Biomedical subjects

G W Dorn

Publications and source records attributed to G W Dorn.

At least 19 recordsLinked to original sources

PubMed1992

Dissociation of the contractile and hypertrophic effects of vasoconstrictor prostanoids in vascular smooth muscle.

To more clearly define the physiologic roles of thromboxane (TX)A2 and primary prostaglandins (PG) in vascular tissue we examined vascular contractility, cell signaling, and growth responses. The growth-promoting effects of (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619; TXA2 agonist), PGF2 alpha, and PGE2 consisted of protein synthesis and proto-oncogene expression, but not DNA synthesis or cell proliferation. U46619 contracted rat aortas and increased cultured rat aortic vascular smooth muscle cell intracellular free calcium concentration [Ca2+]i, [3H]inositol monophosphate (IP) accumulation, myosin light chain phosphorylation, and protein synthesis ([3H]leucine incorporation) with EC50 values ranging from 10 to 50 nM. Each of these responses was inhibitable with the TXA2 receptor antagonist [1S]1 alpha,2 beta(5Z),3 beta,4 alpha-7-(3-[2- [(phenylamino)carbonyl]hydrazino]methyl)-7-oxabicyclo[2.2.1]hept-2- yl-5-heptenoic acid (SQ29548). In contrast, PGF2 alpha increased [Ca2+]i, [3H]IP, and protein synthesis with EC50 values of 30-230 nM but contracted rat aortas with an EC50 of 4800 nM. PGE2 increased [Ca2+]i, [3H]IP accumulation, protein synthesis, and contracted rat aortas with EC50 values of 2.5-3.5 microM. TXA2 receptor blockade prevented PGF2 alpha- and PGE2-induced aortic contraction and cell myosin light chain phosphorylation, but not cell signaling or protein synthesis. Binding studies to vascular smooth muscle TXA2 receptors using 1S-[1 alpha,2 beta(5Z),3 alpha(1E,3S),4 alpha]-7-(3-[3-hydroxy-4-(p- [125I]iodophenoxy)-1-butenyl]7-oxabicyclo[2.2.1]hept-2-yl)-5-hepte noic acid ([125I]BOP) showed U46619, SQ29548, PGF2 alpha, and PGE2 competition for TXA2 receptor binding at concentrations similar to their EC50 values for aortic contraction, while binding competition with [3H]PGF2 alpha and [3H]PGE2 demonstrated the specificity of [125I]BOP and SQ29548 for TXA2 receptors. The results suggest that 1) PGF2 alpha- and E2-stimulated vessel contraction is due to cross-agonism at vascular TXA2 receptors; 2) PGF2 alpha stimulates TXA2 receptor-independent vascular smooth muscle protein synthesis at nanomolar concentrations, consistent with an interaction at its primary receptor; and 3) TXA2 is a potent stimulus for vascular smooth muscle contraction and protein synthesis. We suggest that the main physiologic effect of PGF2 alpha may be as a stimulus for vascular smooth muscle cell hypertrophy, not as a contractile agonist.

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

PubMed1992

Response of a human megakaryocytic cell line to thrombin: increase in intracellular free calcium and mitogen release.

The CHRF-288-11 cell line has been previously shown to exhibit properties consistent with a megakaryocytic origin. The response of these cells to thrombin has now been investigated. Thrombin treatment of CHRF-288-11 cells results in both an increase in intracellular free calcium levels and secretion of mitogenic activity and beta-thromboglobulin. Cell viability is not affected. The mitogenic activity released from the cells is due primarily to the presence of basic fibroblast growth factor. Immunohistochemical data indicate a packaging of basic fibroblast growth factor into granular structures. Trypsin and phorbol 12-myristate 13-acetate also initiate release of mitogenic activity from this cell line, whereas under non-stirred conditions collagen and ADP do not. Through measurements of intracellular calcium levels it was determined that thrombin pretreatment of cells ablates a further response to thrombin, but does not block an increase in intracellular calcium levels due to trypsin. This suggests that these two agonists may act through different mechanisms. The thrombin-induced release reaction is inhibited almost completely by the reagents hirudin and dipyridamole, and only partially by indomethacin. These data indicate that the CHRF-288-11 cell line should provide an excellent model system in which to study the packaging of factors into granules which undergo regulated release.

