Sulphuric esters of polysaccharides as activators of a bradykinin-forming system in plasma.

Abstract

PREVIOUS work1 has shown that intravenous injection of agar, a naturally occurring sulphuric ester of polygalactose, leads to an appreciable reduction in bradykininogen concentration as well as to a significant increase of p-tosylarginine methyl ester (TAMe) esterase activity in the plasma of the rat. Other results indicate that, besides agar, synthetic sulphuric esters of certain polysaccharides are potent activators of the bradykinin forming system in rat or human plasma in vitro. In the experiments demonstrating this activity, 0.2 per cent oxalated plasma was collected, avoiding contact with glass, and treated with 1 mg/ml. of 8-hydroxy quinoline (8HQ), an inhibitor of enzymes which destroy bradykinin2. Kinin formed was assayed on isolated, atropinized guinea-pig ileum which had been treated with antihistamine, using synthetic bradykinin as the standard. Powdered cellulose, glycogen from shellfish, inulin, soluble starch and agar were added to rat plasma, either as such, or after conversion to water soluble sulphuric esters by treatment with chlorosulphonic acid in pyridine3. The effects of carrageenin, a sulphuric ester of polygalactose, extracted from Irish moss, as well as of heparin, were also examined. When incubated at 37° C with rat plasma, all sulphuric ester polysaccharides caused stimulation of smooth muscle equivalent to, on average, 1.0 µg of bradykinin/ml. The active material formed had the characteristics of bradykinin; it was rapidly destroyed by plasma in the absence of 8HQ, as well as by chymotrypsin. Maximum activation was reached 1 min after the addition of 10−4 or 10−5 g of cellulose sulphate to 1 ml. of plasma (Fig. 1). Larger concentrations (10−3 g/ml.) of this activator were less effective during the early phase of the incubation, which suggests an inhibitory effect of excess sulphopolysaccharide on bradykinin production. Ten parts by weight of hexadimethrine bromide, previously shown to inhibit kinin formation4, inactivated one part of cellulose sulphate. None of the non-sulphated, native polysaccharides induced kinin formation; heparin, a sulphated derivative of polyglucosamine and glucuronic acid, previously shown5 to be an activator of certain kinin-forming agents, was much less active than the other sulphopolysaccharides examined. The amounts of bradykinin formed by optimal concentrations of cellulose sulphate in rat plasma were the same as those resulting from the exposure of plasma to powdered glass6. Either treatment led to a comparable depletion of plasma-kinin precursor, so that pre-incubation of plasma with glass in the absence of 8HQ, followed by incubation with cellulose sulphate and quinoline, did not result in kinin activity while, reciprocally, pre-incubation of plasma with cellulose sulphate in the absence of 8HQ, rendered it unresponsive to subsequent activation with glass in the presence of 8HQ.