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R M Graham

Publications and source records attributed to R M Graham.

At least 73 records · Page 4Linked to original sources
PubMed1994

Gh: a GTP-binding protein with transglutaminase activity and receptor signaling function.

The alpha 1-adrenergic receptors activate a phospholipase C enzyme by coupling to members of the large molecular size (approximately 74 to 80 kilodaltons) G alpha h family of guanosine triphosphate (GTP)-binding proteins. Rat liver G alpha h is now shown to be a tissue transglutaminase type II (TGase II). The transglutaminase activity of rat liver TGase II expressed in COS-1 cells was inhibited by the nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) or by alpha 1-adrenergic receptor activation. Rat liver TGase II also mediated alpha 1-adrenergic receptor stimulation of phospholipase C activity. Thus, G alpha h represents a new class of GTP-binding proteins that participate in receptor signaling and may be a component of a complex regulatory network in which receptor-stimulated GTP binding switches the function of G alpha h from transglutamination to receptor signaling.

Amino Acid Sequence↗
PubMed1994

The high affinity state of the beta 2-adrenergic receptor requires unique interaction between conserved and non-conserved extracellular loop cysteines.

A disulfide bond between two extracellular cysteines, conserved in all G-protein-coupled receptors, is believed to be critical for stabilization of the ligand-binding pocket. The beta 2-adrenergic receptor (beta 2-AR) contains two conserved cysteines (Cys106 and Cys184) as well as two other extracellular cysteines (Cys190 and Cys191). The specificity of the interactions between these four cysteines has not yet been clearly established. Mutants encoding alanines for specific extracellular cysteines in the beta 2-AR gene were constructed and expressed in COS-1 and Chinese hamster ovary cells. Ala106, Ala184,190,191, and Ala106,184,190,191 mutants displayed low affinity for the beta-antagonist, 125I-cyanopindolol and insensitivity to dithiothreitol (DTT). The Ala106,191 mutant displayed an intermediate affinity and DTT sensitivity. Mutants Ala184, Ala184,190, and Ala184,191 displayed high affinity and DTT sensitivity, indicating that a solvent-accessible disulfide bond(s) is present in these mutant receptors as in the wild-type beta 2-AR. Additionally, thermal stability studies provided evidence that the extracellular disulfide bonds are essential for stabilization of the high affinity state of the receptor. These studies indicate that the covalent linkage between loops 1 and 2 of the beta 2-AR extracellular domains involves the formation of disulfide bonds, uniquely between Cys106 and Cys191, and Cys184 and Cys190, and is, thus, distinct from that of other G-protein-coupled receptors.

Amino Acid Sequence↗
PubMed1994

Identification of the diastereomers of pentobarbital N-glucosides excreted in human urine.

A study was undertaken to determine if humans excreted pentobarbital N-glucosides as urinary metabolites following oral administration of pentobarbital. (1'RS,5RS)-1-(beta-D-Glucopyranosyl)pentobarbital ((1'RS,5RS)-PTBG) was isolated from the urine of one subject. The two diastereomers, (1'RS,5R)-PTBG and (1'RS,5S)-PTBG were separated and found to be identical to synthetic standards when compared using HPLC retention times coupled with UV (with and without post-column ionization) and mass spectrometry (HPLC/MS). A HPLC method was developed for detecting and quantifying (1'RS,5R)-PTBG, (1'RS,5S)-PTBG and pentobarbital in urine. Following a single oral dose of sodium pentobarbital to male subjects (n = 6), 1.6-6.2% of the pentobarbital dose was excreted as (1'RS,5S)-PTBG over 60 hours. (1'RS,5R)-PTBG was also detected in one subject and accounted for 0.3% of the pentobarbital dose. Using a modified HPLC system, the four pentobarbital N-glucosides were resolved and analysis of a partially purified pentobarbital N-glucoside extract from one subject indicated that only (1'R,5R)-PTBG and (1'S,5S)-PTBG could be detected as urinary excretion products. These results indicate that the side chain chirality of pentobarbital may influence the observed enantioselectivity for the formation and/or urinary excretion of the pentobarbital N-glucosides.

