AGE-RELATED DIFFERENCES IN THE SECRETION OF CALCITONIN IN FEMALE RATS

The mechanism that causes hypercalcitonemia in female rats and is asso ciated with aging was investigated. Young (3 mo), adult (8 mo), middle -aged (12 mo), and old (21 mo) rats were infused with CaCl2 and were b led from a jugular catheter after a CaCl2 challenge. To mimic some of the hormonal changes caused by aging, the anterior pituitary (AP)-graf ted ovariectomized rats with hyperprolactinemic syndrome were used to mimic the physiological status of aging. The rat thyroid gland was inc ubated with or without ovine prolactin (oPRL; 40 or 80 ng/ml) at 37 de grees C for 30 min. Old rats possessed the lowest levels of plasma est radiol and progesterone yet had the highest levels of plasma prolactin and calcitonin (CT) compared with young, adult, and middle-aged rats. The basal release of thyroid CT in vitro in thyroid glands gradually increased with age. Compared with cortex (CX)-grafted rats, the AP-gra fted rats possessed higher levels of plasma PRL, basal and CaCl2-induc ed levels of plasma CT, and the release of thyroid CT in thyroid gland s. After stimulation with oPRL, the in vitro release of thyroid CT inc reased in both CX- and AP-grafted rats. These results suggest that the hypersecretion of CT in old rats is due at least in part to hyperprol actinemia.