Calcium↗

PubMed1992

Growth factors downregulate vascular smooth muscle thromboxane receptors independent of cell growth.

Growth factors, in addition to being mitogenic, may modulate vascular smooth muscle differentiation. We tested whether serum or defined growth factors could regulate thromboxane A2 (TxA2) receptors in cultured rabbit aorta smooth muscle cells. Fetal bovine serum (10%) stimulated cell proliferation and DNA synthesis in subconfluent cell cultures. Binding of the thromboxane A2 agonist [1S-(1 alpha 2 beta(5Z),3 alpha(1E,3S),4 alpha)]-7-[3-(3-hydroxy-4-p- iodophenoxy-1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-hep tenoic acid showed a 41% decrease in TxA2 receptors in cells treated with 10% serum compared with serum-deprived (0.1%) controls. Receptor downregulation by serum was gradually reversible upon serum withdrawal. Compared with serum-deprived cells, those exposed to 10% serum also had diminished TxA2-stimulated phosphatidylinositol hydrolysis. Regulatory actions of serum on TxA2 receptors were distinguished from mitogenic effects with heparin, which prevented cell growth but did not inhibit serum-induced downregulation of TxA2 receptors. Furthermore, low concentrations of platelet-derived growth factor and basic fibroblast growth factor decreased TxA2 receptors without stimulating cell proliferation or DNA synthesis. These observations describe a previously unrecognized regulatory action of growth factors on a vascular smooth muscle vasoconstrictor receptor, an action which is independent of effects on cell proliferation or DNA synthesis.

Animals↗

PubMed1992

Regulation of response to thromboxane A2 in CHRF-288 megakaryocytic cells.

Thromboxane A2 (TxA2) is a potent platelet aggregating agent and a necessary intermediate for platelet stimulation by several other platelet agonists. A potentially important means whereby platelet responses to TxA2 could be modified in vivo is regulation of TxA2 receptors and/or effectors by platelet precursor megakaryocytes. We therefore investigated the mechanisms that regulate the response to TxA2 in CHRF-288, a cultured cell line derived from megakaryocytes. Incubation of CHRF-288 with the TxA2 agonist U-44069 resulted in a biexponential 75% decrease in subsequent TxA2 receptor-stimulated, but not thrombin-stimulated, Ca2+ release (half times of 1 and 4.7 h) and a monoexponential 57% decline in TxA2 receptor agonist binding sites (half time of 4.6 h). Desensitization with U-44069 for 24 h increased the proportion of internal TxA2 receptors from 23 to 82% of total receptors. Inhibition of endocytosis with phenylarsine oxide prevented U-44069-induced receptor downregulation but only partially inhibited desensitization of the Ca2+ response, indicating that internalization of receptors is not an immediate requirement for desensitization but that receptor internalization and degradation are both necessary for maximal desensitization. In summary, CHRF-288 megakaryocytic cells desensitize to TxA2 through incomplete functional uncoupling of receptors from Ca2+ signal transducers and delayed downregulation of TxA2 receptors via accelerated receptor internalization and degradation.

Bridged Bicyclo Compounds↗

PubMed1992

Differential megakaryocytic desensitization to platelet agonists.

