1. In vitro,
Ro 19-3704, a structurally related antagonist of
platelet-activating factor (Paf) inhibited selectively rabbit platelet aggregation. In vivo, administered intravenously, it inhibited bronchoconstriction,
leukopenia,
thrombocytopenia and the accompanying accumulation of platelet aggregates in guinea-pig lung microvessels induced by i.v. Paf. Administered by
aerosol,
Ro 19-3704 failed to inhibit bronchoconstriction,
thrombocytopenia or
leukopenia due to i.v. Paf. 2. Bronchoconstriction induced by Paf, in
aerosol form, was blocked by
Ro 19-3704 administered by the i.v. or
aerosol route, which suggests that it interacts with pulmonary cells responsible for bronchoconstriction. 3.
Ro 19-3704 has
free radical scavenging properties, since it inhibited the production of
superoxide anions by macrophages stimulated by Paf and by
N-formyl-methionyl-leucyl-phenylalanine (FMLP). Ro 18-7715, another Paf antagonist and analogue of
Ro 19-3704, failed to inhibit the production of
superoxide anions by macrophages stimulated by FMLP at concentrations which were effective against Paf. 4. Administered intravenously,
Ro 19-3704 failed to block bronchoconstriction induced by an i.v. injection of
ovalbumin to guinea-pigs passively sensitized with anti-
ovalbumin antiserum. Passive pulmonary
anaphylaxis due to an
aerosol of
ovalbumin was blocked by i.v.
Ro 19-3704.