Changes in the bone and liver isoenzymes of alkaline phosphatase in postmenopausal women being treated with norethisterone.

The effects of norethisterone therapy on alkaline phosphatase isoenzyme activities were studied in a group of postmenopausal women. There was a significant fall in total alkaline phosphatase activity after 8 wk which was still in evidence after 24 wk. Both bone and liver alkaline phosphatase isoenzyme activities were decreased during the first 16 wk on treatment, but after 24 wk only the bone phosphatase activity was significantly lower than the pretreatment level. The other biochemical indices of bone metabolism and liver function were also measured during the study. The results indicate that bone specific alkaline phosphatase activity is a more sensitive index of bone activity than total alkaline phosphatase and that monitoring of total activity may in some instances be misleading.