The Selectivity of Xamoterol, Prenalterol, and Salbutamol as Assessed by Their Effects in the Presence and Absence of ICI 118,551

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Abstract
The selectivity of single oral doses of xamoterol, 200 mg, prenalterol, 50 mg, and salbutamol, 8 mg, was compared in eight healthy male volunteers by measuring their effects on sleeping heart rate, supine heart rate, blood pressure, forearm blood flow, finger tremor, and exercise heart rate in the presence and absence of the specific .beta.2-adrenoceptor antagonist ICI 118,551, 25 mg. Xamoterol, 200 mg, increased sleeping heart rate and systolic blood pressure, decreased exercise heart rate, and had no effect on diastolic blood pressure, forearm blood flow, or finger tremor. The concurrent administration of ICI 118,551, 25 mg, did not alter these results. Supine heart rate was increased by xamoterol and did not differ from that for xamoterol with ICI 118,551. Prenalterol, 50 mg, increased sleeping heart rate, supine heart rate, systolic blood pressure, forearm blood flow, and finger tremor, decreased diastolic blood pressure, and had no effect on exercise tachycardia. The concurrent administration of ICI 118,551 with prenalterol reduced the increase in sleeping heart rate, supine heart rate, and forearm blood flow, and reduced the fall in diastolic blood pressure caused by prenalterol alone. The increase in finger tremor following prenalterol with ICI 118,551 tended to be less than that following prenalterol. Salbutamol, 8 mg, increased sleeping heart rate, supine heart rate, systolic blood pressure, forearm blood flow, finger tremor, and exercise heart rate, and caused a fall in diastolic blood pressure. When salbutamol, 8 mg, as administered with ICI 118,551, 25 mg, the only changes detected were a small initial increase in finger tremor and a small rise in diastolic blood pressure. These results indicate that, at the doses studied, xamoterol is a cardioselective .beta.-adrenoceptor partial agonist, that salbutamol is a selective .beta.2-adrenoceptor agonist, and that prenalterol has agonist activity at both the .beta.1- and .beta.2-adrenoceptors.