Dose-response relationship in normal subjects of prenalterol, a beta-adrenergic agonist with positive inotropic and resistance lowering effects

Age and sex differences in cardiovascular reactivity to adrenergic agonists, mental stress and isometric exercise in normal subjects

Dose-response curves for intravenous bolus injections of isoprenaline were carried out in 40 normal subjects, in four groups of 10 comprising young and middle-aged males and females. The isoprenaline dose required to raise the heart rate by 50 beats/min, the CD50 (chronotropic dose 50 beats/min), was calculated individually and taken as a measure of the beta-adrenergic responsiveness. Females had significantly higher sensitivity to isoprenaline than males, i.e. lower CD50 values (95% confidence interval 0.07-0.11 versus 0.12-0.17 micrograms/kg body weight, p less than 0.001), and young subjects had higher sensitivity than middle-aged subjects (95% confidence interval for CD50 0.07-0.10 versus 0.12-0.18 microgram/kg body weight, p less than 0.001). Dose-response curves were also carried out for intravenous prenalterol, a partial beta 1-adrenergic agonist. The maximal heart-rate response to prenalterol (delta HRP) showed a significant inverse linear relationship with the CD50 (delta HRP = 44.8-0.11 x CD50, r = -0.53, rs = -0.69, p less than 0.001). A mental stress programme and isometric exercise gave significant increases in heart rate and blood pressure for all groups, but there was no significant relationship between the CD50 and the heart-rate response. By applying a theoretical model, developed by Kenakin and Beek [13], to the isoprenaline-prenalterol data, it is suggested that the observed age and sex differences in beta-adrenergic responsiveness are caused by a tissue-related difference in the stimulus-response mechanism.

An assessment of the partial agonist activity of Ro 31-1118, flusoxolol and pindolol in man

1. The effects of single oral doses of three beta-adrenoceptor partial agonists (Ro 31-1118, flusoxolol and pindolol), two beta-adrenoceptor antagonists (propranolol and atenolol), two beta-adrenoceptor agonists (salbutamol and prenalterol) and placebo on sleeping heart rate, quality of sleep, supine heart rate, exercise heart rate, blood pressure, forearm blood flow and finger tremor were studied in eight healthy male volunteers. 2. Sleeping heart rate was increased by Ro 31-1118, flusoxolol, pindolol, salbutamol and prenalterol and decreased by propranolol and atenolol. 3. None of the drugs studied affected quality of sleep. 4. Supine heart rate was increased by flusoxolol, prenalterol and salbutamol, unaffected by Ro 31-1118 and pindolol and reduced by propranolol and atenolol. 5. Exercise heart rate was reduced by both beta-adrenoceptor antagonists and the three partial agonists and unaffected by salbutamol and prenalterol. 6. Systolic blood pressure was increased by Ro 31-1118, flusoxolol, salbutamol and prenalterol, unaffected by pindolol and reduced by propranolol and atenolol. Diastolic blood pressure was reduced by salbutamol and prenalterol. 7. Forearm blood flow was increased by Ro 31-1118, salbutamol and prenalterol, unchanged by pindolol and flusoxolol and decreased by atenolol and propranolol. 8. Finger tremor was increased by Ro 31-1118, flusoxolol, pindolol, salbutamol, and prenalterol. 9. beta-adrenoceptor partial agonists have different effects on the cardiovascular system and finger tremor to beta-adrenoceptor antagonists. 10. While Ro 31-1118 and flusoxolol are antagonists mainly at the beta 1-adrenoceptor they have agonist activity at both beta 1- and beta 2 adrenoceptors. 11. While pindolol is a non-selective antagonist its agonist activity is mainly at the beta 2-adrenoceptor.