Platelets are released into the peripheral circulation from the bone marrow where they arise as fragments of megakaryocyte cytoplasm. To characterize the effects of platelet agonists on megakaryocytes, we examined calcium signaling and desensitization to thrombin, the thromboxane A2 (TxA2) mimetic (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619), and platelet-activating factor (PAF) in cultured CHRF-288-11 megakaryocytic cells. Initially, we compared agonist-stimulated calcium transients in fura-2-loaded CHRF-288-11 cells and human platelets. The 50% effective concentration values for the agonists to increase free cytosolic calcium were as follows: thrombin (0.11 +/- 0.02 U/ml in CHRF, 0.19 +/- 0.03 U/ml in platelets), U46619 (147 +/- 33 nM in CHRF, 157 +/- 5 nM in platelets), and PAF [15 +/- 2 nM in CHRF, 16 +/- 2 nM in platelets (n = 4 each)]. CHRF-288-11 thrombin, TxA2, and PAF receptors were demonstrated to be coupled to phospholipase C because each of the agonists stimulated phosphatidylinositol hydrolysis in myo-[3H]inositol-loaded CHRF-288-11 cells and pharmacological inhibition of phospholipase C-blunted agonist-stimulated calcium signaling. CHRF-288-11 cells exposed to the three agonists for 1 h showed different patterns and extent of homologous and heterologous desensitization. Protein kinase C activation appeared to be necessary but not sufficient for desensitization because 1) activation of protein kinase C with phorbol 12-myristate 13-acetate inhibited the calcium responses to all three agonists, 2) inhibition of protein kinase C with staurosporine attenuated subsequent desensitization to each agonist, and 3) each agonist increased protein kinase C activity in CHRF-288-11 cell homogenates.

Blood Platelets↗

PubMed1992

Thrombin, but not thromboxane, stimulates megakaryocytic differentiation in human megakaryoblastic leukemia cells.

Physiologic stimuli for differentiation of bone marrow megakaryoblasts, a critical event leading to formation of platelets, have not been identified. Therefore, we examined the effects of two potent platelet agonists, thrombin and the thromboxane A2 mimetic U46619 [(15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z, 13E-dienoic acid], on the developmental regulation of cultured CHRF-288-11 megakaryoblast cells. Both thrombin and U46619 increased intracellular free calcium in fura-2 loaded, serum-deprived CHRF-288-11 cells with EC50 values of 0.07 +/- 0.01 U/ml and 194 +/- 27 nM, respectively (n = 4 each). Thrombin, but not U46619, increased intracellular pH from 7.44 +/- 0.03 to 7.55 +/- 0.06 (n = 4, P = .012) in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells. Because increases in cytosolic free calcium and/or cytosolic pH are associated with mitogenic responses in many cell systems, we determined if thrombin or U46619 stimulated CHRF-288-11 proliferation or differentiation. U46619 (1 microM) inhibited cell growth but had no effect on cell size or morphology. In contrast, thrombin (0.2 U/ml) inhibited cell division and increased overall cell size to 116 +/- 2% of control (P less than .05). Microscopically, thrombin-treated cells had increased cytoplasmic content, nuclear lobulation and nucleolar content--hallmarks of megakaryocytic differentiation. Thrombin, but not U46619, increased levels of CHRF-288-11 c-fos and c-myc mRNA transcripts (protooncogene expression). We conclude that thrombin, but not thromboxane A2, induces terminal megakaryocytic differentiation of CHRF-288-11 cells. This suggests that thrombin may act as a physiologic regulator of platelet formation in vivo.

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

PubMed1991

Human platelet aggregation and shape change are coupled to separate thromboxane A2-prostaglandin H2 receptors.

The relationships of human platelet thromboxane A2-prostaglandin H2 (TxA2/PGH2) receptor occupation as assessed by equilibrium binding of the TxA2/PGH2 agonist [125I]BOP to the functional responses of I-BOP-induced platelet shape change and aggregation were determined before and after specific, irreversible inactivation of platelet TxA2/PGH2 receptors with the photolyzable TxA2/PGH2 antagonist I-PTA-PON3. I-BOP stimulated platelet shape change and aggregation with concentrations producing a half-maximal response of 173 +/- 39 pM (n = 4) and 1.8 +/- 0.4 nM (n = 6), respectively (means +/- SE). Covalent inactivation of TxA2/PGH2 receptors with I-PTA-PON3 caused rightward shifts of I-BOP shape change and aggregation dose-response curves and resulted in pharmacological dissociation constants (Kd) of 134 pM and 1.95 nM, respectively. Isotherms of [125I] BOP binding to intact platelets (n = 6) were shallow with Hill coefficients of -0.68 +/- 0.03 and were best described by a two-site model with 222 +/- 58 sites/platelet of high affinity (Kd = 270 +/- 60 pM) and 818 +/- 90 sites/platelet of lower affinity (Kd = 3.9 +/- 1.2 nM). The relationship of I-BOP occupancy of high-affinity receptors to shape-change responses was linear (r = 0.97, P less than 0.001), but the occupancy-response relationship for the lower affinity receptor and platelet aggregation was hyperbolic with half-maximal aggregation occurring after occupation of 25% of the receptors. After covalent inactivation of a variable proportion of the receptors with I-PTA-PON3, the occupancy-response relationship for platelet aggregation resulted in a similar hyperbola indicating an excess of low-affinity receptors coupled to aggregation (spare receptors).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗

