Repeated injections of rats with compound 48/80, a histamine liberator, results in a marked increase in histidine decarboxylase activity of the skin. The increase is roughly proportional to the duration of treatment. This eliminates activation of pre-existing histidine decarboxylase as a probable mechanism. The increase can be demonstrated in intact rats; therefore, rat skin histidine decarboxylase is an adaptive enzyme. It seems probable that 48/80 treatment leads to the production of new, resistant mast cells which are particularly active in forming histamine. This speculation is compatible with reports from other laboratories of histological studies on rats given 48/80. Implications of this finding are discussed.

Summary1. Cellulose sulphate, a kinin-releasing agent, produced fibrinolytic activity in plasma when administered intravenously to the rat but not when added to fresh rat plasma in vitro. The in viva effect was maximal within 1 min and disappeared within 10-20 minutes. It was retained in plasma taken 1 min after the injection and kept at room temperature for 30 minutes. 2. A decrease of anti-fibrinolytic potency measured against urokinaseactivated bovine plasmin, was shown to occur in plasma of rats given cellulose sulphate. 3. Activated rat plasma lysed heat-denatured fibrin: it probably contains free plasmin as well as plasminogen activator. 4. Adrenalectomized rats did not exhibit fibrinolytic activity nor statistically significant benzoyl-arginine ethyl ester-esterase activation in plasma after cellulose sulphate treatment. 5. Adrenalectomized rats had significantly increased levels of plasma kininogen, but were normally sensitive to the kininogen-depleting action of cellulose sulphate. 6. The increased plasma kininogen of adrenalectomized rats seems to be a consequence of the impairment of the plasminogen activating mechanism.

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