Involvement of histamine in vascular permeability increase of the rat pleurisy induced by phorbol myristate acetate.

Rat pleurisy was induced by an intrapleural injection of 1 nmol (0.1 ml) of phorbol myristate acetate (PMA). Accumulation of pleural fluid peaked at a volume of 1 ml at 1 hr, and exudation rate peaked at 30 min when measured by the amount of dye leaked into the pleural cavity during 20 min. Histamine contents decreased in the pleural cell pellets markedly at 30 min and increased in the supernatant fluid simultaneously, reflecting histamine release that occurred in 30 min after PMA. Pretreatment with mepyramine maleate or methysergide 30 min prior to the PMA-injection suppressed the fluid volume significantly. The result indicates that there are involvements of 5-hydroxytryptamine and the H1-receptor of histamine in the vascular permeability increase at the early stage of PMA-pleurisy.