Observations on the effect of β-adrenoceptor blocking drugs on glyceryl trinitrate tachycardia.

1 The administration of 0.5 mg glyceryl trinitrate by chewing and keeping under the tongue increased heart rate in normal subjects in the supine and erect posture. 2 There was no significant difference between the responses in the same subject on repeated administration of glyceryl trinitrate on different days but there was a significant difference between the responses in different subjects. 3 The oral administration of practolol and propranolol reduced the responses to glyceryl trinitrate. The two drugs progressively reduced the increase in heart rate produced by glyceryl trinitrate; there was no significant difference between their effects. Propranolol produced a significantly greater reduction than practolol in the maximum heart rate that was produced by glyceryl trinitrate. 4 The administration of practolol (300 mg) twice daily by mouth to patients after an acute episode of ischaemic heart disease significantly reduced the increases in heart rate produced by standing and by glyceryl trinitrate in comparison to the responses in similar patients receiving a placebo.