Adult↗
PubMed1994

Plasma degradation of platelet-activating factor in severely ill patients with clinical sepsis.

OBJECTIVE: To study the plasma degradation of platelet-activating factor in severely ill patients with clinical sepsis. DESIGN: A prospective, nonrandomized control study. SETTING: Intensive care unit in a university hospital. PATIENTS: Thirteen critically ill male patients with clinical sepsis, due to medical or surgical illness, and ten normal male volunteers were studied. Measurements were repeated in seven patients who survived. MEASUREMENTS AND MAIN RESULTS: The plasma activity of acetylhydrolase, the lipoprotein-associated enzyme that hydrolyses platelet-activating factor to its biologically inactive lyso-derivative was determined using an optimized enzyme assay. The plasma half-life of platelet-activating factor was also measured, along with phospholipase A2 activity, lyso-platelet-activating factor, and serum lipid concentrations. Patients results were compared with those results of normal controls and followed once in survivors. Acetylhydrolase activity in the patient group was significantly lower than in normal subjects (median 34, interquartile range 17 to 54 nmol/min/mL vs. median 60, interquartile range 56 to 80 nmol/min/mL; p < .002), while overall, the plasma half-life of platelet-activating factor did not differ significantly between the groups. However, the half-life of platelet-activating factor in six patients who died (median 3.3, range 3.3 to 4.3 mins) was significantly greater than in either survivors (median 2.1, range 1.4 to 2.9 mins; p < .001) or the normal group (median 2.5, range 2.2 to 2.8 mins; p < .001). Consistent with theoretical prediction, a significant linear relationship existed between platelet-activating factor half-life and the reciprocal of acetylhydrolase activity in the patient group (p < .05). Plasma phospholipase A2 activity was markedly increased in the patient group, while plasma lyso-platelet-activating factor and serum lipid concentrations were severely decreased. CONCLUSIONS: Depression of acetylhydrolase activity was consistent with the concentration of lipids with which it is associated. Platelet-activating factor half-life was relatively well preserved because of the nature of its relationship with enzyme activity. The half-life was prolonged in those patients with the worst outcome and the breakdown in plasma degradation of platelet-activating factor could have contributed to pathophysiology in these subjects.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1994

Brefeldin A defines distinct pathways for atrial natriuretic factor secretion in neonatal rat atrial and ventricular myocytes.

The intracellular pathways for basal atrial natriuretic factor (ANF) secretion from the heart and their correlation with ANF processing to the active form were characterized in cultured neonatal rat atrial and ventricular myocytes. Brefeldin A, a fungal antimetabolite that blocks transport of newly synthesized proteins from the endoplasmic reticulum, was used to inhibit nascent protein trafficking. Thus, release of newly synthesized hormone was blocked, but release of stored hormone was unaffected. Whereas brefeldin A inhibited basal ventricular ANF release to 10% of the control value, basal ANF release from atrial cells was enhanced. Furthermore, basal atrial ANF secretion was inhibited by agents preventing myocyte depolarization, Ca2+ influx, release of Ca2+ from intracellular stores, or activation of protein kinase C, whereas ventricular ANF secretion was unaffected by these agents. Brefeldin A did not alter maturational processing of pro-ANF to ANF-(99-126) in either atrial or ventricular cultures. These findings indicate that (1) basal secretion of ANF from ventricular cells relies largely on newly synthesized hormone and is probably constitutive, (2) basal secretion of ANF from atrial cells is independent of transport of newly synthesized protein and occurs via a regulated pathway controlled at least in part by signaling changes associated with myocyte beating, and (3) processing of pro-ANF occurs either with constitutive or regulated secretion of hormone, which may indicate multiple cellular locations for the processing enzyme.

Animals↗
PubMed1994

Cloning, expression, and tissue distribution of the rat homolog of the bovine alpha 1C-adrenergic receptor provide evidence for its classification as the alpha 1A subtype.

