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Biomedical subjects

J M Gerrard

Publications and source records attributed to J M Gerrard.

179 records · Page 10Linked to original sources
PubMed1976

The influence of aspirin and indomethacin on the platelet contractile wave.

Recent evidence suggests that a short-lived product of prostaglandin biosynthesis produced on the addition of arachidonic acid to platelet microsomes is involved in physiologic platelet aggregation and mediates the release reaction by producing the platelet contractile wave. An important corollary of this hypothesis is that aspirin and indomethacin, inhibitors of prostaglandin synthesis, should block the platelet contractile process produced by agents which can initiate platelet aggregation. The present study tested this hypothesis and found that aspirin and indomethacin were, indeed, potent inhibitors of the platelet contractile wave stimulated by collagen and epinephrine, but largely failed to inhibit internal transformation induced by thrombin and ADP. The findings confirm the hypothesis that a prostaglandin produced endogenously by platelets initiates platelet contraction and suggests that ADP and thrombin have the ability to stimulate the platelet contractile apparatus by an alternate mechanism not dependent on prostaglandin synthesis.

Adenosine Diphosphate↗
PubMed1976

Localization of platelet prostaglandin production in the platelet dense tubular system.

Platelet production of 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 8-(1-hydroxy-3-oxopropyl)-9, 12L-dihydroxy-5,10-heptadecadienoic acid (PHD), two metabolites of the prostaglandin cyclic endoperoxides PGG2 and PGH2, was found in this investigation to occur primarily in a platelet microsomal fraction consisting almost exclusively of membranes. To further localize the membrane site of platelet prostaglandin biosynthesis, the present study has used a cytochemical technique employing 3,3'-diaminobenzidine as an oxidizable substrate. The reaction product was found to localize in the platelet dense tubular system. Formation of the reaction product was inhibited by aminotriazole. In similar concentrations, aminotriazole inhibited collagen and arachidonic acid aggregation, the second wave of ADP and epinephrine aggregation, but failed to inhibit aggregation by PGG2 and A23187. A study of the mechanism of action of aminotriazole revealed inhibition of formation of HHT and PHD. The results localize platelet prostaglandin biosynthesis to the membranes of the dense tubular system.

Amitrole↗
PubMed1975

Oncornavirus-like particles from cultured bone marrow cells preceding leukemia and malignant histiocytosis.

Particles with the density and enzymatic activity characteristic of known oncornavirus have been previously described in bone marrow cells from patients with leukemia in relapse and in remission. We have confirmed these findings and studied two patients in whom preleukemia was among the diagnostic considerations. Following cultivation of bone marrow from these patients for 1 week in conditioned media with dexamethasone, a high-speed pellet of the supernatant fluid and disrupted cells was prepared and analyzed on a sucrose gradient for enzymatic activity characteristic of RNA-directed DNA polymerase (reverse transcriptase). Peaks of endogenous DNA polymerase activity showing ribonuclease sensitivity and/or stimulation with the synthetic template poly(rC)-(dG)12-18 were demonstrated in both patients at densities of 1.15 to 1.19 and 1.21 to 1.24 g/ml. Subsequently, diagnosis 2 and 4 months after initial evaluation revealed acute myelogenous leukemia and malignant histiocytosis, respectively. Prior studies have suggested a possible etiological significance of such particles in human leukemia. The demonstration of similar particles preceding clinically overt disease in these patients supports this hypothesis and offers the possibility of early diagnosis and treatment.

Adolescent↗
PubMed1975

Labile aggregation stimulating substance (LASS): the factor from storage pool deficient platelets correcting defective aggregation and release of aspirin treated normal platelets.

Mixtures of equal volumes of Hermansky-Pudlak (HP) syndrome (adenine nucleotide storage pool deficient) and aspirin treated (AT) platelets (inhibited release of adenine nucleotides) undergo irreversible aggregation when exposed to collagen or adrenaline, whereas neither alone will do so. The present investigation has explored the basis for the mutual correction. Correction in the mixed system was accompanied by release of significant amounts of [14C]5-hydroxy-tryptamine from the AT platelets, whereas very little isotope was released when AT platelets alone were exposed to collagen. The correction of aggregation and the release of isotope could both be suppressed by pre-treating HP platelets with aspirin. Labile aggregation stimulating substance (LASS) composed of two closely linked intermediates of prostaglandin (PG) E2 and PGF2alpha biosynthesis, produced using a microsomal fraction of HP platelets, could correct the aggregation and secretion defect of AT platelets exposed to collagen. These findings indicate that HP platelets when mixed with AT platelets and exposed to collagen secrete a substance which is responsible for the correction. LASS, identified as the factor involved, acted as an intercellular messenger which mediated the correction by overcoming the influence of aspirin on normal cells.

