Plasma histamine in patients with tropical disorders and acute asthma who exhibit eosinophilia.

The mean venous plasma histamine of 14 patients with eosinophilia was 18.7 nmol/L (range 0-86.4) and significantly higher than that of 4.0 nmol/L for 29 normal subjects [range 0-10.8 (P < 0.01)]. The eosinophilia of schistosomiasis (two patients), strongyloidiasis (one patient), and asthma (four patients) was accompanied by raised plasma histamine concentrations. Normal levels occurred in onchocerciasis (four patients) and in two of three patients with non-specific eosinophilia. Plasma histamine concentrations in the tropical disorders are not thought to have been reported previously. The initial arterial and venous plasma histamine concentrations of 14 acute asthmatics, were significantly positively correlated with the respective arterial (P < 0.01) and venous (P < 0.05) eosinophil counts. The results in acute asthma support the hypothesis that increased plasma histamine may have a role in promoting eosinophil release from the bone-marrow. Eosinophilia is not dependent upon a raised plasma histamine in some disorders, but may be in others, such as schistosomiasis.