PubMed1991

Tissue- and species-specific differences in ligand binding to thromboxane A2 receptors.

The ligand binding site of vascular smooth muscle (VSM) and platelet thromboxane A2 (TxA2) receptors was characterized in humans and rabbits using the TxA2 mimetic [125I]BOP. Vessel contraction and platelet aggregation studies demonstrated that unlabeled I-BOP and the prostaglandin H2 (PGH2) mimetic U-46619 were potent agonists in rabbit aortas, human saphenous veins, and washed human and rabbit platelets. [125I]BOP bound saturably to a single site on cultured vascular smooth muscle (VSM) cells from rabbit aortas and human saphenous veins with dissociation constants (Kd) of 392 +/- 8 (n = 5) and 390 +/- 120 pM (n = 6) and binding capacities (Bmax) of 5,322 +/- 200 and 2,017 +/- 322 sites/cell, respectively. [125I]BOP also bound saturably to one site on rabbit platelets (Kd = 415 +/- 15 pM, Bmax = 594 +/- 43 sites/platelet, n = 4) but, in agreement with previous studies, to two sites on human platelets (high-affinity Kd = 118 +/- 24 pM, Bmax = 121 +/- 33 sites/platelet; low-affinity Kd = 1.1 +/- 0.47 nM, Bmax 232 +/- 23 sites/platelet, n = 4). [125I]BOP was displaced from its binding site on rabbit and human VSM and platelets by stable TxA2/PGH2 analogues possessing either agonist or antagonist activity but not by other prostaglandins. The rank orders of the binding inhibition constants (IC50) for the TxA2/PGH2 analogues were compared among the four tissues and were highly correlated (r = 0.963) in VSM and platelets from rabbits but not humans (r = 0.699), suggesting that human VSM TxA2 receptors may be distinct from platelet TxA2 receptors. The IC50 rank order was also highly correlated (r = 0.935) between human and rabbit platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Mechanism for homologous downregulation of thromboxane A2 receptors in cultured human chronic myelogenous leukemia (K562) cells.

Desensitization of the biologic response to thromboxane A2 (TXA2) mimetics has been observed ex vivo in human platelets due to TXA2 receptor uncoupling and downregulation. To define more clearly the mechanisms of homologous TXA2 receptor downregulation, the effects of the TXA2 mimetics U44069 ([15S)-hydroxy-9,11- (epoxymethano) prostadienoic acid] and I-BOP ([1S-(1 alpha 2 beta(5Z),3 alpha(1E,3S),4 alpha))-7-[3-(3-hydroxy-4- (p-iodophenoxy)-1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5 -heptenoic acid) on receptor-mediated calcium fluxes and on ligand binding to TXA2 receptors were studied in the K562 cultured human leukemic cell line which possesses many platelet characteristics. Incubation with U44069 resulted in a time-dependent decrease in the amplitude of TXA2 receptor-mediated intracellular free calcium transients. Under the same conditions, binding of [125I] BOP demonstrated a concurrent loss of K562 plasma membrane binding sites to approximately one-third the original number. The loss of [125I]BOP binding was prevented by coincubation with the TXA2 antagonist SQ29548 ([1S-1 alpha,2 beta (5Z), 3 beta,4 alpha]-7- (3-[2-[phenylamino)-carbonyl) hydrazino) methyl)-7-oxabicyclo-(2.2.1)- heptan-2-yl)-5-heptenoic acid]) and was reversed upon removal of U44069 from the culture medium. SQ29548 alone had no affect on receptor density or affinity. Loss of surface receptors was demonstrated to be mediated by agonist-occupied receptor internalization which was inhibited by incubation at 4 degrees C and did not occur with antagonist occupation. The results indicate that homologous downregulation of TXA2 receptors in K562 cells occurs by agonist-mediated active internalization of plasma membrane TXA2 receptors.