Three alpha 1-adrenergic receptors (ARs) have been cloned, i.e., the alpha 1B-, alpha 1C-, and alpha 1D-ARs. Compared with the alpha 1B subtype, the alpha 1A subtype in tissue is described as being insensitive to chloroethylclonidine and sensitive to SZL-49 and having a 10-100-fold higher affinity for a number of agonists and antagonists. The alpha 1A subtype is also expressed in a variety of rat tissues (as assessed by pharmacology), with greatest abundance in the cerebral cortex, hippocampus, vas deferens, and submaxillary gland. The cloned bovine alpha 1C-AR, though having an alpha 1A-AR pharmacology, was first reported as not being expressed in any rat tissue (as determined by Northern analysis) and was therefore designated as a new subtype. We report the cloning, expression, and characterization of the rat homolog of the bovine alpha 1C-AR. Using a human alpha 1C-AR probe obtained by polymerase chain reaction screening of a neuroblastoma cell line (SK-N-MC), both exon 1 and exon 2 of the rat alpha 1C-AR gene were cloned from a rat genomic library. These two exons were spliced together and cloned into the expression vector pMT2'. Transfection into COS-1 cells and analysis of the ligand-binding profile of the expressed protein receptor using 125I-HEAT revealed a 10-100-fold higher affinity for the alpha 1-AR antagonists 5-methylurapidil, (+)-niguldipine, WB-4101, and phentolamine and the agonists oxymetazoline and methoxamine, compared with the alpha 1B-AR. This ligand-binding profile is similar to that for endogenously expressed tissue alpha 1A-ARs. In addition, the rat alpha 1C-AR was the least sensitive of the three cloned subtypes to the alkylating effects of chloroethylclonidine but was the most sensitive to the alkylating prazosin analog SZL-49, properties also observed for the tissue alpha 1A subtype. Furthermore, by three different techniques, i.e., RNase protection assays, reverse transcription-polymerase chain reaction Northern blotting, and in situ hybridization histochemistry, the rat alpha 1C-AR mRNA was localized to alpha 1A-AR-rich tissues, such as rat vas deferens, hippocampus, aorta, and submaxillary gland. Taken together, these data suggest that this receptor may actually represent the alpha 1A subtype.

Amino Acid Sequence↗
PubMed1994

Platelet and plasma platelet-activating factor in sepsis and myocardial infarction.

Platelet-activating factor (PAF) is a potent phospholipid mediator which has been implicated in the pathophysiology and complications of diverse clinical illness such as myocardial infarction and shock. 10 normal males, 13 presenting with acute myocardial infarction and 13 with clinical sepsis were studied. In myocardial infarction, plasma PAF, platelet PAF receptor number and platelet-associated PAF were not significantly different from normal. In clinical sepsis, plasma PAF was not different and platelet-associated PAF was slightly, but not significantly, higher. Similarly, in this group, the production of PAF from resting and stimulated neutrophils was not different from normal. Despite significant experimental evidence from animal studies for the involvement of PAF in cardiovascular disorders, this clinical study provides little direct evidence to support this view. Our results suggest that PAF is maintained at a relatively constant circulating level, a consequence of metabolic regulation and a high avidity for platelets and neutrophils.

Adult↗
PubMed1993

Dipeptide processing activates recombinant human prochymase.

Human chymase (h-chymase) is a serine protease that efficiently converts angiotensin I to II. Its structure and homology to other serine proteases suggest that it is synthesized as a zymogen, and is processed to the active form by cleavage of a 19-residue signal peptide and of a dipeptide pro-segment. To evaluate maturational processing of this enzyme, the proteins encoded by three h-chymase cDNA constructs (wild-type, lacking the pro- or lacking the prepro-segment) were characterized after expression in COS-1 cells. These recombinant proteins were not catalytically active. Purification and NH2-terminal sequence analysis of the protein expressed from the wild-type construct revealed processing to the proenzyme. Prochymase activation was achieved by incubation with a B-cell lymphoma homogenate, which apparently contains a heterologous processing enzyme sensitive to thiol protease inhibitors. NH2-terminal sequence analysis of the activated h-chymase revealed cleavage of the pro-segment, and its biochemical characteristics were identical to those of native h-chymase purified from the myocardium. These findings indicate that processing of the dipeptide pro-segment is necessary and sufficient for activation of human chymase. Such processing is probably also required for the activation of related serine proteases, e.g., cathepsin G, which have homologous dipeptide pro-segments.

