AIRWAY RESPONSES TO LOW CONCENTRATIONS OF ADRENALINE AND NORADRENALINE IN NORMAL SUBJECTS

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1 Quarterly Journal of Experimental Physiology (1985) 70, Printed in Great Britain AIRWAY RESPONSES TO LOW CONCENTRATIONS OF ADRENALINE AND NORADRENALINE IN NORMAL SUBJECTS K. E. BERKIN, G. C. INGLIS*, S. G. BALL* AND N. C. THOMSON Department of Respiratory Medicine and *M.R.C. Blood Pressure Unit, Western Infirmary, Glasgow (RECEIVED FOR PUBLICATION 27 SEPTEMBER 1984) SUMMARY Airway, cardiovascular and metabolic responses were measured in six normal subjects during separate infusions of adrenaline and noradrenaline. Four incremental infusion rates of the catecholamines (4, 10, 25 and 62-5 ng. kg-'. min -1) produced circulating levels of adrenaline and noradrenaline within the physiological range. Maximal expiratory flow rates at 25% of vital capacity measured from partial flow-volume curves increased sequentially with increasing adrenaline concentration. Increases in maximal expiratory flow rates at 25% and 50% of vital capacity measured from complete flow-volume curves were not statistically significant, nor were the changes in specific conductance. Small but insignificant changes were observed in heart rate and blood pressure during adrenaline infusion. Plasma glucose increased and serum potassium fell during adrenaline infusion. No significant airway, cardiovascular or metabolic responses were seen during noradrenaline infusion. These results suggest that adrenaline, at concentrations found in physiological circumstances, influences flow rates in small airways. Circulating noradrenaline does not appear to be important in the control of airway calibre in normal subjects. INTRODUCTION Bronchial smooth muscle has adrenergic receptors, which in the absence of an important direct sympathetic nerve supply (Richardson, 1979; Davis, Kannan, Jones & Daniel, 1982; Partanen, Laitinen, Hervonen, Toivanen & Laitinen, 1982) are probably influenced by the concentration of circulating catecholamines (Richardson, 1979; Widdicombe, 1963; Daniel, Davies, Jones & Kannan, 1980). However, adrenergic receptors are also present at prejunctional sites on the parasympathetic nerve supply to the airways (Richardson, 1979; Widdicombe, 1963; Daniel et al. 1980) and these could respond, therefore, to both neuronally released noradrenaline and circulating catecholamines. The bronchodilator effect of pharmacological doses of adrenaline given parenterally is well known, whereas noradrenaline appears to have little effect, but the importance of the normally circulating concentrations of the catecholamines in determining airway calibre is not established. Administration of adrenaline, achieving concentrations similar to those reached after strenuous exercise, has been reported to cause bronchodilation as assessed by changes in specific conductance (Warren & Dalton, 1983), a measure of large-airway calibre (Pride, 1971). However, neither the threshold concentration at which circulating adrenaline alters airway calibre, nor the main site of its action within the airways, that is on the small (peripheral) or large (central) airways, is known. Although noradrenaline administration at a single high rate of infusion to normal subjects was reported to produce no significant changes in specific conductance (Stone, Sarkar & Keltz, 1973), the circulating noradrenaline concentrations achieved during the infusion were not measured. We have determined, therefore, the threshold circulating concentrations of plasma 8-2

