The isolated human umbilical vein is a robust contractile bioassay for ligands of the bradykinin (BK) B
2 receptor (B
2R), also extendable to B
1 receptor (B
1R) pharmacology. We hypothesized that, as a freshly isolated vessel, it also contains traces of
plasma proteins that may confer responses to exogenous proteases via the formation of kinins.
Main methods
Rings of human umbilical veins were mounted in organ baths containing Krebs buffer maintained at 37 °C and purified proteases were introduced in the bathing fluid along with additional drugs/proteins that permit mechanistic analysis of effects.
Key findings
The previously described contractile response to human recombinant tissue kallikrein (KLK-1, 1–10 nM) is not influenced by metabolic inhibitors, suggesting its dependence on a preexisting reservoir of low molecular weight-kininogen (LK). Active plasma kallikrein (apK, ≤ 5 nM) was inactive in fresh tissues, unless high molecular weight-kininogen (HK, 39–197 nM) replenishment was applied. The effects of KLK-1 and HK + apK are abolished by pretreating tissues with icatibant, but not with tranexamic acid. C1-esterase inhibitor inhibited only HK + apK. Purified plasmin and neutrophil proteinase-3 produced small contractions in the presence of HK only, and tissue plasminogen activator, none. B1R stimulation was pharmacologically evidenced in response to KLK-1 if LK was supplied.
Significance
The pharmacology of KLK-1 and HK + apK in the human isolated umbilical vein is essentially based on the activity of locally generated kinins and this assay models the inhibitory action of some therapeutic agents active in angioedema states. Proteases that indirectly generate kinins have little activity in the system.
