Effects of two antihistamines on chloroquine and histamine induced weal and flare in healthy African volunteers.

This study investigated the effects of single doses of clemastine (2mg orally), mepyramine (2 micrograms intradermally) and placebo on weal and flare caused by intradermal chloroquine 2.5mg and histamine 2 micrograms in 11 healthy black subjects who experienced generalised pruritus with oral chloroquine. Compared with placebo, both antihistamines caused significant reductions in histamine-induced weal and flare. By contrast, chloroquine-induced weal and flare were not significantly altered by clemastine or mepyramine when compared with placebo. It is concluded that histamine is unlikely to be the main mediator of chloroquine-induced weal and flare. These findings are in consonance with the lack of significant effect of antihistamines on chloroquine-induced generalised pruritus.

Antimalarial activity of cyclosporins A, C and D.

Cyclosporin A (CsA) is an immunosuppressive drug widely used in organ transplants. It is also accumulated by the erythrocyte, a site that accommodates one of the stages of malaria parasite. We observe that CsA and its less potent immunosuppressive analogues CsC and CsD were as effective as chloroquine in inhibiting P. berghei malaria parasite development in vivo (when administered orally) and P. falciparum parasite in vitro. They were, however, not inhibitory to the liver stages and the gametocytes. In vivo the minimum effective dose was 10 mg/Kg administered on two consecutive days whereas, in vitro CsA and its analogues inhibited parasite development at concentrations of 10 micrograms/ml and above.

Anti-inflammatory, antipyretic and anti-malarial activities of a West African medicinal plant--Picralima nitida.

A preliminary pharmacological screening of the methanolic extract of Picralima nitida fruit was carried out. The extract showed potent and dose-dependent anti-inflammatory, antipyretic and anti-malarial activities. Given intraperitoneally, it inhibited carrageenan-induced rat paw oedema with IC50 of 102mg/kg, and with the highest dose tested (300mg/kg) producing 72.2% inhibition. On the LPS-induced pyrexia in rabbits, 50mg/kg of the extract produced a mean percentage antipyrexia of (38.7%) compared with (29.0%) by 200mg/kg of aspirin. In a 4-day in vivo schizontocidal test in mice infected with P. berghei berghei, up to 300mg/kg daily for 4 days was ineffective in preventing the development of parasitaemia or the consequent mortality. However, marked inhibitory activity was obtained on multi-drug resistant human P. falciparium parasites cultured in in vitro. The dose causing 50% inhibition of parasite growth was 1.75 micrograms/ml compared with (0.14 microgram/ml for chloroquine. The results confirm the medicinal value of this plant and thus justify its use by natives of W. Africa.

The role of neutrophils in acute and chronic inflammation in rats.

The effect of neutropenia on acute and chronic inflammatory oedema in rats was assessed using histamine, carrageenan and Freund's complete adjuvant as inducers. Neutropenia (about 85% reduction in peripheral blood neutrophil count) was induced with intraperitoneal administration of 2.5 mg/kg methotrexate for three consecutive days. Acute paw oedemas induced with carrageenan and Freund's complete adjuvant, but not that induced by histamine, were significantly decreased in neutropenic animals compared with controls. In adjuvant-induced chronic knee swelling (Adjuvant arthritis), neutropenia produced small, statistically non-significant, suppressive effect. In contrast, it significantly suppressed adjuvant-induced chronic paw swelling, although suppression was observed only in the late phase component of the swelling. The results suggest that neutrophils are involved in certain acute and chronic inflammatory responses but not in others.

Halofantrine-induced pruritus amongst subjects who itch to chloroquine.

The incidence and nature of pruritus induced by chloroquine and halofantrine were studied in 82 patients with acute malaria and in 40 healthy subjects, using a visual analogue scale for quantitating pruritus. Results showed that the proportion of patients with acute malaria manifesting itch to halofantrine was significantly lower than the proportion manifesting itch to chloroquine. Furthermore, the intensity and duration of halofantrine-induced pruritus were significantly lower than those of chloroquine-induced pruritus. The few patients who itched to halofantrine all had a history of itching to chloroquine. The incidence and intensity of chloroquine-induced pruritus were significantly higher in patients with malaria than in healthy subjects. By contrast, there was no significant difference between malaria patients and healthy subjects as regards halofantrine-induced pruritus. These results suggest that itchers to halofantrine may constitute a small group within the population of itchers to chloroquine. Malaria infection appears to enhance chloroquine-induced pruritus but not halofantrine-induced pruritus and this may be of therapeutic importance.

