Effect of glyceryl trinitrate on distensibility of peripheral muscular arteries in humans is not mediated by prostaglandins

Abstract

Vasodilator prostaglandins have been claimed to be responsible for the coronary haemodynamic and venodilator effects of glyceryl trinitrate, although conflicting results have been reported. The aim of this study was to evaluate whether vasodilator prostaglandins play a role in the effect of glyceryl trinitrate on the distensibility of peripheral muscular arteries in healthy humans. A non-invasive technique, impedance plethysmography, was applied to the assessment of the effects of sublingual glyceryl trinitrate on the compliance of the forearm and digital arteries. The subjects studied received placebo (on two separate occasions), indomethacin (100 mg orally), or ibuprofen (800 mg orally) 1 h before glyceryl trinitrate (0.3 mg sublingual) on four occasions separated from each other by at least 48 h. Blood pressure and heart rate were measured by standard techniques; changes in peripheral arterial compliance were evaluated by impedance plethysmography of the forearm and finger. The study was double blind, cross over, placebo controlled, and randomised. 12 healthy male volunteers were enrolled in the study. All subjects were fasting for at least 10 h and had abstained from smoking and from methylxanthine or alcohol containing beverages. Glyceryl trinitrate increased heart rate by 11.6(SEM 1.6) beats.min-1 (p less than 0.0005) and diastolic blood pressure by 8.7(1) mm Hg (p less than 0.01), and decreased systolic blood pressure by 8.7(1.5) mm Hg (p less than 0.01) in placebo treated volunteers; the amplitude of the plethysmograph c wave in the forearm and in the finger was also augmented, by 120(11)% and 78(13)% respectively, indicating an increase in arterial compliance. The results obtained in the two placebo sessions did not differ, indicating good reproducibility of the system. Pretreatment with either indomethacin or ibuprofen did not modify the effects of glyceryl trinitrate on heart rate, blood pressure, and arterial compliance in the forearm and the finger. Both indomethacin and ibuprofen suppressed prostaglandin synthesis, as shown by the striking inhibition of serum TxA2 concentration, by 97.2(1.5)% and 93.7(3.0)%, respectively. Sublingual glyceryl trinitrate, in doses used clinically, induces a reproducible increase in peripheral arterial compliance in healthy volunteers; prostaglandins do not play any significant role in this effect.