RESUMEN
General characteristics of waxes, adhesives and lubricants as well as the recent fundamental investigations on their physical and mechanical behaviour are introduced. The current R&D status for new type/generation of waxes, adhesives and lubricants from natural products is reviewed, with an emphasis on their tribological applications. In particular, some crucial issues and challenges relating to technological improvement and materials development are discussed. Based on the current predicted shortage of energy resources and environmental concerns, prospective research on the development of green waxes, adhesives and lubricants is suggested.
RESUMEN
The effects of tetrandrine, a Ca2+ antagonist of bis-benzylisoquinoline alkaloid origin, on endothelium-dependent and -independent vascular responsiveness were investigated in perfused rat mesenteric artery. In endothelium-intact preparations pre-contracted with 3 microM phenylephrine and fully relaxed by 0.3 microM acetylcholine tetrandrine caused a rapid transient contraction. In endothelium-denuded preparations, tetrandrine caused only vasorelaxation of phenylephrine-contraction. The biphasic effect of tetrandrine in acetylcholine-relaxed preparations could also be mimicked by sequential applications of atropine/tetrandrine or N(G)-nitro-L-arginine-methylester (L-NAME)/tetrandrine, but atropine or L-NAME alone caused only vasoconstriction. This tetrandrine-induced transient vasoconstriction was also observed in preparations relaxed with ATP, histamine or thapsigargin (TSG), but not those relaxed with A23187, sodium nitroprusside or nifedipine. The present results suggest that tetrandrine, in addition to its known inhibitory effects on vascular smooth muscle by virtue of its Ca2+ antagonistic actions, also inhibits NO production by the endothelial cells possibly by blockade of Ca2+ release-activated Ca2+ channels.