Inhibition of histamine release from human lung and rat peritoneal mast cells by cyclosporin-A.

Cyclosporin A (CS-A) partly inhibited IgE-mediated histamine release from human lung tissue in vitro (chopped and collagenase-dispersed preparations). Inhibition started at concentrations within the clinical blood level of the drug, but the IC50 was much higher (10-50 microM; 50% inhibition reached only in some experiments). CS-A also inhibited histamine release from rat peritoneal mast cells (RPMC) induced by antigen, concanavalin-A (Con-A), compound 48/80 and ionophore A23187. The IC50 values were 0.3, 23.0, and 33.0 microM for Con-A, A23187 and ovalbumin respectively. Inhibition of 48/80-induced release did not reach 50%. By comparison with human basophils the human lung and RPMC were less sensitive to the inhibitory action of CS-A. The IgE-mediated Schultz-Dale reaction in human lung strips was slightly and inconsistently inhibited by CS-A, but IgG1-mediated reaction in guinea-pig lung strips was potentiated by the drug.

Suxamethonium-induced histamine release from the heart of naïve and suxamethonium-sensitized guinea-pigs: evidence suggesting spontaneous sensitization in naïve animals, and relevance to anaphylactoid reactions in man.

A guinea-pig model for anaphylactic and anaphylactoid reactions to suxamethonium was evaluated. 'Sensitization' to that drug was demonstrated both by cardiac anaphylaxis in the Langendorff preparation, and by serum antibody studies. Spontaneous sensitization to cross-reacting chemicals in a proportion of control animals is strongly suggested, somewhat akin to spontaneous sensitization in patients with anaphylactoid reactions to neuromuscular blockers on first exposure, and in whom IgE antibodies are detected.

Antigen-induced formation of a lymphokine with a possible role as a mediator of the late component of dual allergic reaction.

In a penicillin-allergic patient who showed a strong dual skin reaction (immediate and late components) to an intradermal injection of the antigen, we investigated the possibility that the lymphokine, histamine-releasing factor (HRF), which has been shown to release histamine from human basophils and mast cells, might play a part in the elicitation of the late phase of the 'dual reaction'. In vitro stimulation of this patient's lymphocytes, but not those of a patient with a monophasic (immediate) reaction with the antigen, caused the production of a large amount of HRF, while a moderate lymphoproliferation occurred in both patients. The purified HRF released histamine from the patient's own leucocytes and also caused immediate wheal and flare reaction on intradermal injection.

Histamine releasing factor is not an interferon.

The speculation that human histamine releasing factor (HRF) - a lymphokine that releases histamine from human tissues, might be the same as gamma-interferon was investigated. The speculation arose from the fact that HRF and gamma-interferons are both lymphokines and have both been reported to affect histamine release from human basophils. Using purified gamma-interferons either naturally obtained or E. coli-derived (recombinant DNA technique), as well as alpha-, alpha-2, arg, and beta-interferons, it was found that: Unlike HRF, the interferons neither induced histamine release nor affected antigen-induced histamine release from human basophils in vitro. HRF is partially acid-stable whereas gamma-interferon is acid labile. HRF samples had little interferon activity which did not correlate with HRF activity. The estimated molecular weight of HRF is 12,000-18,000 daltons and contrasts to those of interferons, which exceed 30,000 daltons. The results strongly suggest that HRF is very unlikely to be a gamma-interferon or indeed any other class of interferon.

Dextran-induced gastric acid secretion in rats.

Dextran C (M.W. 60,000-70,000) employed as plasma expander in the treatment of hypovolemic shock, and which is known to induce histamine release from rat mast cells was studied for its effect on gastric acid secretion in rats. Dextran at doses even lower than the therapeutic dose in man (8-250 mg/kg) induced significant gastric acid secretion in intact anaesthetized rats. Pretreatment of the animals with 1 mg/kg cimetidine significantly reduced the increase in acid secretion while a higher dose of 10 mg/kg completely abolished the effect. The result thus suggests that dextran-induced gastric acid secretion in rats is mediated through histamine release.

Cytoprotective effect of pirenzepine and palm wine on rats gastric mucosa.

