Comparative effects of glyceryl trinitrate and amyl nitrite on pulse wave reflection and augmentation index.
OBJECTIVE
The influence of vasodilators on augmentation index (AIx) offers a simple, rapid and noninvasive method of evaluating vascular function. Glyceryl trinitrate (GTN) is widely used as an endothelium-independent vasodilator, although other nitrates that are shorter acting may have advantages in clinical studies. The aim of this study was to compare the effects of two short-acting nitrates, GTN and amyl nitrite, which have differing pharmacodynamic profiles.


METHODS
Twenty-one healthy volunteers (15 male; mean age 35 years, range 21-56 years) attended on three occasions and received sublingual GTN (0.5 mg for 3 min), inhaled amyl nitrite (0.2 ml inhaled for 30 s), or no treatment in a randomized cross-over design. Haemodynamic responses of AIx, blood pressure and thoracic bioimpedance (heart rate, cardiac index) were assessed by measurement at baseline, every 60 s for the first 5 min, and then every 5 min for a further 55 min.


RESULTS
AIx was reduced by amyl nitrite (peak effect -9 +/- 2% at 1 min, P < 0.002) and GTN (peak effect -12 +/- 3% at 4 min, P < 0.05). Compared with amyl nitrite, the onset and offset of action of GTN was slower. Amyl nitrite initially increased heart rate by 27 +/- 4% (P < 0.001) and cardiac index by 13 +/- 3% (P < 0.001) whereas GTN had no significant effect (P > 0.05). Neither agent affected blood pressure.


CONCLUSIONS
GTN causes a slower and more sustained reduction in AIx than amyl nitrite. Although amyl nitrite causes a more rapid fall and recovery in AIx, it induces a reflex tachycardia that may limit interpretation of the initial (1 min) but not later (2 min) changes in AIx. The prolonged offset of GTN suggests that a sufficient washout period must be included when making repeated measures or when assessing the subsequent effects of other agents.
Greig
Lynn D
LD
Western General Hospital, Edinburgh, UK.
Leslie
Stephen J
SJ
Gibb
Fraser W
FW
Tan
Sherilyn
S
Newby
David E
DE
Webb
David J
DJ
D000328:Adult; D000680:Amyl Nitrite / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008365:Manometry / Q000379:methods; D008875:Middle Aged; D005996:Nitroglycerin / Q000494:pharmacology*; D011674:Pulse; D017534:Radial Artery; D014665:Vasodilator Agents / Q000494:pharmacology*
D014665:Vasodilator Agents; D000680:Amyl Nitrite; D005996:Nitroglycerin