2 204 K. E. BERKIN, G. C. INGLIS, S. G. BALL AND N. C. THOMSON adrenaline and noradrenaline required to produce changes in airway calibre, assessed by lung function tests thought to reflect both large- and small-airway calibre. The catecholamines were infused separately at four incremental rates to produce plasma levels over a wide physiological range. Airway responses during the catecholamine infusions were compared with responses seen during a reference saline infusion and after salbutamol inhalation. In addition, changes in heart rate and blood pressure, plasma glucose and serum potassium were measured to assess cardiovascular and metabolic aspects of adrenoceptor responsiveness. METHODS Six normal subjects gave informed consent for the study, which was approved by the Hospital Ethical Committee. The subjects, mean age 29 years (range years) were non-smokers, had no history of chest disease and were taking no medication. All had forced expiratory volume in 1 s and vital capacity values within the predicted normal range. Airway resistance and thoracic gas volume were measured simultaneously in a constant-volume body plethysmograph (Fenyves and Gut) using the methods of Du Bois, Botelho & Comroe (1956). The results were expressed as specific conductance (Gs,aw), which is the reciprocal of airways resistance per litre of thoracic gas volume. The mean of eight values recorded was taken as Gsaw. Partial and complete expiratory flow-volume curves were obtained using a heated pneumotachygraph with integration of flow, recorded on an X-Y recorder (Hewlett-Packard 7041A). After 30 s of normal tidal breathing, a forced maximal expiration from end-tidal inspiratory volume to residual volume was performed to obtain the partial expiratory flow-volume curve. The patient then inspired from residual volume to total lung capacity and performed a second forced maximal expiration to residual volume to obtain the complete expiratory flow-volume curve. Flow rates at 25% and 50% of vital capacity were measured from the partial (V25 p) and complete ( V50,,) flow-volume curves. Eight curves were recorded for initial (base-line) readings and three curves were recorded for subsequent readings. Body plethysmographic measurements always preceded flow-volume recordings. Subjects attended the laboratory at 9.00 a.m. on two separate days, having had a light breakfast without tea or coffee. Adrenaline was infused on one day and noradrenaline on the other, single blind, on a random basis. Intravenous cannulae for infusing and sampling were inserted in the left and right forearms, respectively. After a 30 min rest, the subject remained seated in the body plethysmograph for the duration of the study period. A 30 min reference infusion of sodium chloride solution, 154 mmol. 1-1 (saline), by an electronic infusion pump (Treonic 1P3 Digital Syringe Pump, Vickers Medical) was followed by the catecholamine infusion given at four incremental rates of 4, 10, 25 and 62 5 ng. kg-. min-', each infusion period lasting 20 min to allow circulating catecholamine concentrations to become constant. This was followed by a second reference saline infusion lasting 20 min, after which 200,ug salbutamol was inhaled from a metered dose inhaler. The subjects were not aware of the nature or order of the infusions. Lung function tests (Gsaw, V25 p, and 50,c) were recorded 4 min before the end of each infusion period, and 15 min after salbutamol inhalation. Blood samples were taken immediately after the lung function recordings, but before the end of each infusion period, for measurement of plasma adrenaline, noradrenaline and glucose, and serum potassium. The blood for the catecholamine measurements was transferred immediately to cooled lithium heparin tubes, separated at 4 'C and stored at -70 'C until assayed within two weeks by a radioenzymatic method (interassay coefficient of variation 12%0) (Ball, Tree, Morton, Inglis & Fraser, 1981). Heart rate was monitored continuously and blood pressure was measured using a mercury sphygmomanometer at 10 min intervals throughout the experiment. Results are expressed as mean + S.E.M. Airway and metabolic responses during each infusion period and after salbutamol inhalation were compared with those seen during the first reference saline infusion. Paired t tests, with Dunnett's (1964) modification for multiple comparisons, were used to assess significance.

3 AIRWAY RESPONSES TO CATECHOLAMINES 205 3,-''--- -i--- \ 10 B ec 8 -,, \ +-I~~~~~~~~~~~I C.) 4 4 ~ ~ ~ ~ Cl C2 Infused catecholamine (ng kg-' min-') Fig. 1. Plasma adrenaline (0) and noradrenaline (0) concentrations (mean + S.E.M.) during the adrenaline study (A) and the noradrenaline study (B). Each set of catecholamine infusions (incremental infusion rates shown on horizontal axis) was preceded and followed by reference saline infusions (C, and C2). RESULTS Infusion of adrenaline at four different rates increased circulating adrenaline levels sequentially from nmol.1-1 (mean + S.E.M.) to nmol.1-1 (Fig. 1 A), statistically significant increases occurring during the two highest infusion rates of 25 and 62 5 ng. kg-'. min-' (P < 0-05). Adrenaline concentration fell to nmol.1-1 during the second saline infusion (C2). Noradrenaline concentration remained constant during adrenaline infusion. Noradrenaline infusion (Fig. 1 B) increased circulating noradrenaline levels sequentially from to nmol. 1-1, the increases during the two highest infusion rates reaching statistical significance (P < 0 05). Noradrenaline concentration fell to nmol. 1-1 during the second saline infusion (C2) and adrenaline concentration remained constant. The results for V25,P, V25,e) V50,. and Gsaw are shown in Fig. 2. V25,P rose sequentially during adrenaline infusion from to s'i, the increases during the two highest infusion rates of 25 and 62 5 ng. kg-1. min-' reaching statistical significance (P <0-05). V25,p fell to s-1 during the second saline infusion and a statistically significant increase to s-l was seen after salbutamol inhalation (P < 0 05). V e and V50,e both showed a similar tendency to increase sequentially with increasing adrenaline infusion rates and fall during the second saline infusion, but these changes were not statistically significant. During noradrenaline infusion, no statistically significant changes were seen in V p e or Although mean Gs aw did not change significantly during infusion ofeither catecholamine, three of the six subjects showed an increase in Gsaw during the adrenaline infusion. Salbutamol inhalation at the end of the infusion resulted in statistically significant increases (P < 0-05) in Gsaw, V50,e V25,, and V2,,p.

