The kinin system: its relation to blood coagulation, fibrinolysis and the formed elements of the blood

The effects of a kinin antagonist on changes in lung function and plasma extravasation into the airways following challenge of sensitized guinea-pigs

BACKGROUND

It has been suggested that kinins may play a role in allergic pathophysiology of the airways, contributing to bronchoconstriction and oedema formation. Raised levels of kinin generating enzymes and kinins are found in the airways during allergic responses.

OBJECTIVE

Using an in vivo animal model of allergen induced increase in airways resistance we investigated the effects of the bradykinin antagonist Hoe 140, in order to assess the possible contribution of kinins to this response.

METHODS

Guinea-pigs were sensitized and challenged with ovalbumin (OA) or saline via the endotracheal route and the resulting increase in airways resistance was measured by whole body plethysmography. At 240 min after challenge, bronchoalveolar lavage fluid (BALF) was taken and albumin content and kallikrein-like activity determined by rocket immunoelectrophoresis and use of artificial substrates respectively. Pretreatment of animals with the bradykinin antagonist Hoe 140 at 6.7, 20 or 66.7 nmol/kg or aprotinin (46,000 kallikrein inhibitor units/kg) was by i.p. injection 10 min before challenge.

RESULTS

Pre-treatment with Hoe 140 dose dependently attenuated the increase in airways resistance following allergen challenge. Kallikrein-like activity and albumin in BALF were unaltered. Aprotinin reduced the kallikrein-like activity in BALF but did not alter airways resistance.

CONCLUSION

Kinins may contribute to a significant part of allergen-induced airways resistance increase in this model but not via an effect on plasma extravasation.

Characterization of Gaddum's substance R

1. When the isolated small intestine of the rat is perfused via the mesenteric artery, an oxytocic principle (Gaddum's substance R) is released which is detectable in the perfusate after 30 min and is present in samples collected 8 h later. 2. The oxytocic activity of substance R is lost after boiling but is unaffected by treatment with thioglycolate. Furthermore, atropine, methysergide and indomethacin failed to antagonize uterine contractions to substance R. 3. Neither substance R nor urinary kallikrein alone induce a contraction of the guinea-pig isolated ileum. However, in the presence of kininogen both substance R and urinary kallikrein produce a slow and prolonged contraction of the guinea-pig ileum. 4. The oxytocic and kininogenase properties of both substance R and urinary kallikrein are inhibited by Trasylol. 5. Soy bean trypsin inhibitor (SBTI) selectively inhibited both the oxytocic and the kininogenase activities of substance R but not those of urinary kallikrein. 6. Gel filtration of substance R resolved a single peak of oxytocic activity with an estimated molecular weight of 40 kDa. 7. We conclude that substance R is a kininogenase enzyme which may be distinguished from plasma kallikrein by its molecular weight and from urinary kallikrein by its susceptibility to SBTI. The exact nature of this enzyme remains to be elucidated.

Purification of a proteinase inhibitor from bovine serum with C1-inhibitor activity

This report describes the purification of a novel proteinase inhibitor from bovine serum. This protein was purified to apparent homogeneity employing affinity binding to sulfated dextran and precipitation by ammonium sulfate, followed by sequential chromatography on DEAE-cellulose, heparin-Sepharose and Sephacryl S-200. Quantitative enzyme-linked immunosorbent assays revealed that the concentration of this inhibitor is approximately 3 microM in bovine serum. The inhibitor is a single polypeptide chain with an estimated Mr of 83,000 as determined by SDS-polyacrylamide gel electrophoresis. An aspartic acid was found at the amino terminus of the protein; N-terminal amino acid sequence data indicated that there was no significant homology with other reported amino acid sequences. This bovine inhibitor covalently complexed the human proteinases C1-r, C1-s, factor XIIa and plasma kallikrein, which are also complexed and inactivated by human C1-inhibitor. In addition, the bovine inhibitor complexed and inactivated bovine chymotrypsin, a feature which functionally distinguishes it from human C1-inhibitor. Although the bovine inhibitor appears functionally very similar to C1-inhibitor, we found no evidence for structural homology with the human counterpart.

Vasoactive Peptides and Regulation of Hemodynamics in Different Functional States of the Organism

It is important to emphasize that the biochemical systems participating in humoral hemodynamic regulation may function at any level of the circulatory homeostasis: in the blood as a biological fluid constantly circulating along the vessels, at the microcirculatory bed where the exchange with tissues is realized, on the tonic activity of the resistive and capacitance vessels, defining the systemic blood pressure rate and organ redistribution, or, finally, on the main motive force of the blood, the heart. The interrelations of some molecular factors form the biochemical basis for the interaction of the main humoral systems. These factors are kallikrein for kinins and converting enzyme for the renin-angiotensin system, 9-ketoreductase and phospholipase for kinin and prostaglandin systems, and Hageman factors for coagulation, fibrinolysis, and kininogenesis systems. This main scheme includes "functional" connections, which are defined by a physiological interaction, and those between the central and peripheral nervous systems. We may, evidently, postulate an important biological regularity of a multi-functional participation of the same physiologically active factors in maintaining circulatory homeostasis. On the other hand, we have to emphasize the functional unity and joint correlating actions of different biochemical blood systems.

On the biological role of a proteolytic-enzyme inhibitor from the ectoparasitic tick Boophilus microplus

The tick Boophilus microplus contains a protein that inhibits a range of proteolytic enzymes. Variations in the concentration of this protein throughtout the life cycle were followed by measuring simultaneously the inhibition of trypsin and chymotrypsin and reaction with an antiserum to the purified inhibitor. The protein is present in large amounts in eggs and in unfed larvae, but its concentration falls very rapidly after the start of the parasitic stage of the life cycle. This, together with previous evidence, suggests that the inhibitor is important both in eggs and in the initial establishment of the parasite on its host. The activity of the protein towards several enzymes has been measured as an indication of its possible function. Bovine trypsin, chymotrypsin and plasmin and pig pancreatic kallikrein are all inhibited. The protein also affects the blood-coagulation system at several points, since it prolongs both activated-partial-thromboplastin time and prothrombin time. It inhibits the complement-dependent lysis of erythrocytes, but is without significant effect on mitogen-induced lymphocyte stimulation. Thus the inhibitor could have several effects on the host that would be beneficial to the parasite.

Similarity between a kininogenase (kallikrein) from human large intestine and human urinary kallikrein

A human colon kininogenase (kallikrein) was isolated by gel filtration on Sephacryl S-200 and affinity chromatography on Trasylolbound Sepharose, yielding a material with a specific activity of 1.3 U/mg (substrate: AcPheArgOEt). The molecular weight of the enzyme as estimated by gel filtration is approximately 70 000. After reduction with mercaptoethanol two bands were obtained in dodecyl sulfate eletrophoresis with molecular weights of 27 000 and 70 000. The bimolecular velocity constant for the inhibition by diisopropyl fluorophosphate was determined as 4 l x mol-1 x min-1. The preparation was characterized by immunological and enzymatic methods. Using the radioimmumoassay for human urinary kallikrein cross-reactivity and parallel binding curves were obtained. Kinin liberation from human high Mr-kininogen was totally inhibited by antibodies directed against human urinary kallikrein. Trasylol and diisopropyl fluorophosphate, but not by antibodies directed against human trypsin and plasma kallikrein. The effect on dog blood pressure was comparable to that obtained with human urinary kallikrein. The amino acid composition of human large intestine kallikrein is very similar to that of human urinary kallikrein.