The antiserotonin and antihistamine activities of salivary secretion of Rhodnius prolixus

The antiserotonin and antihistamine activities of Rhodnius prolixus salivary secretion were studied using the rat uterus and the guinea pig ileum preparations. Serotonin antagonism was not competitive and the salivary secretion dose which abolished a half-maximal uterine contraction was 13 ± 2 (S.E.) μg protein/ml (n = 9). No inhibition was seen for the acetylcholine and bradikinin contractures. On the other hand, the observed antihistamine activity was typically competitive. The mean concentration of Rhodnius salivary secretion of 14 ± 2 (S.E.) μg protein/ml (n = 9) reduced the effect of histamine to that of a half dose. Specificity was demonstrated when testing salivary secretion in the acetylcholine and BaCl₂-induced guinea pig ileum contractures. In both antagonisms, no preincubation was needed for the full expression of the inhibitory effect, which did not persist after washing the preparation. The presence of enzymes that could be degrading the amines was excluded.Susceptibility to trypsin and heat treatments as well as the behaviour of the principles on gel filtration and preparative agarose electrophoresis experiments, suggest that the activities reside in the same peptide molecule with an apparent molecular weight of 39,000 daltons.