This manuscript attempted to relate the levels of vasopressin and angiotensin in blood to ages by detecting several peptidase activity that are able to degrade these hormones. Unfortunately, the major problems of this works are:

1. The identity of the enzyme(s) is unknown. One doesn't know whether there is only one or several peptidases that is responsible for hydrolyzing the substrates used in the study. For example, The rate of hydrolysis of Arg-2NA or Ala-2NA by ApN is about the same based on a previous study. In other words, the result in Table 2 could be caused by one enzyme. The use of inhibitors are needed. For example, the use of bestatin rules out some cross reactivity by endopeptidases. Further, some aminopeptidases are sensitive to puromycin and some don't. These information would help the present work more convincing.

2. ApN is located on the cell membrane and some other aminopeptidases seem to be intracellular

(ref 1-4). However, the present work detected enzyme activity in serum implying these activity is secreted. Are these the same enzymes? Or should they be called ApN-, ApB-like activity instead? Unfortunately, neither the Introduction nor Discussion did not deal with this issue.

The result seemed to focus only the difference in activity without giving an idea of what is the general trend of the finding. Sometimes similarities are also worthy mentioning. Finally, the interpretation of the correlation values is wrong.