Histamine Release Induced by Human Leukocyte Lysates REABSORPTION OF PREVIOUSLY RELEASED HISTAMINE AFTER EXPOSURE TO CYCLIC AMP-ACTIVE AGENTS

Abstract

The role of cyclic AMP in histamine release induced by human leukocyte lysates was investigated. Leukocytes were incubated with leukocyte lysates prepared by ultrasonic disruption, and histamine was determined fluorimetrically. Several cyclic AMP-active agents had a marked inhibitory effect on histamine release. Theophylline and isoproterenol produced 50% inhibition at concentrations of less than 10^-5 M. Prostaglandin E₁ and dibutyryl cyclic AMP inhibited release by 50% at 7 × 10^-8 M and 6 × 10^-5 M concentrations, respectively. Histamine, which has recently been shown to increase leukocyte cyclic AMP, had a pronounced inhibitory effect on lysate-induced histamine release, producing 50% inhibition at a concentration of only 2.5 × 10^-12 M. Leukocytes, incubated with leukocyte lysates, were sampled at various times and assayed for free histamine released into the incubation mixture supernates, and for bound histamine associated with the leukocyte buttons after centrifugation. Theophylline, prostaglandin E₁ and dibutyryl cyclic AMP not only blocked histamine release, but also caused a progressive decrease in free histamine when added at any time up to 30 min after initiation of the release reaction. As the free histamine decreased after addition of the inhibitors, there was a corresponding increase in the bound histamine, suggesting that previously released histamine was reabsorbed by the leukocytes after exposure to cyclic AMP-active agents. Continued incubation of leukocytes in their own histamine after completion of the release reaction also resulted in reabsorption of the previously released histamine. Previous studies have indicated that cyclic AMP inhibits leukocyte histamine release. The results of the present studies suggest that cyclic AMP modulates histamine release induced by human leukocyte lysates by stimulating reabsorption of histamine from the extracellular environment. These studies also suggest that previously released extracellular histamine may stimulate its own reabsorption by increasing the intracellular level of cyclic AMP.