4 206 K. E. BERKIN, G. C. INGLIS, S. G. BALL AND N. C. THOMSON / C 42-1 * 3.4-3* Infused catecholamine (ng kg-1 min-) Fig, 2, f25,p9 V25,eq k5o, and Gsaw (mean + S.E.M.) during reference saline infusion (C, and C0) sequential adrenaline or noradrenaline infusions, and after salbutamol inhalation (S). 0. adrenaline study; 0, noradrenaline study. The two highest adrenaline infusion rates caused slight but statistically insignificant increases in pulse rate and systolic blood pressure and reduction in diastolic pressure (Fig. 3). The two highest noradrenaline infusion rates resulted in a slight increase in both systolic and diastolic blood pressure and a small reduction in pulse rate, but these changes were not statistically significant. Plasma glucose increased and serum potassium fell during the highest adrenaline infusion rate. These changes persisted during the second saline infusion (Fig. 3) and were statistically significant (P < 0-05). No significant changes were observed during noradrenaline infusion. DISCUSSION The plasma concentrations of adrenaline and noradrenaline achieved during the infusions were similar to those found in normal subjects under differing conditions (Cryer, 1980). With increasing adrenaline concentrations, V25,p, measured from the partial flow-volume curve, increased sequentially in all subjects. The bronchodilator effect ofadrenaline was emphasized by a reduction in flow rate observed when the adrenaline infusion was discontinued. Maximal expiratory flow rates taken from the complete flow-volume curves showed a similar, but statistically insignificant, tendency to increase during the adrenaline infusion. The measurements from the complete flow-volume curve are recorded after an inspiration

5 AIRWAY RESPONSES TO CATECHOLAMINES Systolic -+ Blood pressure 120 (mmhg) 901 Diastolic 70J 90 - Heart rate J (beats. min-') 70- Potassium 4.0 -ri X (mmol.1)1i * Plasma glucoseg1s (mmol I-,) 5] T Cl C2 S Infused catecholamine (ng kg min-') Fig. 3. Blood pressure, heart rate, serum potassium and plasma glucose concentrations (mean±s.e.m.) during reference saline infusion (C, and C2), and sequential adrenaline or noradrenaline infusions. 0O adrenaline study; 0, noradrenaline study. to total lung capacity and are less sensitive in detecting changes in airflow resistance than VP2,p (Bouhuys, Hunt, Kim & Zapletal, 1969). This is because an inspiration to total lung capacity may transiently reduce bronchomotor tone (Nadel & Tierney, 1961), thus partially obscuring changes in airway calibre. A statistically significant change in mean Gs aw was not observed during adrenaline infusion. In normal subjects, Gs aw is considered to reflect large-airway calibre (Pride, 1971), whereas VJ',p probably reflects more peripheral airway calibre (Bouhuys et al. 1969; Mead, Turner, Macklem & Little, 1967). Thus, our results suggest that adrenaline at concentrations similar to those found during exercise, has a broncilodilator effect predominantly on the peripheral rather than the central airways. Although increases in V2, p at the two lowest infusion rates were not statistically significant, an apparent dose-response relation was seen, suggesting that lower concentrations of adrenaline may affect small-airway calibre. A resting sympathetic drive to the central airways of normal subjects has been suggested by the changes seen in airway resistance after administration of,-adrenoceptor antagonists (Stone et al. 1973; Foley, Sigurdson, Conliffe, Fand & Anthonisen, 1982), but most workers (Richardson & Stirling, 1969; Tattersfield, Leaver & Pride, 1973, Bradley, Mills & Henderson, 1976) have found no change in lung function (including measurements thought to reflect small airway calibre; Tattersfield et al. 1973; Bradley et al. 1976) in these circumstances. A statistically significant but small increase in Gs aw during adrenaline infusion, achieving plasma concentrations similar to those observed in the present study, has been reported (Warren & Dalton, 1983). Three of our subjects showed small increases in Gs aw during the higher adrenaline infusion rates, not explained by differing plasma adrenaline concentrations, and all showed increases in Gsaw after a pharmacological dose of salbutamol. Intersubject

