Effect of nitroglycerin on blood rheology in healthy subjects.

Transdermal nitroglycerin (Nitroderm TTS 5) and a placebo were applied to 10 healthy male volunteers for 10 days. Before the first application and 6, 24, 48, 96, and 240 h thereafter, the viscosity of plasma and whole blood was measured and the packed-cell volume determined. During nitroglycerin application, the viscosity of plasma and whole blood was significantly diminished, and after 10 days it averaged 5% below the initial value. The greater the initial viscosity, the more marked was the drug-induced reduction: in 5 subjects with plasma and whole-blood viscosities near the lower limit of the normal range, there was only a temporary decrease and the values reverted to their initial levels after 4 days; in the other 5 subjects, whose whole-blood viscosities were near the upper limit of the normal range, a 10% reduction was still demonstrable after 10 days. In those subjects all values measured throughout the 10-day observation period were significantly below the initial values. The haematocrit readings followed the same pattern as the alterations in viscosity. It can be assumed, therefore, that the decrease in viscosity induced by nitroglycerin results from "internal haemodilution". The clinical relevance of the changes observed is discussed. The improvement in the rheological properties of the blood may contribute to the anti-anginal effect of Nitroderm TTS.