The role of maternal thyroid hormones on the development of the brushtail possum, Trichosurus vulpecula

Thyroxine (T-4) is a vital hormone for the development of mammals. To deter mine the role of maternal thyroid hormones on organ development, methimazol e, an inhibitor of T-4, was first administered via a minipump to 13 mothers with pouch young between days 10 and 80 post partum for 28 days. Three you ng survived and 10 of the young died at 104.0 +/- 10.8 days post partum (me an, SEM). Methimazole was then administered for 28 days to 6 lactating adul t possums with pouch young at day 20 post partum. The effects of this treat ment on the maternal plasma concentrations of T-4 were monitored and the de velopment of the lung, kidney and brain of the young were examined at day 9 0 post partum. There was no difference in the morphology of the lung, kidne y and brain of pouch young at day 90 post partum whose mothers were treated with methimazole or saline. Thus methimazole administered to lactating pos sums for a short period early in lactation can cause the demise of the youn g about day 100 post partum although the cause of death is unknown. It is p ossible that the development of the central nervous system or some other vi tal organ has been inhibited, this altered state not being apparent morphol ogically. Nevertheless the marsupial appears to be similar to the eutherian in its requirement for thyroxine for normal development. However whereas t his requirement is apparent during fetal development and around the time of birth in eutherians thyroxine is of importance during pouch development in marsupials.