Pirenzepine (Gastrozepin--Boechringer Ingelheim) is selective antimuscarinic blocker (MI-blocker) which has been used in the treatment of peptic ulcer because of its ability to reduce gastric acid secretion. But pirenzepine has also been found to have a cytoprotective effect on gastric mucosa in rats. The aim of the present investigation was to find out if palm wine also has any cytoprotective effect on rat gastric mucosa. Gastric mucosal ulcerations were induced with absolute ethanol. It was found that Pirenzepine induced 57% cytoprotection while palm wine induced 24% cytoprotection in rat gastric mucosa. The protection with the latter substance was not statistically significant, while the effect with pirenzepine was significant.

Gastrointestinal toxicity of melos conquer mixture in rats.

GIT effects of Melos Conquer Mixture were investigated - using albino wister rats. Conquer Mixture was administered orally at different concentrations whereas the control group received water. The experiment lasted from 3 to 21 days. Pathological examination was carried out on the dead animals. The animals showed (1) loss of weight and appetite (2) weakness (3) faeces was soft (4) out of 10 animals which received 1.20 ml/kg died on day 5(5) the Glt of the dead rats was virtually empty except in the colon, (6) pieces from various parts of GIT revealed evidence of acute and sub acute inflammatory cellular reactions. The results indicate that Conquer Mixture may be toxic to the gastrointestinal tract and suggest that a re-evaluation of the therapeutic usefulness of the drug in the management of malaria is warranted.

Histamine releasing lymphokine: preliminary evidence of membrane receptors on basophils.

Histamine release induced by the lymphokine-histamine releasing factor (HRF), like IgE-mediated release is a two step event--the Ca2+-independent activation step in which HRF primes the cells for histamine release and the Ca2+-dependent histamine release. The stimulus produced by the activation step decays relatively slowly and exponentially with a half-time of 38 min. By the 'receptor desensitization' approach, HRF appears to possess specific receptors on basophils as demonstrated by its ability to desensitize the cells to itself for subsequent histamine release. Cross desensitization experiments further suggested that a close relationship might exist between any such receptors and cell-bound IgE molecules, since desensitization of cells to anti-IgE also resulted in their desensitization to HRF as well; though the reverse was not the case. Nevertheless, any such relationship does not involve binding and cross linking of cell-bound IgE molecules by HRF. The putative HRF receptors may be distinct from those proposed for macrophage migration inhibitory factor (MIF) and leucocyte migration inhibitory factor (LIF) since, unlike the latter lymphokines whose interactions with their target cells show specificity for certain simple sugars, HRF's interaction with basophils show no such specificity to any of the simple sugars tested.

Histamine-releasing lymphokine--characteristics of its production.

The in vitro production of the histamine-releasing lymphokine (histamine-releasing factor, HRF) was studied. HRF was found to be producible from the mononuclear cells of most individuals following stimulation with the T-cell mitogen-concanavalin-A (Con-A). Kinetic studies showed that HRF production was an early event in cellular response to activation--beginning as early as 6 h after activation thus preceding lymphoproliferation which was not apparent until about 24 h after activation. Only a 3 h pulse-stimulation of the cells was found to be necessary for HRF production to occur. Furthermore, the presence of foetal calf serum supplement in the culture medium was found to be unimportant for production. Inhibitors of DNA, RNA and protein synthesis--mitomycin C, actinomycin D and puromycin respectively, in a dose range of 10-25 micrograms/ml, completely abolished HRF production. The results are discussed with regards to the nature of HRF as a genuine product of lymphocyte activation.

Cardiac anaphylaxis: Part II: The role of prostaglandins, thromboxanes and leukotrienes in C.A.

The possible mediator role of the products of the cyclo-oxygenase and lipoxygenase pathways (namely the endoperoxides, prostaglandins and thromboxane A2, and leukotrienes respectively), in cardiac anaphylaxis are discussed. A cyclo-oxygenase product would appear to be responsible for the early fall in coronary blood flow and leukotrienes C4 and D4 for the late fall in coronary blood flow and for the prolonged contractile failure observed in cardiac anaphylaxis. A model for the role of histamine and arachidonate metabolites in cardiac anaphylaxis is presented at the end of the summary and conclusions.

Release of slow reacting substance (SRS) from human leucocytes by lymphokine.