Binding, Competitive↗

PubMed1990

Cyclic oxidation-reduction reactions regulate thromboxane A2/prostaglandin H2 receptor number and affinity in human platelet membranes.

The radiolabeled thromboxane A2/prostaglandin H2 (TXA2/PGH2) agonist 125I-BOP bound to the TXA2/PGH2 receptor on human platelet membranes. Scatchard analysis showed that pretreatment of platelet membranes with the reducing agent dithiothreitol (DTT) (10 mM) for 10 min decreased maximal 125I-BOP binding (Bmax) from 1.51 +/- 0.11 pmol/mg to 0.51 +/- 0.05 pmol/mg (p = 0.001) and increased the affinity of the remaining binding sites (Kd = 647 +/- 64 pM (untreated), 363 +/- 46 pM (treated), p = 0.006). Prolonged incubation of membranes with DTT (10 mM) for 40 min further reduced the Bmax to 0.23 +/- 0.08 pmol/mg (p = 0.001 from untreated), and the binding affinity remained elevated (Kd = 334 +/- 117 pM, p = 0.035 from untreated). Kinetic analysis of 125I-BOP binding indicated that the apparent increase in binding affinity after DTT treatment was due exclusively to an increase in the rate of ligand-receptor association with no change in dissociation rate. The effects of DTT on 125I-BOP binding were dose-dependent with an EC50 of 8.1 +/- 0.2 mM. DTT inactivation of TXA2/PGH2 receptors was time-dependent with a second order rate constant (k2) of 0.123 M-1 s-1 at 20 degrees C. The platelet membrane 125I-BOP binding site was partially protected from DTT inactivation by prior occupation with the ligand. TXA2/PGH2 receptor protection by I-BOP was dose-dependent and linearly related (r = 0.97, p = 0.002) to the proportion of receptors occupied, but was incomplete since agonist occupation of 89% of the total number of receptors resulted in only a 38% protective effect. Inhibition of 125I-BOP binding after reduction with DTT could be made permanent by addition of the sulfhydryl alkylating agent N-ethylmaleimide (25 mM), but was completely reversed by reoxidation with dithionitrobenzoic acid (DTNB) (5 mM). Oxidation of untreated receptors with DTNB resulted in a 64% increase in 125I-BOP binding sites from 1.65 +/- 0.12 pmol/mg to 2.70 +/- 0.08 pmol/mg (p = 0.013) without affecting binding affinity. DTNB-induced increases in 125I-BOP binding were concentration-dependent with an EC50 of 668 +/- 106 microM and occurred in less than 1 min at 37 degrees C. In the absence of DTT, alkylation of free sulfhydryl groups with N-ethylmaleimide reduced 125I-BOP Bmax in platelet membranes to 0.85 +/- 0.08 pmol/mg (p = 0.003), but did not change the affinity of the remaining receptors. The EC50 for N-ethylmaleimide inactivation of TXA2/PGH2 receptors was 139 +/- 8 mM, and the k2 in time course experiments was 0.067 M-1 s-1 at 20 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Platelets↗

PubMed1990

Increased platelet thromboxane A2/prostaglandin H2 receptors in patients with acute myocardial infarction.

