A salivary vasodilator in the blood‐sucking bug, Rhodnius prolixus

Abstract

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.