Amino Acid Sequence↗
PubMed1993

Platelet-activating factor and lipid metabolism in acute malaria.

Platelet-activating factor (PAF) contributes to a range of pathophysiological responses in severe illness. To examine PAF metabolism in acute malaria, venous blood was drawn from 10 untreated adults with falciparum malaria, from 8 with untreated vivax malaria, and from 10 controls. Plasma lyso-PAF, produced from PAF through the enzyme acetylhydrolase (AH), was bioassayed, after acetylation to PAF, by platelet [14C]-serotonin release. AH activity was measured by hydrolysis of [3H]-acetyl-PAF. Amounts of plasma lyso-PAF were lower in falciparum (median [range] 24 [9-221] ng/ml) and vivax (35 [7-236] ng/ml) infected patients than in controls (399 [212-504] ng/ml; P < 0.01), and correlated significantly with serum total and HDL-cholesterol (P < 0.001). Plasma AH activities were similar in the control, falciparum and vivax malaria groups. These data suggest that in malaria plasma lyso-PAF values fall together with other blood lipids, but independently of changes in AH activity. This may reflect a generalised decrease in lipid and phospholipid synthesis. However, the reduction of plasma lyso-PAF concentrations in our patients was much greater than that of serum lipoproteins. This is consistent with conversion of lyso-PAF to PAF or with increased PAF-receptor interactions. These two possibilities would have pathophysiological implications.

Acute Disease↗
PubMed1993

Variation in plasma platelet-activating factor degradation and serum lipids after acute myocardial infarction.

BACKGROUND: Platelet-activating factor is a biologically potent phospholipid that may mediate cell damage in patients with myocardial ischemia. In plasma, its inactivation to lyso-platelet-activating factor is catalyzed by a specific, lipoprotein-associated acetylhydrolase. Because lipoprotein levels decrease after myocardial infarction, a possible reduction was suspected to occur in plasma degradation of platelet-activating factor. METHODS: Degradation of platelet-activating factor was examined in an optimized assay of acetylhydrolase activity and in relation to the in vitro plasma half-life of platelet-activating factor. These, plasma lyso-platelet-activating factor and serum lipids, were measured in 12 men with acute myocardial infarction at presentation and at 2 and 7 days later. RESULTS: Acetylhydrolase activity was depressed at day 2 and at day 7. The corresponding increase in plasma half-life of platelet-activating factor was minimal and insignificant. A significant linear relation existed between the half-life of platelet-activating factor and the reciprocal of acetylhydrolase activity at each time of study, indicating a hyperbolic relation between the two. By day 2, total and low-density lipoprotein cholesterol had decreased but showed no further change by day 7; high-density lipoprotein cholesterol had not decreased at day 2 but was depressed by day 7. Plasma lyso-platelet-activating factor had decreased by day 2 and had returned to its initial level by day 7. CONCLUSIONS: Acute myocardial infarction is associated with depression of plasma acetylhydrolase activity, and because of the hyperbolic relation between the plasma enzyme activity and the half-life of platelet-activating factor, the latter shows negligible change. Hence, the mechanism for the inactivation of any platelet-activating factor that might be released as a consequence of tissue damage is preserved.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1993

Coupling of expressed alpha 1B- and alpha 1D-adrenergic receptor to multiple signaling pathways is both G protein and cell type specific.

