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PubMed1984

[Role of bradykinin in hypotension induced by the active factor derived from factor XII].

The active fragment derived from factor XII (factor XIIf) was purified from human plasma and administered intravenously to normotensive conscious rats. Factor XIIf-mediated hypotension was dose-dependent and augmented by pretreatment with captopril, an inhibitor of the angiotensin I- and bradykinin-processing enzyme. In contrast, factor XIIf-induced hypotension was not enhanced by blockade of the renin-angiotensin system by saralasin, a competitive antagonist of angiotensin II at the vascular receptor level. These results suggest that factor XIIf-mediated hypotension is due to the formation of bradykinin.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1983

Studies of the kallikrein-kinin system in patients with sickle cell anemia.

Eight patients with sickle cell anemia (SS hemoglobin) were found to have decreased plasma levels of prekallikrein compared to normal control subjects or patients with other types of anemia. The prekallikrein levels in the patients with sickle cell anemia were found to decrease further during a sickle cell crisis. These results suggest that components of the kallikrein-kinin system are profoundly affected in patients with sickle cell anemia, and during crises may play a role in the clinical presentation of patients.

Adolescent↗
PubMed1983

The role of prekallikrein and high-molecular-weight kininogen in the contact activation of Hageman factor (factor XII) by sulfatides and other agents.

Hageman factor (HF, factor XII), adsorbed to negatively charged agents, is transformed to an activated state in which it initiates reactions of the intrinsic pathway of thrombin formation by activating plasma thromboplastin antecedent (PTA, factor XI). High-molecular-weight kininogen (HMWK, Fitzgerald factor) and plasma prekallikrein accelerate these early steps in the clotting process. Questions have been raised about the role of HMWK in the activation of Hageman factor by surfaces. In the present studies, we report that the activation of purified human HF by sulfatides, ellagic acid, kaolin, or glass occurred in the absence of HMWK. Indeed, small amounts of HMWK inhibited activation of HF by ellagic acid. Physiological concentration of HMWK had little or no influence on the activation of HF by sulfatides, kaolin, or glass, but higher concentrations (3 to 6 times more) showed the same inhibitory effect as after activation by ellagic acid. This inhibitory property of HMWK may be attributed to competitive binding of HF and HMWK on the surface of the activating agents. In fact, when HF was added to kaolin or glass that had been incubated with HMWK and then washed, the inhibitory effect persisted, indicating HMWK that was bound to the surface blocked activation of HF. Studies with 125I-HF and 125I-HMWK supported this interpretation. Plasma prekallikrein accelerated activation of the amidolytic properties of HF by sulfatides, kaolin, or glass but did not influence activation of HF by ellagic acid. In the presence of plasma kallikrein, HMWK at moderate concentrations slightly accelerated the rate of activation of HF by activating agents other than ellagic acid. Higher concentrations of HMWK counteracted both the accelerating effect of prekallikrein and the inhibitory effect observed when HF was incubated with an excess of kaolin. These experiments, then, support the view that the procoagulant function of HMWK is localized to a point subsequent to the activation of HF.

Ellagic Acid↗
PubMed1980

Prekallikrein activator levels and side effects with human albumin preparations.

Recently the question has been raised whether the presence of prekallikrein activator (PKA) in human blood products for i.v. application could possibly cause adverse reactions in the recipient as observed now and then. Up to now a correlation between both properties is far from being established, even though in the U.S. there has been extensive discussion over some PPL batches containing elevated amounts of PKA, presumed to be causally related to an increased frequency of side reactions. As has been demonstrated in the past through wide clinical experience, human albumin is an exceptionally safe blood product. If at all, side effects sometimes seem to occur related to certain individual lots, the reason for which is still unrevealed. In the pursuit of eventually finding some association between PKA levels in and side reactions with albumin, we performed PKA measurements on a panel of commercial human albumin batches, a few of which had been reported occasionally to cause adverse reactions. The assay procedure was essentially that published (3). BOB PKA reference No 1 was included as a standard. PKA was detected in moderate amounts in huge series of albumin batches without any reported side reactions. We conclude, therefore, that PKA levels in the range of trace amounts cannot be related to side reactions with human albumin preparations.