Adenine Nucleotides↗
PubMed1975

The influence of prostaglandin endoperoxides on platelet ultrastructure.

Prostaglandin endoperoxides produced during aggregation of blood platelets are potent promoters of platelet aggregation and the release reaction. The present investigation has studied the effects of prostaglandin endoperoxides produced by platelet microsomes after incubation with arachidonic acid on the ultrastructure of platelets. Prostaglandin endoperoxides caused platelet pseudopod formation and internal transformation associated with a contractile wave within the platelet. The contractile process was similar to that seen following incubation of platelets with collagen or thrombin but was more complete than that seen with 25 muM ADP. Platelet aggregation was more prominent in unstirred samples incubated with the prostaglandin endoperoxides than in samples similarly incubated with 25 muM ADP. Dilatation of the open canalicular system was not a prominent feature except at 45 minutes after addition of the endoperoxides to the platelets, when the platelets appeared to be in a recovery phase. We conclude that the endoperoxides promote platelet stickiness and platelet aggregation by directly or indirectly stimulating the platelet contractile system.

Arachidonic Acids↗
PubMed1974

Hyperactivity of neutrophil leukotactic responses during active bacterial infection.

To determine if changes in neutrophil leukocyte function occur during active bacterial infection, the neutrophils of 25 patients with active bacterial infection and 25 age-matched controls were compared for leukotactic activity, random mobility, and nitroblue tetrazolium reduction. The neutrophil leukocytes of patients with bacterial infection were hyperactive in unidirectional movement toward a chemotactic stimulus as measured in the leukotactic assay and usually had increased nitroblue tetrazolium reduction. The mean leukotactic index was 165+/-56 in patients with bacterial infection and 70+/-11 in controls (P < 0.001). After 7-10 days of appropriate therapy with clinical and bacteriological response, leukotactic activity returned to normal values. A hyperactive leukotactic response continued, however, in patients with persisting bacterial infection. The hyperactive leukotactic response of circulating neutrophils appears to be an early and sensitive event in the inflammatory cycle stimulated by bacterial infection and may aid in the localization of invading bacteria.

Adolescent↗
PubMed1974

Effects of the lonophore A23187 on blood platelets I. Influence on aggregation and secretion.

A23187 is an antibiotic ionophore which transports divalent cations across cell membranes into the cytoplasm and releases cations from intracellular storage sites. The present investigation has studied the influence of A23187 on blood platelet aggregation and secretion. A23187 added to stirred C-PRP produced concentration-dependent aggregation and release of (14)C-serotonin. Calcium ions potentiated the response of platelets in washed suspensions to A23187, but they were not required for ionophore-induced aggregation or release. N-ethylmaleimide and agents which increase the level of cyclic 3',5'-adenosine monophosphate (cAMP) in platelets were effective inhibitors of A23187-induced aggregation and secretion.Platelets incubated with (45)Ca(++) before addition of A23187 increased their content of isotope by 50% within 45 seconds after exposure to the ionophore. The results indicate that an increase in the cytoplasmic concentration of calcium ions from intracellular sources may be the critical event in triggering platelet contraction and the release reaction. Increased concentrations of cAMP may inhibit the platelet response to A23187 and other aggregating agents by stimulating a calcium extrusion pump.

Adenosine↗
PubMed1974

Effects of the lonophore A23187 on the blood platelets II. Influence on ultrastructure.

A23187, an ionophore which selectively transports calcium across cell membranes into cytoplasm or releases the divalent cation from intracellular storage sites, was shown in previous studies to stimulate platelet aggregation and the release reaction. The nature of its influence on platelet function suggested that an increase in cytoplasmic calcium ion concentration might be a critical factor linking stimulation to secretion through the platelet contractile mechanism. The present investigation has examined the effects of A23187 in platelet ultrastructure and aggregation after incubation with various concentrations of the drug. Scanning and transmission electron microscopy revealed changes in the form and internal organization of platelets following exposure to A23187 that were identical to those which develop in the cells after exposure to potent agents such as collagen and thrombin. High concentrations of ionophore caused destruction of the platelets on prolonged incubation, while the effects of low concentrations on structure and aggregation reversed completely. Recovered platelets were as sensitive to other aggregating agents as control cells. The findings support the concept that platelets are a form of muscle cell and the internal transformation stimulated by A23187 and other aggregating agents is a manifestation of contractile activity. Inactivation of A23187 by plasma followed by recovery of unaltered appearance indicates that platelets have an active mechanism for reducing the level of cytoplasmic calcium.

Adenosine Diphosphate↗
PubMedDate not supplied

Increased phosphatidic acid and decreased lysophosphatidic acid in response to thrombin is associated with inhibition of platelet aggregation.