alpha 1-Adrenergic receptors (ARs) are members of the G protein-coupled receptor superfamily. alpha 1-AR subtypes mediate the effects of the sympathetic nervous system, especially those involved in cardiac homeostasis. To investigate signal transduction by a novel subtype (alpha 1D), which we recently cloned, and to compare it with that by the previously characterized alpha 1B-AR, we assessed the ability of each subtype to activate polyphosphoinositide (PI) metabolism, cAMP accumulation, and arachidonic acid release in Chinese hamster ovary (CHO) and COS-1 cells expressing these subtypes after stable or transient transfection, respectively. In COS-1 and CHO cells, both the alpha 1D- and alpha 1B-AR were found to couple to PI hydrolysis through a pertussis toxin-insensitive G protein. Both alpha 1-AR subtypes also increased intracellular cAMP by an indirect mechanism, although this effect was observed only in COS-1 cells and not in CHO cells. Interestingly, alpha 1-AR-stimulated arachidonic acid release was also demonstrated for both subtypes in COS-1 cells. This release was mediated through phospholipase A2 activation and involved a pertussis toxin-sensitive G protein. alpha 1-AR-stimulated arachidonic acid release was dependent upon extracellular calcium and was inhibited by 1 microM nifedipine. Inhibitors of protein kinase C, phospholipase C, and diacylglycerol lipase did not alter alpha 1-AR-stimulated release of arachidonic acid. These findings indicate that in COS-1 cells alpha 1-AR-stimulated arachidonic acid release is most likely coupled to dihydropyridine-sensitive L-type calcium channels via a pertussis toxin-sensitive G protein. The influx of extracellular calcium then stimulates phospholipase A2 to release arachidonic acid. alpha 1-AR-stimulated arachidonic acid release could also be demonstrated in CHO cells and was pertussis toxin sensitive but nifedipine insensitive. These cells were also unresponsive to Bay K8644, indicating a lack of voltage-sensitive calcium channels in CHO cells. Nevertheless, alpha 1-AR activation increased intracellular Ca2+ levels, as assessed by fura-2 fluorescence studies. Neomycin blocked both alpha 1-AR-stimulated PI hydrolysis and increases in intracellular Ca2+ levels but did not inhibit the increase in arachidonic acid release. Taken together, these data indicate that in CHO cells alpha 1-ARs can couple directly to phospholipase A2 activation via a pertussis toxin-sensitive pathway. Thus, in these model systems we demonstrate for the first time that a single alpha 1-AR subtype can activate multiple distinct signal transduction pathways, in which receptor-effector coupling is modulated by distinct G proteins.

Animals↗
PubMed1992

Genomic organization and expression of the human alpha 1B-adrenergic receptor.

alpha 1-Adrenergic receptors (ARs) are members of the guanine nucleotide-binding protein-coupled receptor superfamily. The genes for all ARs described thus far are intronless. We report here the cloning and the nucleotide sequence of the gene for the human alpha 1B-AR. It consists of two exons and a single large intron of at least 20 kilobases which interrupts the coding region at the end of the putative sixth transmembrane domain. The deduced amino acid sequence of the encoded receptor has a high degree of homology to the cloned hamster, rat, and dog alpha 1B-ARs. To characterize the encoded protein, a fusion gene constructed by splicing together exon 1 and exon 2 was expressed transiently in COS-1 cells. The transfected gene fusion product resulted in the production of an alpha 1B-AR with ligand binding characteristics indistinguishable from those of the expressed hamster alpha 1B cDNA. Evidence that the human alpha 1B-AR gene we have isolated is indeed transcribed is the finding of similar sized (2.8-kilobase) transcripts in human heart and other tissues by Northern blot analysis when either exon 1 or exon 2 is used as a probe. Moreover, using primers designed to span the exon 1/exon 2 boundary, a polymerase chain reaction product generated from single-stranded DNA prepared from human heart mRNA had the exact size and nucleotide sequence predicted for a transcript in which exon 1 is spliced to exon 2. The 5'-flanking region (924 base pairs (bp)) of exon 1 contains neither a TATA box nor a CAAT box but is high in GC content (70%) and contains several Sp1 binding sites (GC boxes), consistent with promoters described for housekeeping genes. The 5'-untranslated region also contains a putative cyclic AMP response element. Primer extension studies and RNase protection assays suggested that there are several potential transcription start sites in most tissues with a predominant site located 173 bp upstream from the translation start site. The 3'-flanking region contains a putative polyadenylation signal (ATTAAA) 492 bp downstream from the stop codon. The genomic organization of the human alpha 1B-AR with a single large intron interrupting its coding region differs from those of other ARs as well as muscarinic and 5-hydroxy-tryptamine receptors, which are intronless. The location of the intron in the human alpha 1B-AR gene is also unique among those members of the G-protein-coupled receptor family that do possess introns.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1992

Structure and function in rhodopsin. Studies of the interaction between the rhodopsin cytoplasmic domain and transducin.

