Formation and binding of histamine by rat tissues in vitro.

Several rat tissues decarboxylate Cl4 L-histidine and bind the resulting histamine in stable form. The pyloric portion of the stomach is by far the most active. Pretreatment of the rats with cortisone appears to reduce the histamine-binding activity of most tissues while prior adrenalectomy increases it. The stomach is the exception; here the reverse is true. Using rat lung as a test tissue, it was found that prednisone, prednisolone and 9-afluorohydrocortisone appear to be more active than cortisone or hydrocortisone in inhibition of histame bininding. The mechanism of this reduction of histamine-binding activity of rat lung involves the loss of extractable histidine decarboxylase activity. T HIS laboratory has shown that the formation and binding of new histamine in rat abdominal skin, both in vivo (I) and in vitro (2) is controlled by the adrenal cortex. When rats are pretreated with cortisone the rate of binding of new histamine is strongly inhibited. In adrenalectomized rats the rate is increased. We have now extended this investigation to other rat tissues, investigated cortisone analogs for cortisone-like activity on histamine formation, and obtained evidence on the mechanism of this phenomenon. MATERIALS AND METHODS Cl4 L-histidine labeled in the a-position of the imidazole ring was synthesized in the usual manner (3). The specific activity of this batch was 2.4 X 10~ cpm/ mg base measured with a flow counter. The procedure for incubation of tissue minces with Cl4 L-histidine and subsequent extraction and determination of Cl4 histamine by isotope dilution has been published (2). EXPERIMENTAL AND RESULTS Histamine Binding by Rat Tissues. Various rat tissues were examined for ability to decarboxylate Cl4 L-histidine and to bind the Received for publication October 31, 1955. 1 This investigation was supported by a research grant, A-1087, from the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health. resulting C l4 histamine in stable condition.2 The relative histamine-binding capacity of these tissues is shown by the data of table I. Effect of Cortisone and Adrenalectomy on Histamine Binding by Various Rat Tissues. Cortisone acetate (Cortone, Merck) 5 mg was administered intramuscularly for 3 successive days. The rats were killed and the tissues examined about 2 hours after the last injection. Adrenalectomy was performed 3 days before testing the tissues. Effects on the histamine-binding power of the tissue are shown in table 2. Inhibition of Histamine Formation by Cortisone Analogs. Some cortisone analogs have greater anti-inflammatory activity than cortisone itself; their effect on histamine binding in rat lung was studied. Each steroid3 was ground in Merck’s Aqueous Vehicle No. I to give a find suspension. Rats were injectedintramuscularly for 3 successive days. They were killed about 2 hours after the final injection and the lung examined for histamine-binding activity. Results are shown in table 3. 2 Our interest is in the formation of histamine in tissues which possess a histamine-binding mechanism. The procedure used in the present investigation measures only Cl4 histamine which is newly formed and ‘bound’ so that it is not removed from the tissue during incubation or washing. 63 by 10.0.33.2 on M ay 2, 2017 http://ajple.physiology.org/ D ow nladed fom 64 RICHARD W. SCHAYER TABLE I. RELATIVE HISTAMINE-BINDING CAPACITIES OF DISCUSSION VARIOUS RAT TISSUES Several rat tissues decarboxylate small