Platelets have been implicated in the formation of occlusive intracoronary thrombi leading to unstable angina pectoris and acute myocardial infarction. Evidence of platelet involvement in these syndromes includes increased thromboxane A2 synthesis during ischemic events and enhanced in vitro sensitivity to agonists. To determine the density and affinity of platelet thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors in patients with acute myocardial infarction and unstable angina pectoris, the maximum number of binding sites (Bmax) per platelet and the dissociation constant (Kd) of the TXA2/PGH2 receptor antagonist, [125I]-PTA-OH, was determined at equilibrium in washed platelets. Patients with acute myocardial infarction had a significantly (p = 0.006) higher Bmax (4,468 +/- 672 sites/platelet, n = 9) compared with controls (2,206 +/- 203 sites/platelet, n = 8). Restudied at a time when the patients' coronary artery disease was clinically stable, Bmax values for the myocardial infarction group had returned to within normal limits. The dissociation constant for [125I]-PTA-OH was not significantly different in the acute myocardial infarction patients compared with controls. In patients with acute myocardial infarction, the duration of chest pain was positively correlated (r = 0.71, p less than 0.02) with the number of [125I]-PTA-OH binding sites (Bmax). In vitro platelet sensitivity to the TXA2/PGH2 mimetic, U46619, was assessed in aggregation studies. The maximal velocity of aggregation (slope) correlated with platelet TXA2/PGH2 receptor number (r = 0.67, p less than 0.001) and was significantly higher (p less than 0.02) in the acute myocardial infarction patients compared with the other study groups. There was no significant difference in the aggregation EC50 values for the thromboxane mimetic U46619 between unstable angina, acute myocardial infarction, and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Isoelectric and mass characterization of human platelet thromboxane A2/prostaglandin H2 receptors.

To further characterize the human thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor, preparative isoelectric focusing (IEF) was performed on solubilized platelet membranes. TXA2/PGH2 receptors, assayed by specific binding of the TXA2/PGH2 antagonist [125I]PTA-OH, were electrofocused at pH 5.6. Scatchard analysis of IEF fraction pH 5.6 revealed a 180-fold concentration of TXA2/PGH2 receptors (Bmax = 3650 +/- 228 pM/mg focused, 19 +/- 4 pM/mg unfocused) with no change in binding affinity (Kd = 47 +/- 7 nM focused, 36 +/- 14 nM unfocused). SDS-polyacrylamide gel electrophoresis of photoaffinity-labelled electrofocused receptors revealed concentration of specifically labelled proteins having molecular masses of 49,000 and 27,000 Daltons. These results suggest that the human platelet TXA2/PGH2 receptor has a pI of 5.6, molecular mass of 49,000 Daltons, and may exist as a dimer. Preparative IEF should prove useful in the eventual purification of this receptor.

Affinity Labels↗

PubMed1989

Binding of an [125I] labelled thromboxane A2/prostaglandin H2 receptor agonist to baboon platelets.

To characterize the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor on baboon platelets the binding of [125I]BOP was studied. [125I]BOP bound to washed baboon platelets in a saturable manner. Scatchard analysis of binding isotherms revealed a Kd of 1.12 +/- 0.08 nM and a binding capacity of 54 +/- 5 fmoles/10(8) platelets (326 sites/platelet). Several TXA2/PGH2 agonists and antagonists displaced [125I]BOP from its baboon platelet binding site with a rank order of potency similar to human platelets: I-BOP greater than SQ29548 greater than U46619 = I-PTA-OH greater than PTA-OH. I-BOP aggregated washed baboon platelets with an EC50 of 10 +/- 4 nM. The results indicate that [125I]BOP binds to the TXA2/PGH2 receptor on baboon platelets and that this receptor is similar to its human counterpart.

Animals↗

PubMed1989

Supernormal ejection performance is isolated to the ipsilateral congenitally pressure-overloaded ventricle.

