Ovarian hormone effects on activity, glucoregulation and thyroid hormones in the rat

Ovarian hormonal influences on the range of physiological and behavioral variables which combine to affect overall energy balance are poorly delineated. In the present study 4 groups of virgin, female rats (intact, ovariectomized, ovariectomized with estrogen replacement and ovariectomized with estrogen plus progesterone) were allowed access to running wheels and activity; food intake and weight gain were measured initially under food restricted, then under ad lib conditions. Serum insulin, glucose, thyroxine (T4) and triiodothyronine (T3) were determined on trunk blood samples obtained at the end of the experiment. Ovariectomy resulted in an increased rate of weight gain through reduced activity and T3 but food intake was unchanged. Insulin levels were greatly reduced. Estrogen replacement restored activity to the intact group's level and normalized weight gain. Insulin and T3 were also raised to control levels but T4 was reduced as was serum glucose. Estrogen plus progesterone replacement reduced weight gain markedly and increased T3 with normal T4. Despite the lower body weight this group was hyperglycemic and hyperinsulinemic suggesting insulin resistance. The results have important implications for the glucoregulatory and energy balance perturbations of ovarian hormone fluctuations and focus particularly on progesterone.