Monoamine oxidase activities in human cystic and colonic arteries--influence of age.

The deamination of 5-hydroxytryptamine, phenylethylamine and benzylamine by monoamine oxidases (MAO-A and B) and semicarbazide sensitive amine oxidase (SSAO) respectively has been studied in homogenates of human cystic and colonic arteries by radiochemical assays. In cystic artery the deamination is mainly carried out by SSAO with a lower participation of MAO-B. The kinetic parameters were: to MAO-B the Vmax = 15.11 +/- 0.51 nmol/mg protein.h and the Km = 78.51 +/- 5.16 microM (+/- SE) and to SSAO the Vmax = 211.70 +/- 8.75 nmol/mg protein.h and the Km = 211.51 +/- 23.27 microM (+/- SE). We could not measure MAO-A activity in our experimental conditions and also the levels of catecholamines are very low and the histological studies show a poor innervation in these tissues. In colonic artery the kinetic parameters were: to MAO-B the Vmax = 5.09 +/- 0.31 nmol/mg protein.h and the Km = 29.12 +/- 4.55 microM (+/- SE) and to SSAO the Vmax = 273.67 +/- 8.35 nmol/mg protein.h and the Km = 197.89 +/- 21.81 microM (+/- SE). In this artery we could find MAO-A in five among the nine samples studied and the kinetic parameters were: the Vmax = 14.48 +/- 0.82 nmol/mg protein.h and the Km = 136.40 +/- 25.46 microM. As we have performed the experiments with human vessels from donors with different age we could not find any relationship between the activity or affinity, in MAO-B and SSAO, with age. Nevertheless, the results show in cystic artery an increase in the affinity of MAO-B with age when we consider the female group which suggests a possible role of the hormonal condition in this behaviour.