Species difference in the beta1/beta2-adrenoceptor selectivity of SM220CL in the cat and guinea-pig

Some problems encountered in the evaluation of new bronchodilating beta-adrenoceptor agonists

A series of phenylethanolamine derivatives were examined with respect to their bronchospasmolytic effect and their ability to depress the contractions of the soleus muscle in cat and guinea-pig. One group of compounds including D2343 (1-(4-hydroxyphenyl)-2-[1,1-dimethyl-3-(2-methoxyphenyl) propylamino]-ethanol HCl), a new beta 2-adrenoceptor agonist, appeared to be more effective in combating bronchospasm induced by histamine than in depressing the contractions of the soleus muscle in anaesthetized cat. This difference disappeared when serotonin was used to induce bronchospasm. Terbutaline antagonized histamine and serotonin equally well. Experiments in vivo and in vitro with guinea-pigs gave ambiguous results. Slowly developing effects was a common feature of the compounds showing the apparent effect separation. None of the available beta-adrenoceptor agonists appears to distinguish between the adrenoceptors in the airway smooth muscle mediating bronchial relaxation and those in the skeletal muscle associated with tremor.

The control of mucin secretion into the lumen of the cat trachea by alpha- and beta-adrenoceptors, and their relative involvement during sympathetic nerve stimulation

We have tested the effects of phenylephrine, dobutamine and salbutamol, alpha-, beta 1- and beta 2-adrenoceptor agonists respectively, on the output of radiolabelled mucins into the cat trachea in situ. Phenylephrine significantly increased mucin output, an effect inhibited by the alpha-adrenoceptor antagonists, thymoxamine or prazosin, but not by propranolol. Dobutamine increased the output of 35S-labelled mucins greatly and had a smaller effect on 3H-labelled mucins. Propranolol blocked these effects but thymoxamine did not. At high doses atenolol, a beta 1-adrenoceptor antagonist, inhibited dobutamine's effect on 35S-labelled mucins. Salbutamol caused a small increase in mucin output and propranolol blocked this increase. Electrical stimulation of the sympathetic nerve supply to the trachea increased mucin output. Propranolol inhibited this effect; thymoxamine did not. We conclude that both alpha- and beta-adrenoceptors increase mucus secretion into the cat trachea but that only the beta-adrenoceptors respond to sympathetic nerve stimulation.

Comparison of the beta-adrenoceptor effects of soterenol and its 3-hydroxy, 4-sulphonamido isomer (MJ6987-1) in isolated tissues from the guninea-pig

1. Soterenol and its 3-hydroxy, 4-methanesulphonamido isomer (MJ6987-1) were compared with isoprenaline for beta-adrenoceptor mediated effects in guinea-pig atrial, tracheal, uterine and ileal preparations. In addition, MJ6987-1 was tested for its effects in the atria of cats, rabbits and rats. 2. Soterenol had a lower intrinsic activity and was approximately two to six times less active than isoprenaline in all preparations. 3. MJ6987-1 was a full agonist, being some 30--200 times less active than isoprenaline at beta 1-receptor sites and greater than 3000 times less active in preparations where beta 2-receptor activation was involved. 4. Change in the position of the ring substituents in soterenol leads to the production of beta 1-receptor selective agonist.

Effects of beta-adrenoceptor agonists on airway smooth muscle and on slow-contracting skeletal muscle: in vitro and in vivo results compared

Ten beta-adrenoceptor agonists were examined with respect to a) relaxation of pilocarpine-contracted trachea and depression of contractions of the soleus muscle of the guinea-pig in vitro and b) counteraction of histamine-induced bronchospasm and depression of contractions of the soleus muscle of the cat in vivo. There was a close correlation between the results obtained in vitro and results obtained on the corresponding tissues in vivo in spite of the different species used. A close correlation was also observed between effects on airway smooth muscle and on the soleus muscle contractions in vitro as well as in vivo for all compounds examined.

Agonistic and antagonistic actions of 3,4-dihydroxy-substituted phenoxypropanolamines in guinea-pig atria and trachea

1. Racemic mixtures of noradrenaline, adrenaline, isoprenaline, N-t-butylnor-adrenaline and their corresponding derivatives containing an oxymethylene (OM) link between the phenyl ring and ethanolamine side-chain have been tested for their effects on beta-adrenoceptors in isolated guinea-pig atrial and tracheal preparations. 2. In atrial and in spontaneously contracted tracheal preparations both the parent catecholamines and their corresponding OM-derivatives had a similar order of potency as beta-receptor agonists. 3. In carbachol-stimulated tracheal preparations the OM-derivatives were shown to have partial agonistic actions. 4. As in other phenylethanolamines and phenoxypropanolamines, both the agonistic and antagonistic potency of the OM-derivatives increased with increasing amine substitution.