Development of sucrase activity: effect of maternal hormonal status and fetal programming of jejuno-ileal differences

The first part of the paper deals with the effect of changes in the mother's hormonal status on the development of the small intestine of her offspring. Administration of cortisone or triiodothyronine (T3) to pregnant rats evokes a precocious appearance of sucrase activity in the fetal small intestine. Administered to lactating rats, T3 evokes a precocious increase in sucrase activity in sucklings and leads to increased T3 levels and decreased TSH levels in the mother's milk and in sera of mothers and sucklings. These experiments show that (a) sucrase activity can be induced in the fetal period; (b) changes in the mother's hormonal balance during the fetal and suckling period can influence the development of the small intestine; and (c) levels of thyroid hormones in milk can be altered experimentally. The second part deals with jejuno-ileal gradients in villus size and sucrase activity. Both gradients appear in fetal jejunal and ileal implants developing in adult hosts. Our experiments indicate that (a) the gradients are already 'programmed' during the fetal period; and (b) direct contact with food, and proximity of the jejunum to the flow of digesta from the stomach, are not decisive for expression of the jejuno-ileal gradients, but may play a 'tuning' role.