A human histamine releasing lymphokine (histamine releasing factor, HRF) was studied for its ability to release slow reacting substance (SRS) alongside histamine from human leucocytes. HRF was found to release a substantial amount of SRS from human leucocytes. The SRS was identified by its slow contraction of isolated guinea pig ileum preparation in the presence of atropine and mepyramine, inhibition of this action by the SRS antagonist FPL 55712, the inhibition of its production by eicosa--5, 8, 11, 14--tetraynoic acid (ETYA) but not indomethacin, and a final confirmation by a radioimmunoassay for leukotriene C4 (LTC4). Amounts of SRS ranging from a few nanograms to about 180 ng (eqt LTD4) could be released from 10(8) leucocytes depending on the dose of HRF, and there is a good correlation between the amount of SRS produced and the percentage histamine release accompanying it. These findings suggest that the human lymphokine (HRF) may play an important role in acute hypersensitivity and inflammatory reactions in addition to its traditional role as mediator of delayed hypersensitivity reactions.

Modulation of the effect of histamine-releasing lymphokine on human basophils.

Agents which increase or mimic intracellular cyclic 3',3'-adenosine monophosphate (cAMP) - theophylline dibutyryl cAMP (DBcAMP) and isoprenaline (in the presence of theophylline) - all produced pronounced inhibition of histamine release from human basophils, thus suggesting a regulatory role for the cAMP system. The effect of the flavonoids , quercetin and taxifolin , and the structurally-related cromone disodium cromoglycate (DSCG) was also studied. Only quercetin was effective in inhibiting histamine release. This is similar to the situation in IgE-mediated release. The microtubule stabilizer, deuterium oxide (D2O), at a concentration of 44% caused up to three-fold increase in release. This supports the belief that histamine release by this histamine-releasing factor ( HRF ) is a secretory process. Indomethacin and 5,8,11,14-eicosatetraynoic acid (ETYA), which are modulators of arachidonic acid metabolism, produced little or no inhibition of histamine release by HRF , thus suggesting that the release is largely independent of the arachidonate system, probably unlike IgE-mediated release.

Effects of leukotrienes C4 and D4 on guinea-pig heart and the participation of SRS-A in the manifestations of guinea-pig cardiac anaphylaxis.

Synthetic leukotrienes C4 and D4 (LTC and LTD) were found to possess potent coronary vasoconstrictor and cardiac depressant actions on isolated guinea-pig hearts. We therefore went further to investigate the possibility that endogenously released slow-reacting substance of anaphylaxis (SRS-A) might be responsible for the coronary vasoconstriction and negative inotropism in guinea-pig cardiac anaphylaxis. Results using time-course analysis as well as the specific SRS antagonist FPL 55712 have shown that SRS-A released during cardiac anaphylaxis was unlikely to be responsible for the early and most dramatic phase of coronary vasoconstriction that usually occurred at the 2nd min after antigen challenge, but could possibly be responsible for the latter and more prolonged phase occurring between the 6th and 14th min. This is because SRS-A release was found to peak at the 4th min after antigen challenge, 2 min after vasoconstriction had already peaked. Moreover, this early component of coronary vasoconstriction could not be blocked by FPL 55712, whereas the latter component was significantly reduced by the antagonist. The negative inotropism following cardiac anaphylaxis was also found to be significantly reduced by FPL 55712, thus suggesting SRS-A involvement. However, our experiments did not show whether the two actions were direct effects of SRS-A or whether contractility failure was a consequence of coronary vasoconstriction.

A study of histamine release from human basophils and lung mast cells by products of lymphocyte stimulation.

It has been previously reported by Thueson and his co-workers [1] that lymphokine-containing supernatant of cultured human peripheral blood lymphocytes stimulated with Concanavalin-A (Con-A) is capable of releasing histamine from human basophils. Here we confirm such findings, show that such release is additive to that due to immunological stimuli (Anti-IgE and antigen) and describe its characteristics and effect in lung tissue. The lymphokine was found to induce a small histamine release from chopped or enzyme-dispersed human lung tissue. As was the case with basophils, the release from lung tissue by this factor, though small, was also found to be additive to that induced by anti-IgE when both agents were added simultaneously. Histamine release from leucocytes by neat supernatant ranged from 9 to 35% and up to 55% when concentrated four-fold. The release resembled that of IgE-mediated reactions in many respects including temperature and calcium dependence, time course and susceptibility to metabolic inhibitors - thus suggesting a non-cytotoxic mechanism. These results show that histamine release by this lymphokine(s) possesses most of the features of an active secretory process. They also suggest that the histamine-releasing factor (HRF) in lymphokine-containing supernatants might be involved in the modulation of type I allergy in humans, apart from its involvement in delayed-type hypersensitivity.