Thus, negative findings in this study should not decourage other investigators to search elsewhere for possible positive relationships. Concerning the subjects' choice, it might appear difficult to find individuals around the age of 60 years free from atherosclerosis. One of the future challenges will be to more precisely define clinical or other relevant phenotypes so as to generate appropriate tools for this important research field. We thank Dr Herrmann for his comments. Differences in reactivity do exist between resistance arteries isolated from different vascular beds.
Differences also exist between arteries of different size.
This may be of particular importance when contrasting the results of our study employing arteries from the human mesentery with results from other studies which have used larger epicardial coronary arteries. Therefore, we would not wish the results of our study to discourage further investigation in this area. Just as there are differences in arterial reactivity according to size and location, there may be age-related changes in resistance vessel reactivity. The use of arteries from children may maximise the chance of isolating a difference in arterial response according to genetic variation if such a difference were independent of structural change. It has been suggested that differences in local angiotensin II activity may arise as a consequence of this variation, which in turn could provoke structural change due to growth-promotion within the artery.