Esterases↗
PubMed1982

Enzymatic activities of activated and zymogen forms of human Hageman factor (factor XII).

Pro-Phe-Arg chloromethylketone (PPACMK) at 5.26 microM inactivated the amidolytic activity of native human Hageman factor with an apparent first-order rate constant of 0.75 min-1. The activated forms of Hageman factor, Hfa and HFf, were also inactivated by PPACMK with rate constants 0.82 and 0.72 min-1. These numbers indicate that the activity detectable in native Hageman factor is due to contamination with activated species. Uncleaved Hageman factor reacts slowly with 40 mM diisopropyl fluorophosphate with concomitant loss of its procoagulant activity. Incubation of native Hageman factor with PPACMK does not destroy its procoagulant activity, even in the presence of the activator dextran sulphate, but PPACMK inhibits autoactivation of Hageman factor, suggesting that no active site is formed in uncleaved, surface-bound Hageman factor. The activation of prekallikrein by Hageman factor under initial-rate conditions occurs after a lag and is prevented by an inhibitor of Hageman factor from corn. The kinetics of prekallikrein activation and the effects of inhibitors provide evidence that the amidolytic and proteolytic activities of human Hageman factor reside in the activated forms derived by limited proteolysis of the native molecule.

Amides↗
PubMed1982

Bradykinin-mediated hypotension after infusion of plasma-protein fraction.

In patients who required volume expansion during extracorporeal circulation, the plasma bradykinin concentration was monitored simultaneously with the mean arterial pressure during infusion of either albumin solution or PPF. The PKA content of the PPF and the albumin solution was 29 and 3 U/L, respectively, measured spectrophotometrically. In six patients receiving 250 ml of PPF, the mean arterial pressure decreased 22% to 54% within 1.5 min after infusion, whereas the plasma bradykinin concentration, measured by radioimmunoassay, increased significantly (p less than 0.0005) during the first minute. In six patients receiving 250 ml of 4% albumin solution, no blood pressure changes were found, and the plasma bradykinin concentration rose only slightly. In vitro, linear correlation (r = 0.94, p less than 0.0005) was observed between the level of PKA of 26 different lots of PPF and the concentrations of bradykinin that were generated in Hageman factor-deficient plasma after incubation with PPF. It is concluded that the hypotensive reactions observed after PPF infusion during extracorporeal circulation are caused by the PKA-induced bradykinin generation.

Adult↗
PubMed1982

Hypotensive effects of plasma protein fraction. The relation between prekallikrein activator, bradykinin generation, and blood pressure in an animal model.

In a rat model, the relationship between the activity of PKA in human PPFs, the changes in arterial BK concentration, and the changes in blood pressure on infusion of PPF was investigated. The rat was chosen as a model because it is reported to be one of the few animals sensitive to human PKA. However, hypotensive reactions after infusion of human PKA-containing PPF were observed only in the presence of a bradykinin-potentiating peptide (BPP9a). A correlation was found between the PKA content of the rapidly infused PPF, the BK generation in the rat, and the fall in arterial blood pressure. In control experiments, infusions of BK provoKed a similar fall in blood pressure at corresponding BK levels. After neutralization of the PKA activity in the PPF with C1-esterase inhibitor, neither a rise in BK level nor a fall in blood pressure was observed on infusion. We conclude therefore that the hypotensive reactions were caused by PKA-mediated generation of BK.

Animals↗
PubMed1994

A model demonstrating different interactions of human coagulation factor XII (Hageman factor) with the surface at physiological and lower pH.

The surface binding activity of human coagulation factor XII is independent of pH while its proteolytic breakdown decreases considerably on lowering the pH (Samuel, M. and Villanueva, G.B. (1992) Biophysical J. 61, 1895). In the present study we showed that the amidolytic activity of factor XII in the presence of a soluble surface, dextran sulfate (DS500; Mr 500,000) decreases on lowering the pH. Electrophoretic and ultraviolet difference spectral studies indicate that factor XII binding stoichiometry to DS500 is reduced to half at pH 5.3 when compared to that at pH 7.4. A model is presented to show the different interactions of factor XII with DS500 which explains its well known stability at low pH.

Chromogenic Compounds↗