while rat, cat and cow platelets are 50, 100, and 250 fold less sensitive than human platelets. The sensitivity of these different species to iloprost, however, varies over a range of only 10 fold with no obvious difference between primates and non-primates. 7. Octimibate appears to be a potent agonist (aggregation), or partial agonist (adenylyl cyclase), at prostacyclin receptors and is the first non-prostanoid agent of this type to be identified. The species differences in relative potency of octimibate and iloprost may reflect the existence of receptor subtypes.

Adenylyl Cyclases↗
PubMed1991

Primate vascular responses to octimibate, a non-prostanoid agonist at the prostacyclin receptor.

1. Octimibate is a potent inhibitor of human platelet aggregation, and appears to act (at least in part) through the prostacyclin receptor, as described in the preceding paper. Here, the vascular effects, both in vitro and in vivo, of octimibate have been compared to those of the stable prostacyclin (PGI2) mimetic, iloprost. Since octimibate shows extensive species variation and is potent at inhibiting platelet aggregation in primates, all of the experiments reported here have been carried out with primate tissue or in vivo in cynomolgus monkeys. 2. Activation of adenylyl cyclase in human lung membranes appears to involve stimulation of the vascular PGI2 receptor. Octimibate, as well as iloprost, stimulates adenylyl cyclase in this preparation. The EC50 values for iloprost and octimibate are 50 nM and 340 nM respectively. These values are similar to those seen with human platelet membranes. As with platelets, the maximal activation achievable with octimibate is 60% of that seen with iloprost. This result suggests that octimibate is a partial agonist for stimulation of adenylyl cyclase. 3. Iloprost (10-100 nM) relaxes human coronary and mesenteric artery precontracted with KCl, and also relaxes cynomolgus monkey aorta precontracted with phenylephrine. Octimibate appears to be a partial agonist for relaxation of human coronary artery precontracted with KCl; the intrinsic activity of octimibate (10 microM) is 0.15 compared to iloprost, and octimibate surmountably antagonizes the relaxant effects of iloprost with a Kp of 200 nM. Octimibate (up to 10 microM) evokes only weak relaxation of human mesenteric artery (precontracted with KCl) and cynomolgus monkey aorta (precontracted with phenylephrine). 4. The effects of iloprost and octimibate were compared in vivo in cynomolgus monkeys. In addition to inhibiting ex vivo platelet aggregation, both compounds cause hypotension with little effect on heart rate. The dose-response curves for inhibition of ex vivo platelet aggregation and a fall in mean arterial blood pressure were compared. The dose-separation (i.e., the relative differences in effective concentrations) for the two responses is similar with both iloprost and octimibate. 5. Since the pern; beral resistance vessels are intimately involved in regulation of systemic arterial blood pressure, the effects of both agents were tested on human peripheral resistance vessels (150-400pm diameter) in vitro. These vessels are relaxed by both iloprost and octimibate following precontraction with KCI. The IC50 value for iloprost is 44nM, and 1.7 microM octimibate evokes 50% of the maximal relaxation obtained with iloprost. Thus, the relative potencies of the two compounds in relaxing human subcutaneous resistance vessels are similar to their relative potencies in inhibiting platelet responses. This result correlates with the lack of platelet versus vascular selectivity seen with the in vivo monkey studies. 6. These results suggest that octimibate, a partial agonist at the prostacyclin receptor, is unable to discriminate between platelet and vascular prostacyclin receptors in primates.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

A kinetic survey of US hemodialysis prescriptions.

Recent reports indicate increasing mortality correlated to reduced treatment time (t) in hemodialysis (HD) patients. HD prescriptions for 101 patients visiting our unit were subjected to kinetic analysis to assess the amount of dialysis prescribed (Kt/V) and its relationship to t. The analysis showed (1) 98% of the prescriptions were empirical; (2) Kt/V was strongly correlated to protein intake (normalized protein catabolic rate [NPCR], g/kg/d), r = 0.50, N = 101; (3) Kt/V was strongly correlated to t, y = 0.50 + 0.54x, r = 0.54, and fell below 1 when t less than or equal to 3.5 hours; (4) a prescription flux deficit appeared and increased exponentially as t fell below 3.7 hours. These results suggest that in clinical practice, t is individualized as a function of predialysis BUN and is reduced when BUN is low due to low NPCR because of a perceived need for less dialysis. Because of this practice, reduced t is often associated with inadequate dialysis, and kinetic modeling of the interrelationship between blood urea nitrogen (BUN), NPCR, and Kt/V is required to assure adequate dialysis with reduced t.

Blood Urea Nitrogen↗
PubMed1990

Segregation of discrete GS alpha-mediated responses that accompany homologous or heterologous desensitization in two related somatic hybrids.

1. Prostacyclin and adenosine A2 receptors activate adenylate cyclase in the neuroblastoma hybrid cell lines NG108-15 and NCB-20. Prolonged exposure of NG108-15 cells to iloprost (a stable analogue of prostacyclin) results in a subsequent reduction in the capacity for adenylate cyclase activation by iloprost, the adenosine analogue 5'-(N-ethyl)-carboxamidoadenosine (NECA) or NaF. In contrast prolonged exposure of NCB-20 cells to iloprost results only in the loss of iloprost responsiveness. 2. Iloprost pretreatment of NG108-15 cells also magnified the morphine-dependent inhibition of iloprost-stimulated adenylate cyclase activity from 36 to 48%. This change was not due to lower iloprost stimulation following desensitization, since the % inhibition of adenylate cyclase activity by morphine in control cells was constant irrespective of enzyme activity. 3. These heterologous effects observed in NG108-15 cells following iloprost pretreatment may involve changes in the GS alpha protein, since there was a reduction of about 30% in the cholera toxin-induced [32P]-ADP-ribosylation of a 45 kDa protein from cell membranes (corresponding to the extent of loss of NECA or NaF responsiveness). A similar reduction was not observed in NCB-20 cells. 4. These results indicate that iloprost pretreatment induces different forms of desensitization in NG108-15 and NCB-20 cell lines. The heterologous desensitization in the former may, like the human platelet, involve a functional loss of GS alpha from the cell membrane. Changes in the activity of GS alpha may also account for the heterologous effects on receptors that mediate inhibition of adenylate cyclase.

Adenosine↗