Oestrogen production by the goat mammary gland: transient aromatase activity during late pregnancy

Mammary tissue from goats had significantly higher aromatase activity at 148-149 days of pregnancy than earlier in pregnancy or during lactation. Aromatase activity was determined by production of 3H2O from 1 beta-3H]androstenedione that was inhibited by 4-hydroxyandrostenedione. The time of maximum aromatization was during peak mammary output of oestradiol-17 beta described previously in vivo in the same species. Aromatase activity in the mouse mammary gland was low and no peak was observed in late pregnancy. It is concluded that the oestrogens produced by the mammary gland in the late-pregnant goat are formed by aromatization of androgens.