A SALIVARY VASODILATOR IN THE BLOODSUCKING BUG, RHODNIUS-PROLIXUS

1. Salivary gland homogenates of the blood-sucking bug, Rhodnius prolixus induced transient, dose-dependent relaxation of rabbit aortic preparations pre-constricted with 200 ng ml-1 noradrenaline, 1 μg ml-1 histamine or 20 ng ml-1 angiotensin II. Such relaxations were less marked when the aorta was constricted by 60 mM KCl. These effects were observed with as little as 0.2 μg ml-1 of crude salivary gland protein. 2. The vasodilator effect was endothelium-independent, abolished by 50 μM hydroquinone or 50 μM methylene blue, and potentiated by 30 u ml-1 superoxide dismutase. 3. Salivary homogenates generated a coloured compound when reacted with sulfanilic acid in the presence of N-(1-naphtyl)-ethylediamine, indicating the presence of reactive nitrogen groups, equivalent to 35 ± 3 ng of sodium nitrite per pair of glands. 4. Molecular sieving high performance liquid chromatography of salivary gland homogenates generated a single peak of vasorelaxant activity which coincided with the presence of platelet antiaggregating and spasmolytic (guinea-pig ileum contracted with histamine) activities, as well as with reactive nitrogen groups. 5. It is concluded that a protein of molecular weight 16,500 daltons in the salivary glands of R. prolixus contains reactive nitrogen groups which assist the bug during a blood meal. It is suggested that saliva of blood sucking arthropods is a natural resource of novel pharmacological activities.