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The monospecific fern genus Cystodium (Cystodiaceae; Polypodiales) occurs exclusively in the tropical forests of the Malay Archipelago, the Admiralty Islands, the Louisiade Archipelago, and the Solomon Islands. Divergence time estimates suggest that the genus originated in the Mesozoic; however, fossil evidence to validate this suggestion has been lacking. Amber from Myanmar (Burmese amber) is an important source of new information on the diversity of vascular cryptogams in the Cretaceous. This paper describes the fossil taxon Cystodium sorbifolioides nov. sp. based on a fragment of a fertile leaf preserved in Burmese amber that represents the first fossil evidence of the family Cystodiaceae. Cystodium sorbifolioides is used to obtain a minimum age estimate for the Cystodiaceae and the closely related, monogeneric Lonchitidaceae and Lindsaeaceae. The fossil strengthens the hypothesis that the forest ecosystems of Malesia and Melanesia represent refugia for many tropical plant lineages that originated in the Cretaceous.

The abilities of WY-50,295 tromethamine, a 5-lipoxygenase inhibitor, to inhibit antigen-induced leukotriene (LT) release from guinea pig lung fragments, and to prevent LTD4 or antigen-induced contraction of isolated guinea pig tracheal muscle were compared with the activities of zileuton and MK-886 (two selective 5-lipoxygenase inhibitors), and LY171883 (a LTD4 receptor antagonist). In fragmented guinea pig lung, WY-50,295 tromethamine inhibited antigen-induced LT release with an IC50 of 0.63 microM, and was 4.6- and 5.2-fold more potent than zileuton and MK-886, respectively. WY-50,295 tromethamine differed from these 5-lipoxygenase inhibitors, however, in that WY-50,295 tromethamine competitively antagonized LTD4-induced tracheal contractions (pA2 = 6.06) at concentrations that inhibited LT release. LY171883 was an effective LTD4 receptor antagonist (pA2 = 6.96), that only inhibited antigen-induced LT release at higher concentrations (IC50 = 7.9 microM). WY-50,295 tromethamine almost completely inhibited antigen-induced leukotriene-dependent tracheal contractions, whereas high concentrations of zileuton, MK-886, or LY171883 produced only partial inhibition. This partial inhibition was likely to result from 'breakthrough' 5-lipoxygenase activity, because combinations of zileuton plus MK-886 or zileuton plus LY171883, were more effective than zileuton, MK-886, or LY171883 alone. The greater efficacy of WY-50,295 tromethamine in the antigen-challenged guinea pig trachea is likely to result from its combined abilities to prevent LT biosynthesis and block LTD4 receptors.