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Biomedical subjects

D E MacIntyre

Publications and source records attributed to D E MacIntyre.

At least 91 records · Page 5Linked to original sources
PubMed1978

Malonaldehyde formation in intact platelets is catalysed by thromboxane synthase.

Imidazole and compound L8027 (selective inhibitors of thromboxane synthase) produced parallel inhibition of malonaldehyde and thromboxane B2 secretion induced by collagen or thrombin in gel-filtered suspensions of human platelets. Comparing the effects of these inhibitors and aspirin on secretion of granule constituents indicated that platelet degranulation depends mainly on thromboxane production; prostaglandin endoperoxides contributed little.

Blood Platelets↗
PubMed1978

Prostaglandin receptors on human platelets. Structure-activity relationships of stimulatory prostaglandins.

1. Synthetic analogues of prostaglandins E2 or F2a (monocyclic bisenoic prostaglandins), like the endogenous prostaglandin endoperoxides (prostaglandins G2 and H2) from platelets, and like synthetic analogues of prostaglandin H2 (bicyclic bisenoic prostaglandins), can induce aggregation of human platelets, although prostaglandins E2 and F2a themselves are inactive. 2. All the prostanoid compounds that induce platelet aggregation release 5-hydroxytryptamine from platelet dense bodies, but do not release beta-N-acetylglucosaminidase from lysosomal granules. Arachidonic acid evokes a similar response. 3. All endoperoxide analogues tested (bicyclic compounds) were powerful platelet stimulants, and all active compounds (whether mono- or bi-cyclid) apparently acted via the same receptor as the endogenous prostaglandin endoperoxides. 4. The nature and stereospecificity of substituents at positions 11 and 15 (or 16) on prostaglandin E2 are critical determinants for platelet-stimulating activity: deoxy substitution at position 11 plus methylation at position 15 (or 16) produces a potent stimulant, particularly if the groups around C-15 are in the S configuration. 5. The effects of these structural modifications are apparently due to, at least in part, a change in side-chain conformation.

Adenosine Diphosphate↗
PubMed1977

Aspirin at therapeutic concentrations does not affect 5-hydroxytryptamine uptake by platelets.

Aspirin at therapeutic concentrations does not inhibit the uptake of 5-hydroxytryptamine (5-HT) by blood platelets nor induce release of 5-HT from platelets, although platelet aggregation responses to collagen and arachidonic acid (which are dependent on platelet prostaglandin synthesis) are abolished. This does not support an earlier claim that aspirin's effects on platelet function include inhibition of 5-HT transport.

Aspirin↗
PubMed1977

Endotoxin-induced platelet aggregation and secretion. I. Morphological changes and pharmacological effects.

Endotoxin lipopolysaccharide (LPS) from Acinetobacter 199A induced aggregation of blood platelets from immune adherence-positive species (rat, rabbit) but not from immune adherence-negative species such as pig and man. Aggregation occurred in 2 phases: the first was not accompanied by secretion of platelet constituents, was apparently a consequence of C3 activation, and was selectively inhibited by EGTA. The second phase of aggregation was associated with secretion of platelet granule contents, and with a lesser amount of cytoplasmic leakage. Secondary aggregation was abolished by the sulphydryl alkylating agent N-ethylmaleimide, and by agents which increased the level of cyclic AMP in platelets, such as prostaglandin E1 (a stimulator of adenylate cyclase) and methyl xanthines (inhibitors of phosphodiesterase). Secondary aggregation was partly inhibited by agents which block platelet prostaglandin biosynthesis (e.g. aspirin, indomethacin). Primary aggregation was unaffected by these inhibitors at concentrations which blocked secondary aggregation.

Acetylglucosaminidase↗
PubMed1977

Endotoxin-induced platelet aggregation and secretion. II. Changes in plasma membrane proteins.

Responses of blood platelets to bacterial endotoxin lipopolysaccharide (LPS) have been correlated with changes in the molecular organization and composition of the platelet plasma membrane proteins. Binding of LPS, which occurred in the absence of Ca2+, was distinguished from platelet aggregation and degranulation, which required Ca2+ and plasma proteins. Changes in membrane organization were detected by double-labelling with [125I] and [131I] iodide, mediated by lactoperoxidase and hydrogen peroxide. Changes in total membrane composition were detected by gel electrophoresis of isolated membranes. Binding of LPS was associated with increased accessibility of a protein of mol. wt. 80000 to iodination. After aggregation and degranulation there was, in addition, increased accessibility of proteins of mol. wt. 68000 and 48000. Isolated membranes from LPS-stimulated platelets contained more of a protein of mol. wt. 200000 and less of a protein of mol. wt. 220000 than control membranes prepared from unstimulated platelets in the presence of cAMP and aminophylline. The relationship of the modified plasma membrane proteins to the contractile proteins of the platelet and their possible redistribution in the cell during aggregation and secretion is discussed.

Acinetobacter↗