The aim of this study was to clarify the role of endogenous bradykinin (BK) in the hypotensive response induced by lipopolysaccharide (LPS) by comparing the degree of hypotension caused by LPS in a strain of specific pathogen-free (SPF) Brown Norway (B/N), kininogen-deficient mutant Katholiek rats with that of B/N normal Kitasato rats. 2. The dose-dependent hypotensive responses caused by intravenous injection of BK (1-100 nmol kg-1) or platelet-activating factor (PAF, 0.003-1 microgram kg-1), were not different in the two strains of rats used. However, there was a strong difference in the hypotensive response induced by LPS in kininogen-deficient and normal rats; in normal rats the hypotensive response was composed of two phases (15 min and 70-80 min after LPS injection), but in kininogen-deficient rats LPS caused a delayed (second phase), but not an acute (first phase) hypotension. 3. We demonstrate that Hoe 140 (1 mg kg-1, i.v.) is a potent, selective, and long-lasting antagonist of the hypotensive effects of BK. Hoe 140 diminished the hypotension caused by LPS in normal rats to the level observed in kininogen-deficient rats, but had no effect on the hypotension caused by LPS in kininogen-deficient rats. 4. TCV309 (0.1 mg kg-1, i.v.) selectively inhibited the hypotension caused by repetitive injection of PAF for up to 180 min. Pretreatment with TCV309 caused a near complete inhibition of the LPS-induced hypotension in kininogen-deficient and normal B/N rats. 5. In the normal rats, dexamethasone (0.5 mg kg-1, i.p.) inhibited the second phase of the hypotension induced by LPS, but not the first phase of the hypotension. 6. A small amount of BK (0.1 nmol kg-1) potentiated the hypotensive action of PAF (0.01 microg kg-1),when they were injected simultaneously.7. In conclusion, we demonstrate that formation of endogenous BK contributes primarily to the acute,but not to the delayed hypotension afforded by endotoxin in the rat. In contrast, formation of endogenous PAF contributes to both the acute and the delayed hypotension afforded by endotoxin in vivo.