Structural requirements for the activation of transducin by rhodopsin have been studied by site-specific mutagenesis of bovine rhodopsin. A variety of single amino acid replacements and amino acid insertions and deletions of varying sizes were carried out in the two cytoplasmic loops CD (amino acids 134-151) and EF (amino acids 231-252). Except for deletion mutant delta 137-150, all the mutants bound 11-cis-retinal and displayed normal spectral characteristics. Deletion mutant delta 236-239 in loop EF caused a 50% reduction of transducin activation, whereas deletion mutant delta 244-249 and the larger deletions in loop EF abolished transducin activation. An 8-amino acid deletion in the cytoplasmic loop CD as well as a replacement of 13 amino acids with an unrelated sequence showed no transducin activation. Several single amino acid substitutions also caused significant reduction in transducin activation. The conserved charged pair Glu-134/Arg-135 in the cytoplasmic loop CD was required for transducin activation; its reversal or neutralization abolished transducin activation. Three amino acid replacements in loop EF (S240A, T243V, and K248L) resulted in significant reduction in transducin activation. We conclude that 1) both the cytoplasmic loops CD and EF are required for transducin activation, and 2) effective functional interaction between rhodopsin and transducin involves relatively large peptide sequences in the cytoplasmic loops.

Amino Acid Sequence↗
PubMed1992

Identification of 5-ethyl-5-(2-methylbutyl)barbituric acid as an impurity of manufacture in amobarbital.

Amobarbital [5-ethyl-5-(3-methylbutyl)barbituric acid], USP, was found to contain an impurity that was not associated with hydrolysis and decomposition of the barbiturate ring. The impurity was isolated by semipreparative HPLC and was identified as 5-ethyl-5-(2-methylbutyl)barbituric acid (1) by MS (electron impact and chemical ionization) and 1H NMR. The substitution pattern on the alkyl side chain was verified by using the achiral NMR shift reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2- dimethyl-3,5-octanedionato)europium(III). Older samples of amobarbital, USP, contained greater than 6% of 1, whereas recent samples of amobarbital, USP, contained less than 1% of 1. Because the pharmacological profiles of 1 and amobarbital in rodents are comparable, the impurity probably does not constitute a clinically significant problem for humans.

Amobarbital↗
PubMed1992

Plasma platelet-activating factor degradation in patients with severe coronary artery disease.

1. Platelet-activating factor is inactivated in plasma by the action of a specific acetylhydrolase that cleaves the acetate moiety from the sn-2 position. Degradation was determined under optimized conditions and under conditions closer to those which may occur in vivo. The latter, or platelet-activating factor half-life, was measured by a modified method that is simple, inexpensive and reliable. 2. A hyperbolic relationship was found to exist between the two measures of degradation, the values in both normal subjects and patients with coronary artery disease falling on the tail of the hyperbola. Thus, there is an increase in platelet-activating factor half-life associated with a lowering of acetylhydrolase activity, but this increase is relatively small. 3. There were significant direct linear relationships between acetylhydrolase activity and serum total cholesterol and low-density-lipoprotein-cholesterol concentrations in both subject groups. Although acetylhydrolase activity was most closely associated with the low-density-lipoprotein-cholesterol fraction, the activity for a given serum level of low-density-lipoprotein-cholesterol was higher in patients with coronary artery disease.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1992

Plasma platelet activating factor degradation and serum lipids after coronary bypass surgery.