6 208 K. E. BERKIN, G. C. INGLIS, S. G. BALL AND N. C. THOMSON variation in response to physiological concentrations of fj-adrenergic agonists may, therefore, explain the apparently differing conclusions of the two studies. The preferential effect of adrenaline on the small airways could be explained by increasing numbers and/or responsiveness of /-adrenoceptors in these airways. Barnes, Basbaum & Nadel (1983), using autoradiographic methods, reported that 8-adrenoceptors were more numerous in the smaller bronchioles than in the central airways of ferrets. Whether a similar distribution of receptors is present in normal human airways is unknown. The peripheral effect of adrenaline could also be explained by the arterial blood supply to the lungs. A venous infusion may result in higher concentrations of adrenaline in the pulmonary artery, which supplies the small airways, than in the bronchial artery predominantly supplying the large airways, because of extraction of catecholamines by lung tissue. The absence of change in airway calibre during noradrenaline infusion suggests that a- and /31-adrenoceptors are not important in the control of airway calibre in normal subjects. This confirms and extends the results of Stone et al. (1973) and others (Cabezas, Graf & Nadel, 1971). Slight changes in heart rate and blood pressure were seen during the two highest catecholamine infusion rates but these were not statistically significant. The minimal cardiovascular response suggests that these concentrations of circulating catecholamines are not of major importance in the short-term regulation of heart rate and blood pressure (Warren & Dalton, 1983; Clutter, Bier, Shah & Cryer, 1980). A fall in serum potassium and an increase in plasma glucose were seen in response to the highest adrenaline infusion rate and these changes persisted during the second control infusion period. The increase in plasma glucose was similar to the increases described elsewhere (Warren & Dalton, 1983; Clutter et al. 1980). Reduction in serum potassium has been reported with pharmacological doses of salbutamol (Leitch, Glancy, Costella & Flenley, 1976) and adrenaline (Grassi, DeLew, Cingolani & Blesa, 1971), but the response to graded infusions of adrenaline using very low doses, producing physiologically relevant concentrations of circulating adrenaline, has not been studied previously (Ball, Berkin & Inglis, 1984). Circulating adrenaline, at concentrations within the physiological range, has a bronchodilator effect predominantly in small airways in normal subjects. The lack of responsiveness of airway calibre to noradrenaline suggests that a-adrenoceptors are not impoi 'ant in the regulation of bronchomotor tone in normal subjects. REFERENCES BALL, S. G., BERKIN, K. E. & INGLIS, G. C. (1984). Hypokalaemia from I2 receptor stimulation by epinephrine. New England Journal of Medicine 310, BALL, S. G., TREE, M., MORTON, J. J., INGLIS, G. C. & FRASER, R. (1981). Circulating dopamine: its effects on the plasma concentrations of catecholamines, renin, angiotensin, aldosterone and vasopressin in the conscious dog. Clinical Science 61, BARNES, P. J., BASBAUM, C. B. & NADEL, J. A. (1983). Autoradiographic localization of autonomic receptors in airway smooth muscle. American Review of Respiratory Diseases 127, BOUHUYS, A., HUNT, V. R., KIM, B. M. & ZAPLETAL, A. (1969). Maximum expiratory flow rates in induced bronchoconstriction. Journal of Clinical Investigation 48, BRADLEY, G. W., MILLS, R. J. & HENDERSON, A. K. (1976). Effects of beta-adrenergic blockade and stimulation on airways in normal subjects. Postgraduate Medical Journal 52, CABEZAS, G. A., GRAF, P. D. & NADEL, J. A. (1971). Sympathetic versus parasympathetic nervous regulation of airways in dogs. Journal of Applied Physiology 31,

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