Congenital left ventricular pressure overload is associated with "excessive" hypertrophy that leads to subnormal afterload (wall stress), permitting enhanced ventricular ejection performance. Whether congenital right ventricular pressure overload is associated with a similar phenomenon is uncertain. It is also unknown whether supranormal ejection performance affects only the overloaded ventricle or is a general process affecting both ventricles. Conflicting data exist about whether the hypertrophic process associated with pressure overload is induced primarily by local loading conditions or by neuroendocrine influences. If the former postulate is true, the hypertrophic response should be confined to the overloaded ventricle; if the latter is true, one might predict that both ventricles would be affected by a less specific response to circulating catecholamines. To help resolve these issues, both right and left ventricular performance was examined in seven patients with isolated congenital pulmonary stenosis (average pulmonary pressure gradient 78 +/- 13 mm Hg), six patients with isolated congenital aortic stenosis (average gradient 80 +/- 10 mm Hg) and six normal subjects. Right ventricular ejection fraction was increased in patients with pulmonary stenosis (61 +/- 2%) compared with the value in normal subjects (53 +/- 2%, p less than 0.01) and in patients with aortic stenosis (50 +/- 3%, p = 0.007). Left ventricular ejection fraction was increased in patients with congenital aortic stenosis (84 +/- 4%) compared with the value in normal subjects (70 +/- 4%, p less than 0.01) and in patients with congenital pulmonary stenosis (65 +/- 2%, p less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve Stenosis↗

PubMed1989

Distinct platelet thromboxane A2/prostaglandin H2 receptor subtypes. A radioligand binding study of human platelets.

Thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) may aggregate platelets via a common membrane receptor(s). To further characterize this receptor, binding of the radiolabeled TXA2/PGH2 mimetic [125I]BOP to washed human platelets (WP) was investigated. [125I]BOP was competitively displaced from its platelet binding site by stable TXA2/PGH2 analogues. Competition curves were shallow with Hill coefficients of -0.73 +/- 0.05 (P less than 0.001 different from unity) (90 +/- 1% specific binding). Scatchard plots were curvilinear and most consistent with two binding sites; a high-affinity site with Kd of 234 +/- 103 pM, Bmax of 0.7 +/- 0.3 pM/mg protein (180 +/- 87 sites/WP), and a lower affinity site with Kd of 2.31 +/- 0.86 nM, Bmax of 2.2 +/- 0.3 pM/mg protein (666 +/- 65 sites/WP). [125I]BOP association and dissociation kinetics gave a Kd of 157 pM without evidence of negative cooperativity. The EC50 for I-BOP-induced initial Ca2+ increase was 209 +/- 24 pM, shape change was 263 +/- 65 pM, and aggregation was 4.4 +/- 0.5 nM. Parallel binding studies using the TXA2/PGH2 receptor antagonist [125I]PTA-OH showed a single binding site. The rank order for TXA2/PGH2 analogues to displace [125I]PTA-OH was identical to that for [125I]BOP. These studies indicate that [125I]BOP binds to two distinct sites on human platelets that may represent platelet TXA2/PGH2 receptor subtypes. The close correlation of IC50 values for I-BOP-induced platelet shape change and aggregation with the two Kds for [125I]BOP binding suggests that these platelet responses may be independently mediated by the two putative receptors.

Binding Sites↗

PubMed1989

Left ventricular dysfunction in symptomatic mitral valve prolapse.

Idiopathic MVP is characterized by a late systolic click or murmur from myxomatous mitral valvular dysfunction. It may be complicated by atypical chest pain, ventricular arrhythmias, and ECG changes that can mimic the symptoms of coronary artery disease. We prospectively performed radionuclide cineangiograms before and after stress tests in MVP patients with chest pain compared with asymptomatic MVP patients and symptomatic normal control patients. In ten patients with MVP, chest pain, and normal coronary anatomy, the LVEF remained essentially unchanged (increase of -0.5 +/- 4 percent) after exercise. In ten patients with MVP and no chest pain and in nine with normal cardiovascular system and chest pain, the exercise LVEF increased by 11.5 +/- 2 percent (p less than 0.05) and 17.4 +/- 3 percent (p less than 0.005), respectively. The resting LVEF was significantly lower (p less than 0.02) in the symptomatic MVP patients (59 +/- 3 percent) than in the asymptomatic MVP (76 +/- 5 percent) or symptomatic normal patient control subjects (70 +/- 3 percent). Patients with MVP and chest pain had a lower resting LVEF and an abnormal left ventricular functional response to exercise compared with asymptomatic MVP patients or symptomatic normal subjects. Therefore, exercise radionuclide ventriculography may not adequately differentiate between chest pain due to MVP or coronary artery disease.

