Beta-adrenoreceptors in denervated skeletal muscles of the cat.

1. A number of sympathomimetic amines have been compared with (-)-isoprenaline for their ability to produce contractions in chronically denervated soleus and tibialis anterior muscles and to increase heart rate in bilaterally vagotomized anaesthetized cats. 2. The mean dose-ratios ((-)-isoprenaline equals 1) for adrenaline, orciprenaline and salbutamol were 2.9, 29.7 and 11.5 respectively in the tibialis anterior muscle and 3.5, 24.1 and 14.3 in the soleus muscle. The dose-ratios for noradrenaline were 21.1 in the tibialis anterior and 57.6 in the soleus muscle. 3. The dose-ratios ((-)-isoprenaline equals 1) obtained for the positive chronotropic effects of the drugs in bilaterally vagotomized cats were 14.5, 14.6, 29.6 and 24.2 for adrenaline, noradrenaline, orciprenaline and salbutamol respectively. 4. The beta2-receptor antagonists butoxamine and H35/25 antagonized the vasodepressor and skeletal muscle responses to (-)-isoprenaline to a greater extent than the cardiac responses, whereas the beta1-receptor selective antagonists practolol and H93/26 antagonized cardiac to a greater extent than vascular and skeletal muscle responses. 5. The results obtained suggest that the contractions of denervated skeletal muscle to sympathomimetic drugs result from stimulation of beta2-adrenoreceptors.