Differentiation of receptor systems activated by sympathomimetic amines

A new preparation of the isolated intact trachea of the guinea-pig

A preparation is described in which the guinea-pig isolated intact trachea is subjected to repeated transmural electrical stimulation with alternating square wave pulses. The intraluminal pressure is continuously sensed by a pressure transducer. An increase in the intraluminal pressure is the predominant response to electrical stimulation. This response is prevented by low concentrations of atropine. After the initial rise a small fall in intraluminal pressure occurs; this is prevented by low concentrations of propranolol. The sensitivity of the preparation to various drugs is described.

Actions of some sympathomimetic bronchodilator and beta-adrenoceptor blocking drugs on contractions of the cat soleus muscle

1. (-)-Isoprenaline, salbutamol, orciprenaline and quinterenol injected intravenously decreased the tension and degree of fusion of incomplete tetanic contractions of the soleus muscle of the anaesthetized cat.2. Under the most sensitive conditions, the smallest effective dose of (-)-isoprenaline was of the order of 0.01 mug/kg intravenously. Salbutamol was usually 6-10 times, orciprenaline 20-30 times and quinterenol about 35 times less potent than isoprenaline. The effects of salbutamol were about 1.6 times, of orciprenaline about 1.8 times and of quinterenol more than 20 times as long lasting as those of (-)-isoprenaline.3. The effects of the sympathomimetic amines were blocked by propranolol, H56/28, H35/25 and butoxamine but not by ICI 50172. The combined results with agonists and antagonists indicate that the receptors involved can be classified as of the beta(2) type.4. The effect of the amines on the cat soleus muscle appears to be analogous to that causing enhancement of physiological tremor in man, which suggests that skeletal muscle tremor may be an occasional unwanted side effect of the use of these bronchodilators.

Study on some selective beta-adrenoreceptor blocking effects of 1-(4-nitrophenyl)-1-hydroxy-2-methyl isoproylaminoethane (alpha-methyl INPEA)

1. The effect of methyl substitution in the alpha-carbon position of the ethanolamine side chain of INPEA was investigated on its beta-adrenoreceptor blocking activity in the isolated turtle heart and anaesthetized cats.2. In the turtle heart preparation, the pA(2) value for erythro-alpha-methyl INPEA was 5.3, as compared with 6.9 for INPEA, while threo-alpha-methyl INPEA was extremely weak and its pA(2) value could not be determined.3. In the intact cat experiments, alpha-methyl INPEA produced a competitive blockade of the peripheral vasodilator effect of isoprenaline in doses ranging from 5 to 20 mg/kg. However, this agent had a minimal effect on the cardiac stimulant effect of the catecholamine.4. These results are consistent with the hypothesis that the beta-adrenoreceptors comprise a family of nonhomogeneous receptors and a selective blockade of only some, but not all, responses mediated through their activation can be achieved by specific molecular modification of the beta-adrenoreceptor blocking agents.

Salbutamol: a new, selective beta-adrenoceptive receptor stimulant

1. Salbutamol is a beta-adrenoceptive receptor stimulant. Its pharmacological actions are reduced or abolished by beta-receptor antagonists.2. In anaesthetized animals, salbutamol, given intravenously, was slightly less active than isoprenaline in preventing spasm of bronchial smooth muscle but was considerably less active as a cardiac stimulant and vasodepressor substance. Its duration of action was about 2 to 3 times that of isoprenaline.3. Salbutamol given by mouth or aerosol to conscious guinea-pigs, greatly diminished bronchospasm caused by inhalation of acetylcholine. By mouth, salbutamol was more active and had a longer duration than isoprenaline or orciprenaline without affecting heart rate. By aerosol, salbutamol was approximately 10 times as active as isoprenaline and 100 times as active as orciprenaline. Its duration of action was much longer than that of isoprenaline or orciprenaline. Only isoprenaline produced an increase in heart rate by the aerosol route.4. On isolated guinea-pig trachea salbutamol had about 1/10 the activity of isoprenaline, on isolated atria about 1/2000.

Some Aspects of the Biological Role of Adenosine 3',5'-monophosphate (Cyclic AMP)

Cyclic AMP (adenosine 3',5'-monophosphate or cyclic adenylate) has now been established as a second messenger mediating many of the effects of a variety of hormones. Several of the metabolic effects mediated by cyclic AMP are discussed, and it is suggested that certain other ("functional" or "mechanical") hormonal effects may be similarly mediated. In particular, the evidence presented supports the hypothesis that the positive inotropic response to the catecholamines is mediated by cyclic AMP. Although knowledge of the biological role of cyclic AMP has not been widely applied clinically, sufficient knowledge has now accumulated to make research in this area desirable.