Bronchodilating effect of KC-404, a novel anti-asthmatic agent, and its derivatives in monkey

The inhibitory effect of 3-isobutyryl-2-isopropylpyrazolo[1,5-alpha]pyridine (KC-404) on aerosolized methacholine- and histamine-induced increase in total respiratory resistance (Rrs) was determined in monkeys using the forced 3 Hz oscillation method and was compared with the effect of aminophylline. The effects of several derivatives of KC-404 on methacholine-induced bronchoconstriction were also determined. All of the i.v. administered pyrazolopyridine derivatives showed an inhibition of the increase in Rrs induced by aerosolized methacholine. Among these derivatives, KC-404 exerted the most potent bronchodilating effect. KC-404 also inhibited the histamine-induced increase in Rrs. These effects of KC-404 were more potent than those of aminophylline. On the other hand, the dose of KC-404 tested caused an increase in heart rate, although the degree was moderate as compared with aminophylline. From the results obtained in this study, it is considered that the pyrazolopyridine derivatives, particularly KC-404, may be promising bronchodilators for the treatment of bronchial asthma.

Inhalation provocation test with house dust allergen using tidal breathing

Using the modified 3-Hz oscillation method, the inhalation challenge test was performed with house dust allergen upon subjects while tidal breathing throughout the test. Their total respiratory resistance (Rrs) was continuously monitored with the inhalation of saline as a control, and 250-, 50-, and 10-fold diluted allergen solution to the inhalation of aerosolized metaproterenol. The starting point of the induced bronchoconstriction was checked and as soon as Rrs increased up to twice the base-line value, the subjects inhaled the aerosolized metaproterenol. From the dose-response curve of Rrs, the dose of inhaled allergen (minimum dose) as bronchial sensitivity was determined; also the decreasing rate of respiratory conductance, which was calculated from the slope of elevation of Rrs, as bronchial reactivity. It was found that the more diluted allergen required for a positive skin reaction, the more likely the patients were to have a subsequent positive bronchial inhalation challenge to house dust allergen. There was a relationship between the increased bronchial reactivity and the increased RAST score. These results indicate that this inhalation challenge test is specific, safe, and time-saving.

Measurement of SRS-A activities in plasma of asthmatic patients

Ethanol extracts of arterial blood from 20 of 29 asthmatic patients during attacks produced sustained contractions of the guinea pig ileum. These contractions were inhibited by FPL 55712, a specific antagonist of slow reacting substance of anaphylaxis (SRS-A). SRS-A activity was significantly higher during attack than during remission. Reverse-phase high pressure liquid chromatography (HPLC) was performed on two extracts which had shown high SRS-A activity with bioassay. One extract showed double peaks, which had retention times identical to those of leukotriene (LT) C4 and LTD4. The other extract showed a single peak, which had a retention time identical to that of synthetic LTC4.