Clinica Chimica Acta 274 (1998) 53–61 Sex differences and age-related changes in human serum aminopeptidase A activity a a a ´ ´ ´ ´ Jose M. Martınez , Isabel Prieto , Marıa J. Ramırez , Marc de b a a a ´ Gasparo , Francisco Hermoso , Jose M. Arias , Francisco Alba , a, * ´ Manuel Ramırez a ´ ´ Unit of Physiology, University of Jaen, 23071 Jaen, Spain b Novartis Pharma, CH-4002 Basel, Switzerland Received 21 October 1997; received in revised form 17 February 1998; accepted 21 February 1998 Abstract Given that aminopeptidase A is primarily responsible for cleaving aspartic acid and converting angiotensin II to angiotensin III, the purpose of the present study was to evaluate the activity of aminopeptidase A by determination of glutamate aminopeptidase activity (GluAP) and aspartate aminopeptidase activity (AspAP) (reported respectively as aminopeptidase A and angiotensinase A activities) in human serum during development and ageing, in an apparently healthy population of 139 male and 148 female subjects. To measure GluAP and AspAP we used glutamyl- and aspartyl-2-naphthylamide as substrates. Significant age-related increases were observed in GluAP activity in males and females and in AspAP activity in females. In males, there were no age-related differences in AspAP activity. A significant correlation was observed between age and GluAP activity in the population analysed as a whole or according to sex. No correlation was demonstrated between age and AspAP activity either in the whole population or according to sex. These results may reflect the evolution of the functional status of susceptible circulating substrates during development and ageing.  1998 Elsevier Science B.V. All rights reserved. Keywords: Aminopeptidase A; Human serum; Development; Ageing; Sex differences * Corresponding author. Tel. 1 34 53 212302; fax. 1 4 53 212141; e-mail: msanchez@ujaen.es 0009-8981 / 98 / $19.00  1998 Elsevier Science B.V. All rights reserved. PII: S0009-8981(98)00049-7