Thromboxane A2, produced from the arachidonic acid released from platelet phospholipids by phospholipase A2, stimulates platelet aggregation. It remains unresolved whether additional products of platelet phospholipase A2 might promote aggregation. To address this question, we have used aspirin-treated platelets to block thromboxane A2 formation and studied the influence of the phospholipase A2 inhibitor U10029A on platelet aggregation and secretion in response to thrombin. U10029A at 100 microM markedly inhibited platelet aggregation, but had no effect on platelet secretion. Since this concentration of U10029A effectively blocked lysophosphatidic acid (LPA) formation, LPA was added and found to substantially reverse the inhibitory effect of U10029A in these platelets. Furthermore, the action of U10029A was not due to inhibition of phosphatidate phosphohydrolase because U10029A, unlike propranolol, did not inhibit this enzyme. Although it is not possible to conclusively rule out an effect of U10029A in addition to its inhibition of phospholipase A2, our results reveal that a product of phospholipase A2 other than thromboxane A2 is important for platelet aggregation, but not for secretion in response to thrombin. Our data suggest that this product is LPA. Since the amount of phosphatidic acid (PA) increased dramatically concurrent with inhibition of platelet aggregation, it is safe to conclude that PA has no direct role to promote platelet aggregation in response to thrombin.

Arachidonic Acid↗
PubMedDate not supplied

A role for intracellular histamine in ultrastructural changes induced in platelets by phorbol esters.

In human platelets, phorbol esters, such as phorbol-12-myristate-13-acetate (PMA), induce morphological changes, including pseudopod formation and the swelling and fusion of intracellular granule membranes with those of the surface-connected canalicular system, effects which have been attributed to activation of protein kinase C. However, a novel intracellular histamine antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]-ethanamine. HCl (DPPE), previously has been shown to block PMA-induced aggregation independently of protein kinase C interaction, an effect reversible in permeabilized platelets by the addition of histamine. We now demonstrate that DPPE inhibits, in a concentration-dependent manner, the effects of PMA on human platelet ultrastructure. In permeabilized platelets, histamine reverses this inhibition, although it alone induces minimal effects on morphology. The results support a role for this amine to promote the labilization of platelet granules and pseudopod formation induced by PMA, presumably by acting in concert with additional PMA-activated pathways.

Blood Platelets↗
PubMedDate not supplied

Effect of prostaglandin on the composition of chinchilla middle ear effusion.

Prostaglandins (PGs) are naturally occurring, cyclic, unsaturated fatty acids which possess a wide range of potent biological activities. PGs have been found in human middle ear effusions and might have implications for understanding the inflammation and possibly the bone resorption seen in chronic otitis media. We have measured PGs by radioimmunoassay in middle ear effusions (MEE) from experimentally induced serous otitis media (SOM) and purulent otitis media (POM) in chinchillas. PGE2 levels were significantly higher in the POM group compared to the SOM group. We have also demonstrated that chinchilla middle ear mucosa can convert arachidonic acid (AA), a precursor of PGs, to PG by injecting 14C-AA into bullae and assaying using radiochromatography. This conversion was completely blocked by both indomethacin and aspirin given orally or by direct injection into the middle ear. We then injected 50 microgram of PGE2 into chinchilla bullae to assess its effect on the composition of MEE. First, the time course of PGE2 metabolism after its injection into the middle ear (ME) was determined by thin-layer chromatography (TLC) of labelled and unlabelled PGE2. Following this, serial daily injections of PGE2 and normal saline as control were made for one, three, and seven days. MEE and serum were collected and assayed for lactate dehydrogenase (LDH), acid and alkaline phosphatase, calcium, protein and hexosamine. Compared to the control, the levels of LDH, acid and alkaline phosphatase, calcium and protein were significantly elevated. Hexosamine levels were higher than the control at one and three days but did not differ significantly at seven days from the control. We have therefore demonstrated that chinchilla middle ear mucosa has the ability to synthesize PG from AA and suggest an active role for PGs in the inflammation and in the bone resorption seen in otitis media.

Animals↗
PubMedDate not supplied

Prostaglandins and otitis media: studies in the chinchilla.

Prostaglandins (PG) are naturally occurring, cyclic, unsaturated fatty acids that possess a wide range of potent biologic activities. Prostaglandins have been found in human middle ear effusions and may have implications for understanding the inflammation and, possibly, the bone resorption seen in chronic otitis media. In the study presented, PGs were measured by radioimmuno-assay in middle ear effusions from experimentally induced serous and purulent otitis media in chinchillas. The ability of chinchilla middle ear mucosa to synthesize PGs from 14C-arachidonic acid was also demonstrated. The authors suggest an active role for PGs in the inflammation and the bone resorption seen in otitis media.

Acid Phosphatase↗