OBJECTIVE: Platelet activating factor (PAF) is a potent mediator in inflammatory responses and maybe involved in various disease states. Degradation of PAF in plasma results from the action of a specific, lipoprotein associated, acetylhydrolase. The aim was to determine plasma acetylhydrolase activity under optimised conditions, PAF half life, phospholipase A2 activity, the lyso-derivative of PAF (lyso-PAF), and lipids in patients undergoing coronary artery bypass grafting. METHODS: The study variables were determined 3 d and 7 d following coronary artery surgery and compared to presurgical values in 15 males, age 55(SEM 4) years. RESULTS: Three days following coronary bypass grafting, total, LDL and HDL cholesterol fell significantly by 30%, 45%, and 15% respectively (p less than 0.001), all decreases correlating with bypass time (p less than 0.025). Concentrations remained low at 7 d (p less than 0.005). Acetylhydrolase activity fell by 38% (p less than 0.001) at 3 d post-surgery and remained depressed, but plasma PAF half life did not change after surgery. The inverse relationship between acetylhydrolase activity and plasma PAF half life preoperatively (p less than 0.01) was not evident after surgery. There was a direct linear relationship between acetylhydrolase activity and both total (p less than 0.002) and LDL cholesterol (p less than 0.001) before surgery. The fall in acetylhydrolase activity correlated with the fall in these lipids (p less than 0.01) but not with that of HDL cholesterol. Plasma lyso-PAF decreased by 65% (p less than 0.001) at 3 d and remained depressed (p less than 0.001). Plasma phospholipase A2 activity increased by 60% (p less than 0.01) and remained raised (p less than 0.05), the increase at 3 d being related to bypass time (p less than 0.05). CONCLUSIONS: The large fall in plasma acetylhydrolase activity after coronary bypass grafting is consistent with the fall in plasma lipids. However, the absence of a significant change in the measured PAF half life in plasma raises questions as to the pathophysiological significance of the decrease in acetylhydrolase activity.

Carboxylic Ester Hydrolases↗
PubMed1992

Mechanisms of alpha 1-adrenergic vascular desensitization in conscious dogs.

To investigate the mechanisms of alpha 1-adrenergic vascular desensitization, osmotic minipumps containing either saline (n = 9) or amidephrine mesylate (AMD) (n = 9), a selective alpha 1-adrenergic receptor agonist, were implanted subcutaneously in dogs with chronically implanted arterial and right atrial pressure catheters and aortic flow probes. After chronic alpha 1-adrenergic receptor stimulation, significant physiological desensitization to acute AMD challenges was observed, i.e., pressor and vasoconstrictor responses to the alpha 1-adrenergic agonist were significantly depressed (p < 0.01) compared with responses in the same dogs studied in the conscious state before pump implantation. However, physiological desensitization to acute challenges of the neurotransmitter norepinephrine (NE) (0.1 micrograms/kg per minute) in the presence of beta-adrenergic receptor blockade was not observed for either mean arterial pressure (MAP) (30 +/- 7 versus 28 +/- 5 mm Hg) or total peripheral resistance (TPR) (29.8 +/- 4.9 versus 28.9 +/- 7.3 mm Hg/l per minute). In the presence of beta-adrenergic receptor plus ganglionic blockade after AMD pump implantation, physiological desensitization to NE was unmasked since the control responses to NE (0.1 micrograms/kg per minute) before the AMD pumps were now greater (p < 0.01) than after chronic AMD administration for both MAP (66 +/- 5 versus 32 +/- 2 mm Hg) and TPR (42.6 +/- 10.3 versus 23.9 +/- 4.4 mm Hg/l per minute). In the presence of beta-adrenergic receptor, ganglionic, plus NE-uptake blockade after AMD pump implantation, desensitization was even more apparent, since NE (0.1 micrograms/kg per minute) induced even greater differences in MAP (33 +/- 5 versus 109 +/- 6 mm Hg) and TPR (28.1 +/- 1.8 versus 111.8 +/- 14.7 mm Hg/l per minute). The maximal force of contraction induced by NE in the presence or absence of endothelium was significantly decreased (p < 0.05) in vitro in mesenteric artery rings from AMD pump dogs compared with saline control dogs. Furthermore, alpha 1-adrenergic receptor density, as determined by [3H]prazosin binding in membrane preparations from vessels in the mesentery, was decreased (8.2 +/- 1.0 versus 18.4 +/- 1.4 fmol/mg protein, p < 0.001) without any change in Kd in the AMD pump dogs compared with the saline pump dogs.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Agonists↗