The active site tripeptide arginal inhibitor of
thrombin,
LY287045, was used to study
thrombin-induced aortic relaxation and contraction, two responses that differ both pharmacologically and physiologically. Although
thrombin (10(-7) M) and
trypsin (10(-6) M) were tachyphylactic upon repeated administration,
trypsin contracted the aorta following
thrombin-induced contraction.
LY287045 (10(-7) M) attenuated
thrombin-induced vasorelaxation, but not vasoconstriction with -log K(B) of 8.4.
LY287045 (10(-7) M) also attenuated vasorelaxation, but not vasoconstriction to
trypsin, another
serine-protease with a
thrombin-like catalytic triad, with similar potency (-log K(B) = 8.6) to that for
thrombin. Consistent with these vascular effects,
LY287045 inhibited the
protease activity of both
thrombin and
trypsin. To explore further the selective inhibitory effect of
LY287045 on
protease-induced relaxation, we examined the effect of
LY287045 on the
nitric oxide and
prostacyclin pathways and found that
LY287045 did not alter vascular responses mediated by
nitric oxide or
prostacyclin. Likewise,
LY287045 did not exert a direct inhibitory effect on the relaxant
protease-activated receptor (PAR) since relaxation to the PAR-2-activating
peptide was not blocked. The selective effect of
LY287045 to inhibit only
protease-induced endothelial-dependent relaxation demonstrated that
protease inhibition will not affect all
protease responses equally. Furthermore, increases in
trypsin and
thrombin have been associated with
inflammation and angiogenesis. To the extent that these findings suggest that
LY287045 exhibit dual
protease inhibition of endothelial responses,
LY287045 may have specific utility in hypotensive inflammatory diseases and in
cancer metastases where both
trypsin and
thrombin have been implicated as causative agents.