The effects of organic nitrates on prostacyclin biosynthesis and platelet functions in humans

Abstract

The results of prior studies indicate that nitroglycerin stimulates prostacyclin release by cultured endothelium and by the coronary vasculature in vivo. However, the accuracy of these findings in coronary vasculature relies on plasma samples obtained from the circulation via cardiac catheters, a procedure we have shown to stimulate prostacyclin release, thereby confounding interpretation of drug action. We studied the effects of short-acting (nitroglycerin) and long-acting (isosorbide dinitrate) nitrates on a noninvasive index of prostacyclin synthesis, excretion of urinary 2,3-dinor-6-keto-PGF(1α). Nitroglycerin was infused into six subjects to either a maximum of 480 μg/min or until mean arterial pressure fell by 20 mm Hg. Urine was collected for negative ion chemical ionization gas chromatographic, mass spectrometric analysis before and during the nitroglycerin infusion and for two 2 hr periods after nitroglycerin. The peak nitroglycerin infusion rate was 387 ± 67 μg/min, which caused a fall in supine blood pressure (systolic/diastolic) of 11 ± 5/14 ± 4 mm Hg and a 12 ± 3 beats/min increase in heart rate. Excretion of 2,3-dinor-6-keto-PGF(1α) (pg/mg creatinine) was unchanged from control infusion values (106 ± 19.5) either during (123 ± 21) or after (134 ± 14.6; 139 ± 36) nitroglycerin infusion. Platelet aggregation to arachidonic acid (0.33 to 1.33 μM) and epinephrine (1 to 10 μM) ex vivo was inhibited in only one subject in whom excretion of 2,3-dinor-6-keto-PGF(1α) was unaltered. Serum thromboxane B2 was not changed by nitroglycerin infusion. Similarly, oral administration of isosorbide dinitrate (10 and 40 mg four times per day) failed to alter 2,3-dinor-6-keto-PGF(1α) excretion from placebo values in patients with angina pectoris. Noninvasive measurements, indicate that nitrates failed to stimulate prostacyclin release in vivo; platelet inhibition during infusion of nitroglycerin was unrelated to altered prostacyclin synthesis in human beings.