Salivary gland extracts of several Simulium spp. were shown to contain
vasodilative activity as measured by the rapid and persistent inducti
on of erythema in response to intradermal injection into rabbit skin.
Total salivary gland activities were approximately equal for S. vittat
um, S. metallicum, S. bivittatum, and S. argus (titers of 0.03-0.02 pa
irs of gland). Total gland activity in the highly anthropophilic speci
es S. ochraceum, however, was an order of magnitude greater, with eryt
hema produced by as little as 0.002 pairs of glands. Tests for physica
l stability of the activities from two species (S. vittatum and S. och
raceum) indicated that the vasodilators were proteinaceous and heat st
able. A two-step, reversed-phase high-performance liquid chromatograph
y (HPLC) procedure was developed that isolated both activities with si
milar elution patterns. Homogeneity of the purified protein from S. vi
ttatum was confirmed by capillary gel electrophoresis. Electrospray io
nization mass spectroscopy of the S. vittatum protein detected a mass
of 15,351 daltons. Similarity in elution times of the proteins from a
TSK HPLC column predict some structural similarities between the S. vi
ttatum and S. ochraceum vasodilator proteins.