In Vitro Studies of the Mechanism of Anaphylaxis

Airway hyperresponsiveness to adenosine 5'-monophosphate in feline chronic inflammatory lower airway disease

Airway hyperresponsiveness is a key feature of human asthma and chronic bronchitis and response to the indirectly acting agonist adenosine 5'-monophosphate (AMP) is thought to reflect underlying airway inflammation. To examine whether airway responsiveness testing (ART) with AMP may be used to differentiate healthy cats from those with asthma (FA) and chronic bronchitis (CB), 24 cats (9 FA, 6 CB, 9 controls) underwent ART with AMP at concentrations of 0.1, 1, 10, 100 and 500mg/mL using barometric whole body plethysmography. The defined endpoint of ART, an increase in enhanced pause (Penh) exceeding 300% of the post-saline value (baseline), was reached in 9/15 patients (7 FA, 2 CB), but in none of the controls. Mean Penh (±SD) at baseline (BL) was 0.49±0.16 for cases, and 0.54±0.16 for controls, and was significantly increased after AMP challenge in clinical cases (2.62±2.20), but not in controls (0.63±0.30, P<0.05). After separating responder (R) and non-responder (NR) cases, a more pronounced difference after challenge was found (R: 3.96±1.84, NR: 0.6±0.21, P<0.001). The provocative concentration of the agonist that increased Penh to 300% of BL (PC Penh 300) in R cases was 52.98±48.04mg/mL AMP. Age had no influence on the responder status or PC Penh 300. It was concluded that AMP challenge may offer a new method for the identification of cats with lower inflammatory airway disease, and possibly for monitoring disease progression or response to therapy.

Histamine release and calcium concentrations in rat mast cells are dependent on intracellular ATP: effects of prostaglandin D2

When PGD2 (10 microM), was added to rat mast cells, it caused a rapid increase in adenosine 3',5'-cyclic monophosphate (cyclic AMP) and decrease in adenosine 5'-triphosphate (ATP), both of which recovered to their original levels within 2 min. The accumulation of cyclic AMP was maximal at 30 s after challenge with PGD2. The minimum level of ATP was observed at 30 s after addition of PGD2. The initial rise in [Ca2+]i and the histamine release induced by anti-IgE (200 micrograms/ml) were strongly inhibited at 30 s after incubation of the mast cells with PGD2. Removal of glucose from Tyrode-Hepes solution caused a rapid decrease on ATP level in mast cells, and showed strong inhibition on the rise in [Ca2+]i and histamine release induced by anti-IgE. Addition of glucose to the mast cells induced a time-dependent increase in ATP, and the rises in [Ca2+]i and histamine release were closely correlated with the recovery of ATP. These results suggested that the inhibitory mechanism of PGD2 on the initial rise in [Ca2+]i and histamine release induced by anti-IgE was due to the inhibition of ATP-dependent CA(2+)-release from the intracellular Ca(2+)-stores.

Clinical aspects of the melatonin action: impact of development, aging, and puberty, involvement of melatonin in psychiatric disease and importance of neuroimmunoendocrine interactions

During the last decade we have learned much on physiological changes in the secretion of the pineal hormone melatonin (MLT) in man. Reportedly, there is little or no MLT secreted before age 3 months. Then MLT production commences, becomes circadian, and reaches highest nocturnal levels at the age of 1-3 years. During all of childhood nocturnal peak levels drop progressively by 80% until adult levels are reached. This alteration appears to be the consequence of increasing body size in face of constant MLT production during childhood. The biological significance of this MLT alteration is presently unknown. Because of conceptual considerations, major depressive syndrome (MDS) and seasonal affective disorder (SAD) have been in the focus of pineal research for several years. Although in these disorders alterations in MLT levels could not be substantiated, light therapy, a consequence of this research, was discovered as an effective treatment for SAD and perhaps for MDS. In addition, there is some recent evidence for low MLT levels in schizophrenia. Finally, the potential effect of MLT in neuroimmunoendocrine interactions is presently explored. Reportedly, in vitro studies and animal experiments give evidence for a modulatory role of MLT in the immune response. However, the exact way of this possible action of MLT remains to be clarified. Clinical studies are too scant for a meaningful estimation of MLT's involvement in human neuroimmunoendocrine interactions.

Mechanism of action of MY-1250, an active metabolite of Repirinast, in inhibiting histamine release from rat mast cells

1. When MY-1250 (3.6 x 10(-5) M) was added to mast cells, it caused a rapid increase in adenosine 3':5'-cyclic monophosphate (cyclic AMP) and decrease in adenosine 5'-triphosphate (ATP), both of which recovered to their original levels within 2 min. The accumulation of cyclic AMP was maximal at 20 s after challenge with MY-1250. The minimum level of ATP was observed at 20 s after addition of MY-1250. 2. The initial rise in [Ca2+]i and the histamine release induced by DNP-AS antigen (40 micrograms ml-1) was most strongly inhibited at 20 s after incubation of the mast cells with MY-1250. 3. MY-1250 strongly and dose-dependently inhibited the histamine release from rat mast cells induced by antigen. Moreover, MY-125 strongly inhibited calcium ion mobilization from the intracellular Ca(2+)-store. 4. These results suggested that the inhibitory mechanism of MY-1250 on the initial rise in [Ca2+]i and histamine release induced by antigen was due to the inhibition of ATP-dependent Ca(2+)-release from the intracellular Ca(2+)-stores.

Newer antihistaminic agents

Two new antihistamines with properties different from those of currently available drugs are nearing licensure. Named terfenidine and astemizole, they are almost exclusively H1-antagonists, lacking anticholinergic and sympathetic activity. They fail to penetrate the central nervous system and lack sedative effects. They are long-acting and require less frequent doses. Thus they allow sustained antihistaminic action without the usual side effects.

The rate of equilibration in a competitive n drug system and the auto-inhibitory equations of enzyme kinetics: some properties of simple models for passive sensitization

The solution of the equation for the rate of equilibration of n drugs all competing for the same receptors is presented and the two-drug case is given explicitly. The case of two com­peting drugs with the same rate constants is discussed in detail as it is the simplest plausible model for the rate of passive sensitization. The predictions of this model are compared with present knowledge about the rate of onset and the persistence of sensitization. The model suggests that if the observed rate of sensitization depends on the rates of reaction with receptors then (1) equilibration will be too slow to be seen in the usual length of passive sensitization experiment in vitro , (2) there will be no fast initial phase of sensitization, and (3) sensitizing immunoglobulins which persist for a long time (e. g. those of man and rat) will have a slower rate of onset than those which persist for a shorter time (e. g. those of the guinea-pig). It is also emphasized that there are at present no firm grounds for supposing that the more persistent sensitizing antibodies have a higher affinity for cells than the less persistent since the association rate constants are unknown. The model proposed by Mongar & Winne, which accounted for the auto-inhibition observed during passive sensitization by a mechanism involving two-point attachment of antibody to cells, is discussed in relation to uncompetitive and non-competitive models for auto­-inhibition. These models all fit the available observations equally well but the last of them does not involve two-point attachment of antibody. The presence of non-specific immuno­globulin in the antibody preparation used is shown to have a potentially very serious effect on some of the parameter estimates in all three models, and corrections for errors from this source are discussed.