In conditions like allergic asthma, platelets participate by acting as inflammatory cells, by releasing mediators, spasmogens
and/or by interacting with other inflammatory cell types.
5-Lipoxygenase (5-LOX) catalyzes the first step in the oxygenation of arachidonic acid, thus leading to the production of biologically active spasmogens
, compounds such as leukotrienes and 5-hydroxy-eicosatetraenoic acid.
Asthmatic airway obstruction is induced by various bronchoconstricting factors (like allergens, pharmacological spasmogens
, physical stimuli, infectious disease state) and is inhibited by NO (130).
Human asthma is characterized and its severity is diagnosed by heightened airway reactivity to varying concentrations of nonspecific bronchoconstrictors or spasmogens
such as methacholine.
Erythrocytes trapped in the subarachnoid cisterns slowly hemolyze and release potent spasmogens
such as oxybemoglobin. The result is severe, sustained smooth muscle contraction in the cerebral arterial wall.
The antipasmodic activity of 2.5 and 10.0 ml/l of alcoholic extracts of Melissa officinalis, Rosmarinus officinalis, Mentha piperita, Matricaria chamomilla, Foeniculum vulgare, Carum carvi and Citrus aurantium prepared from 1 part of the plant and 3.5 parts of ethanol (31% w/w) was tested employing the guinea pig ileum and using acethylcholine and histamine as spasmogens
(Forster et al., 1980).
Interestingly, EOO[G.sub.8] and EOO[G.sub.12] were significantly less potent in relaxing Ach--than high potassium-induced tone, which may reflect the transduction mechanisms utilized by the respective spasmogens
. In guinea-pig ileum the contraction elicited by high potassium is due to influx of extracellular calcium into the muscle cell via voltage-dependent calcium channels (Bolton, 1979), and was completely inhibited by diltiazem, whereas ACh-induced responses may instead involve activation of non-selective cation channels (Chen et al., 1993).