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Flunarizine, a calcium entry blocker drug, concentration-dependently inhibited FMLP and A23187-induced aggregation, enzyme release and superoxide anion generation from human granulocytes. A23187-dependent granulocyte aggregation was also studied in media devoided of Ca++ or Mg++. Flunarizine (2.4 x 10(-5) M) significantly affected not only Ca++-supported but also Mg++-sustained granulocyte aggregation. The inhibiting effect of the drug was reversed by increasing extracellular level of Ca++ (1.2 mM) or Mg++ (2 mM). In this "in vitro" model, the role of flunarizine as a specific Mg++ entry blocker was suggested.

Diazepam (DZP) inhibited in vitro in a concentration-dependent manner superoxide anion generation and chemiluminescence from human neutrophils stimulated by the formylated oligopeptide FMLP and by the calcium ionophore A23187. The dose-dependent inhibitory effect of DZP on A23187-dependent superoxide generation in the presence of Ca++ 0.6 mM was highly antagonized by increasing extracellular Ca++ concentration to 1.5 mM and to 2.0 mM. Ro 5-4864, a specific ligand for peripheral type benzodiazepine (BZ) binding site, inhibited superoxide generation induced by FMLP, while clonazepam (CNZ), which is selective for brain sites, did not possess any activity. Ro 15-1788, a central type BZ receptor antagonist, did not show any antagonistic activity on DZP-dependent inhibition. A new physiological property for substances presenting an affinity for peripheral type BZ binding sites is supposed. The inhibitory effect of BZ on neutrophil functions seemed to be associated with a Ca++-involving mechanism.

Drugs such as dipyridamole (200 micrograms/kg/min), an adenosine uptake inhibitor, and theophylline (300 micrograms/kg/min), an adenosine receptor antagonist, respectively increased and decreased postischemic hyperemia in normal subjects, as well as in POAD patients. Moreover, dipyridamole pretreatment was able to antagonize the reduction of peak flow induced by nifedipine, and the potentiating effect of flunarizine on postischemic hyperemia was affected significantly by theophylline, thus suggesting a possible interference of calcium entry blocker drugs with the endogenous adenosine system. In a cellular model (polymorphonuclear leukocytes--PMN) the inhibitory effect of calcium entry blockers on stimulated functions (degranulation and free radical production) was highly antagonized by theophylline. Finally, a 1H-NMR spectroscopy study showed a binding interaction between adenosine and flunarizine on the cell membrane. An adenosine-receptor coupling to the calcium entry blocker channels is suggested.

The effects in vitro of heparin on different functions of human neutrophilic leucocytes were assessed. Granulocyte aggregation, enzyme release and superoxide anion generation induced by FMLP (10(-6) M), ConA (30 micrograms/ml), and A 23187 (5 microM) were evaluated. Heparin was able to inhibit, in a dose-dependent way, FMLP-mediated and ConA-mediated granulocyte activation. Heparin inhibited cellular aggregation at the final concentration of 100-500 micrograms/ml, while the inhibiting effect on enzyme release and superoxide anion production was present at lower concentrations (10-100 micrograms/ml). No activity was observed on A 23187-induced granulocyte stimulation. The inhibiting effect of heparin on FMLP-induced granulocyte activation proved to be time-dependent. The hypothesis that an interaction of heparin with cells may possibly initiate the inhibitory effect is proposed.

Captopril, competitive inhibitor of angiotensin converting enzyme, is clinically employed for its antihypertensive activity and drug-dependent granulocytopenia or agranulocytosis have been seldom observed during treatment. In previous unpublished studies an activating effect of the drug on the complement alternate pathway has been demonstrated. In this paper we demonstrate that captopril-treated serum is able to "in vitro" induce granulocyte activation and aggregation. Granulocyte aggregation was shown by the turbidimetric method and cellular activation was confirmed by the release of the granule associated enzyme lysozyme and beta-glucuronidase. On this basis complement-mediated leukoaggregation and leukosequestration in vivo could be proposed as the effector mechanism of peripheral leukopenia.

Flunarizine inhibited FMLP- and A23187-induced aggregation, enzyme release and O2- generation from human PMN as a function of its concentration. A23187-dependent PMN aggregation was also studied in media devoid of Ca++ or Mg++. Flunarizine (2.4 X 10(-5)M) significantly affected not only Ca++-supported but also Mg++-sustained PMN aggregation. The inhibiting effect of the drug was reversed by increasing the level of Ca++ (1.2 mM) or Mg++ (2 mM). Nifedipine, another Ca++-entry blocker, was shown to inhibit enzyme release and O2- generation induced by FMLP and A23187 as a function of its concentration, but only slightly affected PMN aggregation at very high concentration (10(-4)M). A role for flunarizine as a specific Mg++-entry blocker is suggested.