Effects of age and sex on the hepatic monoxygenase system: a correlative approach.

The following studies compare developmental patterns of a hepatic monoxygenase system using (1) the aminopyrine (Ap) breath test, (2) in vivo Ap pharmacokinetics (clearances) and (3) in vitro Ap demethylation by hepatic microsomes. Together, the three methodological approaches indicate that hepatic metabolism of Ap increases from the fetal stage through 70 days of age with the male showing a significantly greater drug metabolizing capacity than the female. However, sex and developmental patterns derived by the three methodologies do not necessarily correlate quantitatively, due to a number of complex variables (i.e., liver size, drug volume of distribution, etc.) less likely encountered in the adult of fixed age and mature sexual development.