Effect of the imidazoline-derivative ST-91 on heart rate and blood pressure in healthy man.

1 ST-91, 2-(2,6-diethylphenylamino)-2-imidazoline hydrochloride produces in animal experiments bradycardia, and in larger doses, also hypertension, due to α-sympathomimetic activity and probable central sympathetic inhibition. 2 The effects of ST-91, after oral administration, were studied in 10 healthy volunteers. A dose-dependent, significant decrease of the heart rate was observed. On average the resting heart rate was reduced by 11-19 beats/min (15-29%). During exercise the decrease of the heart rate was less pronounced. After the largest dose there was a fall of the systolic blood pressure during exercise averaging at 14-15 mmHg (11-12%). Otherwise the blood pressure remained unchanged. 3 Eight out of the 10 test-subjects complained of hair-raising and goose-flesh after all doses, due to the α-sympathomimetic effect of the drug. No toxic effects were observed.