Interaction of age and thyroid hormone status on beta-endorphin content in rat corpus striatum and hypothalamus.

These studies investigated the effect of aging on thyroid hormone regulation of beta-endorphin in rat corpus striatum and hypothalamus. In both brain areas, basal levels of beta-endorphin declined with age. In addition, age modified the response of beta-endorphin to thyroid hormone status. Hypothyroid rats aged 6 months (mature) exhibited a 67% mean decline in the level of beta-endorphin in the corpus striatum. Hypothyroid rats aged 20-24 months (senescent) exhibited no change in the level of beta-endorphin in the corpus striatum. Hypothyroid rats aged 6 months had a 28% mean decline in the level of hypothalamic beta-endorphin. There was no change in hypothalamic beta-endorphin content in hypothyroid senescent rats. Hyperthyroidism resulted in elevations of beta-endorphin in both the corpus striatum and hypothalamus in senescent, but not mature rats. Changes in beta-endorphin seen with age are at least in part thyroid hormone dependent. In addition, age is capable of modifying the response of brain tissue to thyroid hormone.