T. Akata et al., HEPARIN PREVENTS THE VASODILATING ACTIONS OF PROTAMINE ON HUMAN SMALLMESENTERIC-ARTERIES, Anesthesia and analgesia, 76(6), 1993, pp. 1213-1221
Despite the wide dinical use of protamine, the precise mechanisms Of i
ts hypotensive effects during reversal of heparin anticoagulation have
not been elucidated fully. We, therefore, investigated the effects of
protamine on isolated human small mesenteric arteries, both in the ab
sence and presence of heparin, employing the isometric tension recordi
ng method. Protamine exerted vasodilating actions in the absence of he
parin: 1) protamine (greater-than-or-equal-to 50 or 150 mug/mL) inhibi
ted (P < 0.05) both norepinephrine (1 muM)- and high K+ (40 mM)-induce
d contractions in the presence of extracellular Ca2+ both in endotheli
um-intact and -denuded tissues; and 2) protamine inhibited (P < 0.05)
norepinephrine (1 muM)-induced, but not caffeine (10 mM)-induced, cont
ractions in the absence of extracellular Ca2+. Such vasodilating actio
ns were blocked almost completely in the presence of heparin. We concl
ude that only protamine, but not a heparin-protamine complex, has a va
sodilating action on the human arteries.