AIRWAY RESPONSIVENESS IN WHEEZY INFANTS - EVIDENCE FOR FUNCTIONAL BETA-ADRENERGIC RECEPTORS

The effect of nebulised salbutamol on the bronchial response to nebulised histamine was studied in five wheezy infants aged 3-12 months. The response to doubling concentrations of up to 8 g/l of histamine was assessed by the change in maximum flow at FRC (.ovrhdot.VmaxFRC), measured by flow-volume curves produced during forced expiration with a pressure jacket. The concentration of histamine required to provoke a 30% fall in .ovrhdot.VmaxFRC (PC30) was measured. All of the infants responded to low concentrations of histamine during control tests before and after nebulised saline (mean PC30 1.07 and 0.51 g/l). On a separate day there was a similar response to histamine before salbutamol (PC30 0.57 g/l), but after salbutamol the response was completely abolished up to the maximum concentration of histamine in all subjects (PC30 > 8 g/l). Thus wheezy infants have highly effective .beta.2 adrenoceptors in intrathoracic airways.