Cineangiography↗

PubMed1988

Alterations in left ventricular geometry, wall stress, and ejection performance after correction of congenital aortic stenosis.

Children with congenital aortic stenosis have "excessive" left ventricular hypertrophy with reduced resting systolic wall stress that allows for supernormal ejection performance. If aortic stenosis is uncorrected, this pattern persists until adulthood. The effect of removing the aortic pressure gradient on left ventricular hypertrophy and wall stress in children with congenital aortic stenosis is unknown. To test the hypothesis that removal of the stimulus for hypertrophy by aortic valve replacement or repair would normalize left ventricular mass and wall stress, we measured left ventricular ejection performance, wall stress, and contractile function in seven patients at cardiac catheterization before and 36 +/- 7 months after surgical correction of congenital aortic stenosis. After aortic valve replacement or repair, the aortic valve gradient fell from 87 +/- 12 to 7 +/- 4 mm Hg, and peak left ventricular pressure fell from 187 +/- 14 to 128 +/- 8 mm Hg. Left ventricular ejection fraction decreased postoperatively from 86 +/- 4% to 74 +/- 4% (p less than 0.001), whereas velocity of circumferential fiber shortening decreased from 2.15 +/- 0.15 to 1.6 +/- 0.11 (p less than 0.002). Left ventricular mass remained unchanged preoperatively (121 +/- 14 g/m2) and postoperatively (121 +/- 16 g/m2), but wall thickness (h) decreased in relation to ventricular radius (r) (h/r = 0.55 +/- 0.05 preoperatively, 0.36 +/- 0.02 postoperatively; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗

PubMed1987

Decrease in agonist affinity for human platelet thromboxane A2/prostaglandin H2 receptors induced by a platelet-derived supernatant.

Platelets possess membrane receptors which mediate the aggregatory response to thromboxane A2 (TXA2) and prostaglandin H2 (PGH2). It has been observed recently that the affinities for a series of TXA2/PGH2 mimetics are decreased in crude human platelet membranes and solubilized membranes compared to intact washed platelets. The present study investigated the notion that platelets contain a substance that is released during platelet lysis that reduces the affinity of the TXA2/PGH2 receptor for agonists. The displacement of 9,11-dimethylmethano-11,12-methano-16-(3-iodo-4-hydroxyphenyl)-13, 14-dihydro-13 - aza-15 alpha beta-omega-tetranor-TXA2 ([125I]PTA-OH), a TXA2/PGH2 receptor antagonist, from its binding site in intact washed platelets by TXA2/PGH2 mimetics and antagonists was characterized in the presence or absence of the supernatant (50,000 g) obtained from sonicated platelets. In the presence of the supernatant, there was a significant (P less than 0.025) increase in the IC50 values for the TXA2/PGH2 mimetics U46619, SQ26655, and ONO11113. The increase in the IC50 for U46619 induced by the supernatant was abolished by either boiling or treating the supernatant with trypsin. The supernatant did not affect the Kd or Bmax of [125I]PTA-OH or the IC50 of the TXA2/PGH2 antagonist, SQ29548. Pretreatment of the platelets with the supernatant resulted in a significant (P less than 0.02) reduction in the aggregation response induced by U46619. Gel filtration (Sephacryl S200) of the supernatant revealed a fraction (molecular weight approximately 100,000 daltons) which significantly increased the IC50 for U46619 to displace [125I]PTA-OH from its binding site. Thus, human platelets appear to possess a protein(s) that is released into the supernatant upon sonication and inhibits the binding of TXA2/PGH2 agonists but not antagonists to their receptor. This protein may play a role in the regulation of platelet responses to the aggregatory stimuli TXA2/PGH2.

Blood Platelets↗