1 The thromboxane-sensitive contractile systems in spirally-cut preparations of the rabbit aorta, dog saphenous vein and guinea-pig trachea have been compared. The full or partial agonist activities of a range of bicyclic ring analogues were found to be remarkably similar on the three preparations. In addition, EP 045, a prostanoid with a phenylsemicarbazone w-chain, blocked the action of both thromboxane A2 (TXA2) and the bicyclic ring analogues. Using 11,9-epoxymethano prostaglandin H2 as the agonist, linear Schild plots with slopes close to unity were obtained on each preparation; this suggests a competitive type of antagonism. 2 Analogues of prostaglandin D2 (PGD2), PGE2 and PGF2a also contracted the three smooth muscle preparations; those analogues containing a 16-p-halophenoxy residue were highly active. On the rabbit aorta, EP 045 completely blocked the contractile actions of these agonists, perhaps indicating a single type of prostanoid receptor in this tissue. On the dog saphenous vein PGD2, PGE2 and 15-methyl PGE2 exhibited relaxant activity when the tissue was partially contracted with either a thromboxane agonist or noradrenaline. On the guinea-pig trachea 16,16-dimethyl PGE2 and the 16-p-chlorophenoxy analogue of PGE2 were potent contractile agents whose action was not blocked by EP045. PGE2 and 15-methylPGE2 showed similar properties but exhibited relaxant activity with increasing concentrations in the organ bath. Our results indicate the presence of three types of prostanoid receptors in the guinea-pig trachea: thromboxane-and PGE-sensitive systems mediating contraction and a PGE-sensitive system mediating relaxation. 3 The similarity of the thromboxane-sensitive systems in the three smooth muscle preparations is discussed with particular reference to the differences in the equilibrium dissociation constants for EP 045.

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The inhibitory effects of three prostanoid analogues. EP 045, EP 092 and pinane thromboxane A2 (PTA2), on the aggregation of human platelets in vitro have been investigated. 2 In diluted platelet-rich plasma (PRP), EP 045 (20 pM) and EP 092 (1 fiM) completely inhibited irreversible aggregation responses to thromboxane A2 (TXA2), prostaglandin H2 (PGH2) and five chemically stable thromboxane mimetics, including 11 ,9-epoxymethano-PGH2 and 9,11 -azo-PGH2. Reversible aggregation produced by the prostanoid analogue, CTA2, was also inhibited. The block of the stable agonist action was surmountable. In plasma-free platelet suspensions EP 045 and EP 092 were more potent antagonists. Schild analysis indicated a competitive type of antagonism for EP 045 (affinity constant of 1.1 x I 0 M-'); the nature of the EP 092 block is not clear. 3 Primary aggregation waves induced by ADP, platelet activating factor (Paf) and adrenaline were unaffected by EP 045 and EP 092, whereas the corresponding second phases of aggregation were suppressed. Aggregation and 5-hydroxytryptamine (5-HT) release induced by either PGH2 or 11,9-epoxymethano-PGH2 were inhibited in a parallel manner by EP 045. Inhibition of thromboxane biosynthesis is not involved in these effects. 4 EP 045 and EP 092 did not raise adenosine 3': 5'-cyclic monophosphate (cyclic AMP) levels in the platelet suspensions. 5 In plasma-free platelet suspensions PTA2 produced a shape change response which could be blocked by EP 045. PTA2, therefore, has a thromboxane-like agonist action. The block of the aggregatory action of 11 ,9-epoxymethano-PGH2 by PTA2 appears to be mainly due to competition at the thromboxane receptor. However, PTA2 produced a slight rise in cyclic AMP levels; this could be due to a very weak stimulant action on either PGI2 or PGD2 receptors present in the human platelet. Functional antagonism by PTA2 may therefore augment its thromboxane receptor blocking activity. 6 The results are discussed in terms of (a) the specificity of antagonism produced by EP 045, EP 092 and PTA2, (b) the validity of affinity constant determinations for receptor antagonists when aggregation is the biological response, and (c) the characteristics of the human platelet thromboxane receptor in comparison with those of thromboxane receptors in smooth muscle.

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Intense green emission was observed at room temperature from the 4S3/2 level of Er3+ doped in a multielement oxide glass when its 4I9/2 level was resonantly excited with a near-infrared laser beam of 797 nm. Our studies indicate that energy transfer and excited state absorption are responsible for the generation of upconverted green emission from the sample. The upconversion efficiency is found to be 0.14%.

Competition and consumer brand attitudes make introducing a new brand risky and very expensive, increasing the attractiveness of brand extensions. Brand extension research has established that original brand quality perceptions, product category fit, consumer perceptions of the product category complementarity and substitutability, plus the transferability of design and manufacturing capability significantly influence extension attitude formation. However, these studies fail to differentiate between brand types and have aggregated out category effects. Using a national survey we show that brand type (prestige, functional) and extension category are important variables in consumer brand extension attitude formation. Perceived quality influences functional brands more than prestige brands as prestige brand attitudes assume quality. Functional brands experience less dilution than prestige brands, implying less risk and greater expandability than argued by previous authors.

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