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Medical Research Society supports the theory that the high level of IgE in this community is due to parasitic infestations. However, cutaneous reactions to D. pteronyssinus were larger in the asthmatics than in the controls which indicates that asthmatics may also have increased levels of I& speci6c for this allergen. The low prevalence of asthma in New Guineans does not appear to be explained by a reduced atopic tendency and, though ethnic factors cannot be excluded, it is likely that this is mainly due to environmental factors. 2. THE INFLUENCE O F BRONCHOMOTOR TONE ON BRONCHIAL REACTIVITY MALCOLM K. BENSON Cardiovascular Research Institute, Uniuersity of California, San Francisco, California (Introduced by N.B. PRIDE) The parasympathetic nervous system has been shown to have an important influence on resting bronchomotor tone and to mediate reflex bronchoconstriction. Airway responses to various stimuli are frequently studied before and after vagal blockade and it is often implied that a reduction in response indicates a reflex mechanism. However, vagal blockade also reduces airway tone and thus alters baseline conditions. This in itself may alter the response to bronchoconstrictor stimuli. The effect of changes in bronchomotor tone on histamine induced bronchoconstriction was examined by measurement of changes in bronchial diameter in dogs in whom airways were outlined by tantalum dust. In each dog the airway response was taken as the change seen in twenty airways randomly selected and ranging in size from the main bronchi to airways 2 mm in internal diameter. Bilateral vagotomy was performed and reactivity to inhaled histamine measured (1) without vagal stimulation and (2) with electrical stimulation of the distal ends of the cut vagi. In seven dogs when vagal tone was induced in this way airway calibre was reduced as expected (mean reduction 0.9k0.36mm). Doses of histamine which had little effect on airway diameter when the vagi were unstimulated (mean reduction 0 3 k 0 1 4 mm) produced significantly greater changes during vagal stimulation (mean reduction 1-2f 044mm) (P.c 0~001, paired t test). In three dogs a wide range of histamine doses were studied and dose-response awes were constructed with and without vagal tone. Adding vagal tone decreased the threshold dose of histamine required to reduce airway diameter. This study demonstrates that variations in the level of resting bronchomotor tone will alter bronchial reactivity to bronchoconstrictor stimuli. The ‘reflex blockade’ produced by atropine could also be explained on this basis. 1 3 ~ 3. THE TIME COURSE OF CONTRACTION IN HEART MUSCLE PREPARATIONS EQUILIBRATED WITH STRONTIUM A. H. HENDERSON and M. R. CATTELL Department of Cardiology, Welsh National School of Medicine (Introduced by J. R. MUIR) Mechanical performance of cat and frog ventricular muscle preparations has been studied after equilibration with strontium in place of calcium in order to gain insight into underlying control mechanisms. The onset of mechanical activity is slowed in cat but not in frog heart muscle. This supports the view that activating cation is derived mainly from internal stores in mammalian but not in frog heart muscle, where the sarcoplasmic reticulum is poorly developed. The duration of contraction is prolonged in both species. In cat but not in frog heart muscle, a separate twitch and plateau phase of contraction can then be distinguished. The plateau phase is augmented in the first contraction after adding adrenaline whereas the twitch phase is increased more in subsequent contractions. The plateau can also be augmented by adrenaline added during the course of contraction. These observations support the view that influx of cations can contribute directly to mechanical activation. 4. SOME EFFECTS OF DISODIUM ETHANE-1- HYDROXY-1,I-DIPHOSPHONATE (EHDP) ON CALCIUM METABOLISM IN MAN R. J. WALTON,R. G. G. RUSSELL,R. SMITHand G. WARNER Nufield Departments of Orthopaedic Surgery and Medicine, University of Oxford EHDP is able to inhibit calcification and bone resorption in experimental animals and is currently under investigation in man as a treatment for Paget’s disease of bone and other conditions. At the commonly used dose of 20 mg/kg/day by mouth, EHDP consistently produces a marked rise in plasma inorganic phosphate. This is due to an alteration in the renal tubular handling of phosphate and does not appear to be caused by altered plasma levels of parathyroid hormone, growth hormone, thyroid hormones or cortisol. There is no comparable consistent change in the total plasma concentration or renal handling of calcium. EHDP has no significant effect on the 24-h urine excretion of calcium or on the intestinal absorption of calcium as measured by the whole body retention of oral 47Ca. It therefore seems unlikely that EHDP has any marked effect on the production of 1,25-