Long-Term Hypothyroidism and Hypothalamus-Pituitary-Adrenal (HPA) Response in Adult Mice
Previous studies of the hypothalamus-pituitary-adrenal (HPA) axis in young rodents have found thiouracil-induced hypothyroidism to delay development of the axis past a relative stress non-responsive period. Little attention has been paid to the effects of long-term hypothyroidism on the function of this axis. The present study examined HPA axis response to an acute stress as determined by production of the glucocorticoid corticosterone, in mice made hypothyroid by thouracil exposure from conception to adulthood. The effect of injecting thyroxine (T4) or triiodothyronine (T3) on HPA response in these animals was also determined. Long-term hypothyroidism resulted in depressed body weight, subnormal levels of circulating T4, and elevated levels of T3. However, HPA axis response to an acute stress was normal in hypothyroid mice, and was not augmented by T4 injection for two weeks. On the other hand, two weeks of T3 injection allowed for a 70% increase in stress response as compared to either euthyroid or hypothyroid animals. The basis of the differential effect of the two thyroid hormones on stress response in hypothyroid mice remains to be determined.
Author Institution: Department of Biological Sciences, Bowling Green State University
The Ohio Journal of Science. v97, n1 (March, 1997), 10-13