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Year : 1985  |  Volume : 17  |  Issue : 1  |  Page : 55-59

Alpha-adrenocepter hyper-responsiveness in asthma: analysis of dose-response curves for cutaneous vasoconstrictor action of adrenaline in normal and asthmatic subjects

Correspondence Address:
S S Mahajani

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1. The dose-response curves of adrenaline for its cutaneous vasoconstrictor action, were analysed in 21 normal and 24 asthmatic subjects. 2. The vasoconstrictor responses to adrenaline were studied by determining the to 5 of disappearance of interacutaneously injected radioactive iodine (Na131) in absence and presence of doses of adrenaline (8-256 pg) and were expressed in terms of percent reduction in basal blood flow. 3. The skin blood flow in normal subjects was 15.82 ( 0.60 ml/min/100g of tissue. It was noted that there were two distinctly heterogenous groups in asthmatic subjects, with respect to skin blood flow, one with values similar to normal and the other with significantly higher blood flow (23.94 ( 1.39). The subjects in the latter group showed marked tendency of wealing at the injection sites. 4. The vasoconstrictor responses to the threshold doses of adrenaline (8+ 16 pg) were not significantly different in asthmatics having higher skin blood flow, as compared with that in the normal subjects. However, in asthmatics whose skin blood flow was similar to that of normal subjects this threshold response was significantly enhanced. 5. The dose-response curve in asthmatic subjects, exhibited a marked shift to the left, indicating an increased responsiveness of the alpha-adrenoceptors. The slope of the curve in asthmatic subjects was steeper and the maximal response attainable was higher. 6. It is possible that the basal hyperemia, observed in a group of asthmatics, presumably due to hyper-responsiveness to injection trauma (histamine hypersensitivity), counteracted the weak vasoconstrictor action of threshold dose of adrenaline. 7. The present observations confirm that the enhanced vasoconstrictor responses, seen in asthmatics indicate a true hyper responsiveness of the alpha- adrenoceptors and are not evident due to higher basal blood flow values.


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